he is mistaken in making a mystery of the screw-lathe, but with the die-stocks and chasing tools, who value a lathe for its shininess, or who limit threads or other data to which he refers in his would have doubled the number of their working themselves to the ivory pagoda business. But to published papers. screw tackle and the attendant apparatus; with the the intelligent amateur-who not only has feeling risk of confusion from the increased number, but for a finely-shaped vase or an eccentric column, without commensurable advantage as regards the but who may desire to make a piece of philosophipurposes to which they are are applied. cal apparatus comprising wheel-work and reguIt must, however, be freely admitted that advan-lating-screws-the first thing wanted is to know tage would ultimately accrue from making all new the number of threads per inch which he can cut screws of aliquot measures; and which, by gradu- with the beautiful Holtzapffel screw-tools which ally superseding the old irregular threads, would have been sent to him. Taking down Vol. II. of tend eventually, although slowly, to introduce a Holtzapffel's work, he finds himself confronted more defined and systematic arrangement in screw with the table which I have cited, and which seems tackle, and also improve their general character." to have been planned to prove that the ornamental At page 1,017, Vol. II., after giving a series of lathe is incommensurable with the doctrine of tables of all sorts of gauges for wire, sheet metal, ratio and the four rules of arithmetic. Now that &c. Holtzapffel goes on to remark:we have an Amateur Mechanical Society, this "From the perusal of the foregoing particulars question will no doubt be taken up, and, in a few of numerous gauges employed in different branches years, lathe-apparatus encumbered with screwof mechanical art, it will have been seeu that little threads which are only a barbarous survival of analogy on the one hand, but great confusion on rule-of-thumb-mechanics, will be as unsaleable as the other, exist in such of the gauges as have been the old microscope apparatus already is. referred to; and the author will now briefly state ornamental lathe-makers should carefully keep on the remedy he would suggest to obviate the hand the whole multitude of their obsolete screwdifficulty in the most simple and inexpensive man- tools is only due to those clients who have invested ner. in the present apparatus; but that they should continue to inflict upon a new generation of unwitting clients these incommensurable and mysterious screw-threads is a proceeding greatly to be deprecated, and one which, if persisted in, will assuredly turn awry the present currents of business.

The microscope makers of the last generation each screwed his own microscope with a gauge of his own for the purpose of making a slave of every one who invested in his apparatus, and of necessitating their always coming back to him for repairs and additions. The result was, that microscopists found themselves encumbered and worried with a heap of adapters, which had to be obtained whenever they needed to apply some speciality of another maker to their original stand. The nuisance of this became so serious, that the Royal Microscopical Society took up the question, and fixed upon a suitable gauge, which was known as the "Society screw.' This, to the great comfort of microscope users, and in no way to the detriment of microscope makers, has ever since been in vogue, and any objective can now be screwed on to any stand, while a microscope not having the universal screw is now unsaleable. The question is, why are ornamental lathe users to go on buying costly apparatus which necessitates their always going back to a particular maker for the most trifling repair, alteration, or addition, and simply because a mysterious "J screw or "N screw" has been used in its construction? And Mr. Evans, when asked by me to state the advantages which these screws possess over our public standard screws, frankly says: "There is no practical reason why a Whitworth thread should not be used, and one of the great features with regard to the latter is that you can get them any and everywhere." Now this is perfectly well-known to everyone who has studied the question: but it is a great thing to have the admission from Mr. Evans himself and the question which he will now be asked is, Why, then, victimise your clients by putting these mysterious screws nto the apparatus which they unwittingly buy on your recommendation as a scientific mechanic? ow have in my own laboratory a slide-rest in vhich the head of one of these screws has come off, and, instead of being able to walk into au ironLougers and for a few peuce buy a Whitworth bolt, I must either have my slide-rest packed up and sent away in order that this trumpery little belt may be replaced, or I must myself have forged and then screw up a steel bolt by one of the Holtzapffel tools. If for the latter job I have not time or not skill, the slide-rest runs the risk of injury in transit, my work is stopped for several days, and the cost is twice as many shillings as otherwise it would be pence. To an amateur in the country or in the Colonies the result is much

more serious.

I

"The remedy proposed to remove the arbitrary incongruous system of gauges now used is simply to employ the decimal divisions of the inch, and those under their true appellations."

That our

The gentleman who now, with such distinction, represents the Holtzapffel firm, has recently brought out the fourth volume of the series of As to what cross section the screw-thread should which his father produced the first three, and have, and how the cross section should be varied that volume has already reached a second edition. for various purposes-these are questions of infiThis volume fully maintains the scientific and nitely less importance than that which I now raise literary reputation earned by the first three. But-i.e., the question whether the pitch of our ornamany readers were disappointed at seeing in it no mental lathe-thread shall be commensurable or further scientific development of the screw-thread incommensurable with our English inch? I venquestion, and I confess to having been one of such ture to submit that in future no pitch other than readers. The only reference which I have noticed an aliquot part of the inch should be used unless in the fourth volume (page 163) reads as follows:- where necessary for the utilisation of existing "A wheel of 53 teeth has been introduced into apparatus. the table [of change-wheels], in order to enable the apparatus to cut a thread of the same pitch as the screws of the mandrils of Holtzapffel and Co.'s 5in. centre lathes; the approximate value of which is stated on page 673, Vol. II., as 9:45 to the inch. The table shows that 53 on the mandril and 50 on the screw [guide-screw ten turns to the inch] give a pitch of 9-433 (9.434) to the inch, as the result of the combination, which, although not theoretically correct, is a sufficient approximation for most purposes."

The fact, however, is clear, and it ought to be embalmed in the pages of the ENGLISH MECHANIC, for Macaulay's New Zealander to cite as an example of the "goings on " which impeded scientific progress in the days of Queen Victoria, and of the docility of the people who then bought ornamental lathes.

This passage from Holtzapffel's new volume is curious and interesting. In it a gentleman, one of our most eminent mechanicians, gifted also with admirable literary abilities, exhibits himself as inIt is perfectly true that the Holtzapffel screw-capable of perceiving that the thread on the nozzle tools can be purchased by anyone. But Holtzapffel's of a Holtzapffel lathe might be made an aliquot catalogue-which cau be got by post for eight part of the inch-say nine or ten threads to the stamps and is a most useful little volume-thus inch-as easily as an incommensurable number, describes (page 61, articles 2,011 and 2,012) the set such as 9:45! As an unintentional specimen of of screw tools. Twelve pairs for the deep threads, "how not to do it," this burdening each of his and twelve pairs for the shallow threads," i.e., clients with a useless extra brass change-wheel of 48 tools. Then in my laboratory I find a mahogany fifty-three teeth, instead of simply carrying out box of beautiful little taps, dies, &c (article 1847. that recommendation which his father so ably adp. 55), marked in sets "N," "P," R," "T."vocated, and screwing all new lathe-nozzles to an These consist of a screw die- stock, two tap- aliquot part of an inch, is very funny. wrenches, eight dies, twelve taps, and a gaugeplate with four screws, so as to size the bolts, and the screws-inside and out, when perfected; in all 29 pieces. Thus one has 77 surplus tools to buy, to store, to keep in order, aud to make no mistake about when using, simply because ornamentallathe makers have not yet adopted a standard aliquot thread. Of course one has to keep Whitworth tools also. As to the meaning of these mysterious denotements, "N," "P," "R," "T," experienced amateur will perhaps enlighten us, as Mr. Evans declines to do so, and there is no clue that I can find to them in Holtzapffel's volumes. Of course I can easily take wax or lead impressions of these taps, and measure out their details; but never yet having taken the trouble to do this, I have no means of knowing what they are, except that they are a beautiful This is really a delicious dispensation. By means little lot of tools, and that they work charmingly. of it an amateur desiring to use the guide Turning to Holtzapffel's classical volumes, I numbered 1, has to use with it the screw-tools find (Vol. II., pages 673-678), the following numbered 3; with guide numbered 2, the screwtable of the 48 screw-tools referred to in his tools numbered 4; with guide numbered 3, the catalogue, and which, as it may not be accessible screw-tools number 5; with guide numbered 4, to all the readers of the ENGLISH MECHANIC, I the screw-tools numbered 6; with guide numbered reproduce, together with Holtzapffel's comments 5, the screw-tools numbered 8; with guide thereon in the year 1846:

some more

"Approximate values of I.I. Holtzapffel's original screw threads:-No. 1, 6:53 threads in one inch; 2,8-25; 3, 9-45; 4, 1309; 5, 165, 6, 1989; 7, 22-12; 8, 2571; 9, 28 88; 10, 36 10; 11, 39 83; 12, 55 11. The angle of the deep threads is about 50°, of the shallow 60°."

"This irregularity of pitch would not have occurred had the screw-lathe, with its change wheels, been then in use; but such was not the case. Since the period at which H. and Co. made their screw lathe they have employed the aliquot threads for all screws above half an inch; indeed, most of these have also been cut in the screw-lathe. To have introduced the same method in the small binding screws which are not made in the screw

In Vol. IV., at page 108, a footnote will be found which explains an anomaly that puzzles most users of the Holtzapffel traversing or screw mandril. It reads thus:

The screw-guides ordinarily made for H. and Co.'s screw mandril lathes, are numbered 1 to 6: their threads correspond, in like order, to those numbered 3, 4, 5, 6, 8, 10, of the table, page 673, Vol. II.; these are generally found to suffice; but the number may be extended if required."

uumbered 6, the screw-tools numbered 10!
If the amateur is not up to this little
conundrum, he necessarily spoils his work when
he proceeds to screw it, as his work is run-
ning at one pitch and his screw-tool is cutting
another. As to the relation which Holtzapffel's
alphabet screw-tools bear to the mandril-guides,
or to the numbered screw-tools, I find no clue
anywhere in the four volumes. 1. Do they belong
to another series of screws altogether? 2. Are the
numbered screw-tools the same as some of the
alphabet screw-tools, and only varied in their de-
notation for the purpose of exercising amateurs in
the solution of conundrums? 3. If the answer to
query 2 be yes, which is which?

These considerations will not affect gentlemen

The great practical importance of this question is my apology for the length of this letter. James Edmunds, M.D.

Grafton st., Bond-st.

THE DANGERS OF OXYGEN MAKING.
(19692 -I AM glad this discussion has brought
out something worth reading, and I do hope the
lesson will not be forgotten by amateur lanternists.
A. W. Soward seems to have thought that I con-
demned his method. In this he is mistaken. I did
not for one moment wish anyone to believe that his
test-tube method was not correct; but what I did
say I repeat, it is not satisfactory." If every-
one who uses a lantern, or makes oxygen, was
a chemist, then I should give them a chemical test:
but I know too many of the readers of the "E.M."
who are not chemists at all, and would be alarmed
by the bubbling of the gas in the test-tube, and
the least bit of crackling in the tube would make
them discard the sample of manganese. Seeing is
believing, so the old people say, and when flame can
be seen on a shovel it is at once satisfactory and
complete. "F. I. C." only suggests a ladle, which
is not far off a shovel, but very few people possess
ladies, except perhaps soup-ladies, and I fancy the
use of the latter would bring on an explosion of
another kind. The simpler method is always the
better. I have in my laboratory a number of test-
tubes; so have many others, but not one out of
50 oxygen makers have a test-tube, while every-
body possesses a shovel. "F. I. C." has jumped
to a conclusion without giving the matter sufficient
thought. 1 did not say that I had had the
explosions, but that I had had samples of
manganese. The manganese, from which I
had the samples sent to me produced the explo-
sions. I should have been sorry to have been
any where near the retort when it burst, but I
happened to be in the town in which the first ex-
plosion occurred; it was at the residence of a
Colonel, and he had every precaution for safety.
He had a safety-cork in the top of a conical retort,
had indiarubber tube some 10ft. long, and he had
built into the recess the huge iron perforated cast-
ings I spoke of. I drove to the house, and cer-
taiuly I never saw a much greater wreck; the
casting had been blown loft. away, and removed
several bricks in the opposite wall by the force of
its impact. The ceiling gave way, and several of
the joists supporting the room above were moved
considerably, and had to be supported. Three of
the plate-glass windows in the room above were
smashed. This was something like what the
Americans would call a jolly big explosion, and,
even if not terrific, it certainly terrified every-
body in the place, and, as "F. I. C." says,
means exceeding great fear"; therefore, exceed-
ing great fear must mean terrific. Q. E. D.

"terror

I may say that, for over twenty years, we have received manganese from one manufacturer, and we have never once had a bad lot, and, using some four or five cwt. a year, oue would think by this that it did not need a test; nor does it, but I do personally test every barrel that is opened, and then I am sure as to its quality. I shall always test it; I would not trust to anybody's word as to

manganese. Trust yourself; don't deceive your- and hard wood-and two bolts, A and B; or,
self, and all will go smooth. Not long ago rather, the bolt A and steel pin B. The eye is
I heard of a queer case.
wedge-shape to and from the claw-foot; the foot
There were two casks in a cellar one filled with is turned to fit a metal ferrule somewhat smaller
manganese, the other with lampblack, the chemist's than the foot of the main leg. The end at A is
assistant had partly filled a paper-bag with the in. thick and 1in. wide, owing much to the
manganese when he was called to the bottom of the weight of the instrument. I have a 4in. refractor.
steps, and ladle in hand he went back to the wrong The bolt A is an ordinary bolt, driven into a hole
barrel and filled up the bag. Fortunately, the in the main eye, tight, to prevent its turning while
mistake was found out in time; otherwise the re- tightening or loosening the thumb-nut A; the
sults would have been disastrous. Everyone who steel pin is 5-16in. in diameter, driven into the
makes gas has his own little dodges or peculiarities. main-leg tight, to prevent its loosening; it projects
Some like making it on a fire. I do not recom-in. as shown in Figs. 3 and 4; by loosening the
mend the fire; better make it over a good gas- thumb-nut A, the extension-leg will drop off of
stove with a hood to nearly cover the bottom part the steel pin B, as seen in Fig. 3, which will permit
of the retort, allowing room for the heat to come of its being reversed, as seen in Fig. 4; by tighten-
round the retort. This will give plenty of heat and ing the thumb-nut, the eye is held in its place and
will allow the operator to make the gas quickly or out of the way, as it folds up inside the main-leg.
slowly as he may wish. For purifier, always use a With this device, I can raise or lower my tripod
glass bottle, and it is much better to use two in a minute, and at the same time avoid loosening
bottles, one with water in nearest to the retort, the the extension or extra leg; the bolt A should be
other empty nearest to bag. Through the glass can long enough to avoid taking the thumb-nut off.
be seen the least change in the rapidity of the Figs. 4 and 5 show the eye-face and side view,
evolution of the gas. I would not recommend the and also bend the claw-feet to prevent slipping,
use of a mercury bottle for making oxygen; the which I finds improves it much, especially when
bottles are so thick that they take a long time to the tripod is well spread out. I simply give the
heat and then become so hot that very often the above believing it to be useful to many, especially
upper part becomes choked and if they burst they those who exhibit in the street.
explode more like a shell than anything else. I
have heard of several explosions, dangerous ones,
with these mercury bottles. W. J. Lancaster.

EXTENSION TO TRIPOD-LEG OF
TELESCOPE.

D. C. Meeker. 32, Lorimer-street, Denver, Colorado, U.S.A.

SPOT AND PINHOLE-MODE OF

ADJUSTMENT.

[19694.]-THE thanks of your readers are due to [19693.]-I INCLOSE a sketch of an attachment Mr. Skelton for his letters on this subject; and as or extension to tripod-leg of telescope, which I| I have adopted his plan, I shall be glad to bear my

designed and have in use. The necessity of elevating the instrument at times, and lowering it at others, is obvious, no doubt, to all who read your

paper. Therefore, it will only be necessary to explain its construction, which consists of an extra piece of wood-which should be good straight grain

testimony to its extraordinary accuracy. I have
worked on somewhat different lines to the same
result, and my experience may perhaps be interest-
ing to amateur observers.

It will be evident that, where the accuracy is so
great, the appliances must be equally so, or they
will be a source of error in themselves. This,
however, I have found easy by adopting the follow-
ing methods:-

To find the exact centre of the mirror, divide the circumference of the cell of the mirror into three equal parts, taking care that the mirror is quite central in its cell. If it is not, allowance must be

made for this.

From these three points as centres, describe a small spherical triangle near the centre of the mirror, marking it with the compasses very slightly, just so as to show in the light, the sides of the triangle to be each 1-16in. beyond the spot to be formed. The radius in my case was 67-16in. Then either remove the silver by Mr. Skelton's plan, which I have done, or gum a circular piece of blackened paper of the size required - say, 3-16in.-exactly in the centre of the triangle (see Fig. 1) which is full size.

When adjusting the mirror in the usual way, this spot must be brought by the adjusting screws into the centre of the reflection of the flat (or shadow), and this can be done with astonishing accuracy and with the greatest ease. The shadow is so small, that it can be exactly estimated as being in the centre, and the slightest motion of the screws is observable. The three watch-springs also, which hold the flat in the centre of the tube, may be made themselves an additional test of accuracy; the three, being produced, will exactly meet in the centre of the spot. (See Fig. 2.)

Mr. Skelton, in his last letter (19611, p. 448),

places three other spots on his mirror, but they are unnecessary, nothing can be more perfect than the above.

The adjustment of the flat is made by Mr. Skelton's two pinholes, one at each end of the eye drawtube. The first, or outer one, is the usual adjustment-piece, or eyepiece with the lenses removed. The inner pinhole, after one or two partial failures, I perfected as follows:

I took a rod of brass fin. diameter (Fig. 3 full size), and put it into the chuck of a lathe, and turned down the small pin, b, perfectly true țin. in thickness, and the face, a, quite square. I then turned out a brass disc 5-32in. thickness, and rather larger than the size of the tube, and, drilling a hole in the centre, exactly fitted it on the pir (b). The disc was then slightly soldered to the

face (a), and then turned down to fit the tub leaving a very slight flange on the outside to pre vent its going into the tube, and to make it f quite square, taking care that the flange was d less diameter than the exterior of the tube, that t might not be pulled out when in the telescop The disc was now truly centred, and it was only to melt the solder and it was ready for the tube.

I have found it best to adjust the mirror, # named above, without the inner pinhole, as one can see better.

When this is done, bring the flat, in the usual way, concentric with the mirror, and make the eje tube as correct as this method will admit of, by trying it at different focuses, till it is concentricst all. Then "refine" the adjustment, as Mr. Skelton so well calls it, by introducing the iner pinhole, when the appearance, when perfect, ill be as Fig. 2, the shadow being seen in the centre of the pinhole with the spot in its centre, and s concentric ring of light all round. If it is not so at first, make it so with the flat motions, and the test of the perfection of the eyetube will be, that it remains so at all focuses, and also when the tube is rotated.

All this may seem a good deal of trouble; bat it must always be remembered that, no matter how perfect the mirror is, it will not do its best unless the adjustment is absolutely perfect, which only the last "refinement" can accomplish, so that it is worth it over and over again.

The satisfaction also of knowing that, on all o casions, you can see all that the night will allow, with splendid definition on good nights, and the light well gathered in" on all, must be experi. enced in order to be fully appreciated. Fordingbridge.

T. Westlake.

CHEAP MICROSCOPES. 119695.]-C. WELBORN, 19659, will find that an "equally effective instrument" cannot be produced at half the present prices, since it is not the cost of material, but skilled workmanship and time, that constitute the main part of the cost. The actual value of material is not more than five shillings in many microscopes, so that to substitute iron for brass could not make much difference. A perfectly efficient stand for ordinary purposes can be bought for a couple of pounds; beyond that, everything depends on the array of lenses and apparatus, and the best of these are costly; but very good ones can be got at a reasonable price.

To those who read the following letter, I say, Do not buy combinations of lenses-that is lin., in., and in. combined, if you can possibly do otherwise. No microscope so fitted gives satis faction for any period. A decent lin. will show more than such a built-up in. The letter of "J. F." is sound sense on the matter. Nearly every maker, as well as his Birmingham friends. supplies a very decent instrument for the prices he names, but the lenses have nearly always to be superseded by better ones. I should suggest purchasing a stand only, and then trying a decent lin say, Gundlach's, which is as good as any, and low in price; and afterwards he can get a good fis for 30s., and have a satisfactory instrument. E. Holmes.

Another class of engine, like the above, except mine, who was my superior officer in a merchantin the dome, which is over the firebox, and valve man trading to the East half a century ago, tried on boiler, with open weather-board, is represented his hand with an auxiliary, not in the shape of a by the "Anglia," "Colossus," &c.; there are 12 screw, but of paddles on each quarter, not revolvof this class. Both the latter class have over-hung ing, but in imitation of the savage "paddling his springs, and no brake on engine. own canoe." He had a small steam-boat running

There are three engines, Nos. 291, 292, and 293, | between Blackwall-pier and Greenwich, which having valve-chests on top of the cylinders; they was christened "Daddy Long Legs." His purse were built at Nine Elms. The dimensions are- was not strong enough to go on very long. That wheels 5ft., cycl. 17in. by 22in.; the bearings are was in 1843. inside.

me by one of the largest manufacturers of insulated wire. In a paper given by Dr. Siemens, and published in this journal, it stated the R. of F. M.'s should be ten times the R. of armature, and I cannot but think that if such be the case, Messrs. Siemens must construct their dynamos more on these proportions.

advice, but worked it out on the original lines (see

REPLIES TO QUERIES..

In their answers, Correspondents are repectfully requested to mention, in each instance, the title and number of the query asked.

[43383.] G. W. R. Engines (U.Q),
"Emperor" is of "Great Britain" class:-Cylin-
ders, 18in. by 24m.; driving-wheels (single) 8ft.;
heating surface, 1,952 sq. ft.
No. 2001 was
formerly a double-bogie tank-engine, belonging to
B. and E. R., with 9ft. drivers. She is now a
G. W. tender-engine, with leading bogie only:
cylinders, 17in. by 24in.; drivers, 8ft.; heating
surface, about 1,700 sq. ft.-C. R. M.

[43701.]-G. E. R. Engines Unless the numbers have been altered lately, 280, 291, and 305 must be Mr. Sinclair's 7ft. singles, with 16in. by 24in. cylinders. No. 242 used to be one of Gooch's 5ft. Gin. coupled-Cylinders, 15in. by 24in.; built by Sharp, Stewart, and Co., Manchester, and known as "Butterfly" class. No. 116 used to be one of Sharp's passenger engines: cylinders, 15in. by 20in.; single drivers, 5ft. 6in.

Now, as to "Anglo-Dane," who certainly has given us most willingly his experience and results; but, unfortunately, I cannot make out the length and sizes of the wire on his machine. I have followed up the correspondence between "Anglo Dane" and Mr. Kennedy, and have noted carefully the letter where "Anglo Dane" asks about the construction of dynamos, also the letter where he asks Mr. Kennedy's aid, he having constructed one which, unfortunately, would not work. How he succeeded in getting it to work he does not say, except that he did not follow Mr. Kennedy's page 310, present vol.), and on page 355, states that it will deposit 2-51b. of copper per square foot in 24 hours; but as to sizes and lengths, also weights of wire, we are in the dark. I should like Anglo Dane" to answer me these few questions: 1st, Theoretically, what weight of copper should the dynamo deposit per hour? 2nd, The lengths.-C. R. M. weights, sizes, and cost of wires, and method of [44083 and 44505.]—G.W.R. Engines.-Diwinding and joining up for R's? 3rd, The theore-mensions of G. W.R. engines, No. 1000 class tical, and also practical power for driving? 4th, (narrow gauge), have been several times given (see The theoretical and actual electromotive force, indices, back vols.). I sent sketch two years ago. also speed at which armature ruus? 5th, The total Cylinders are 18in. by 24in.; driving-wheels weight of machine? In fact, I should like to (single), 7ft.; heating-surface, 1,278 sq. ft.; know how the machine compares with the law laid weight, loaded, 32) tons.-C. R. M. down by Mr. Kennedy, as to the R. of F. M.'s being [41451.]-L. C. & D.R. Engines.-No. 29 has five times R. of armature. cylinders 16iu. by 22in.; coupled-wheels, 6ft. Gin.

-C. R. M.

20 per cent.; and at the temperature of fusing
platinum, about 15 per cent. It also varies with
the duration of carbonisation, and is greatest
when the process is slowly carried on. During
the normal carbon of the wood
carbonisation
is divided into two parts, one of which re
mains in the charcoal and the other escapes with
the volatile products. This division varies with the
temperature: thus, at 4829 the carbon remaining
in the charcoal is double that which escapes; be-
tween 572 and 662° the two portions are equal,
and at a higher temperature the quantity that
escapes is double that remains. The charcoal re-
tains a quantity of carbon proportionate to the
65 per cent. of carbon, at 572 73 per cent., at 754
temperature of carbonisation; at 482 it include
80 per cent., and at a higher temperature 96 per
cent.; but at no temperature is the product carbon
in a state of purity, as, however the charcoal may
be prepared, it always contains gaseous matter,
varying with the temperature of its preparation
when made at 482 it amounts to half the weight of
the charcoal, at 572 to one-third, at 662 to one-
fourth, at 752° to one-twentieth, and at the highest
temperature to about one-hundredth.
wood is carbonised in perfectly-closed vessels, the
resulting charcoal retains nearly the whole amount
of carbon; when thus charred at between 300 and
660 the percentage of carbon is about 80, which is
thrice that contained in charcoal prepared in the
usual way. The position of the pieces of wood in
the cylinders-namely, whether central or external,
in reference to their contents, affects its quality
The following table shows the produce of charcoal
from 1,000 parts of several varieties of dense sad
light woods, after exposure to a very high tempera-
tuce out of contact of air:
305 Box.

Fir

260 Lignum-vilæ
225 Oak....

Ebony
Brazil-wood
Botany Bay-wood 281
Eveoas-wood
King-wood
Tulip-wood
Satin-wood

When

201

The letter sent by "R. P.," page 426, has misled me, as it appears to have done "Earnest Eaquirer." In giving the data, &, of wires. I quite thought that it was for a machine that would give a light of 3,000 candles. Perhaps "R. P." would kindly say what light it would give in candles? On page 474" R. P.," speaking of the R. of armature, says, but as it is divided into two parts in the armature, its actual R. is only of the whole, or, rather large size (being taken from the official/ The stick of charcoal, when broken, should be

say. 1 ohm." I do not understand how it is only a-why not? "R. P." gives the R of an are lamp as 4 0 ohm, but in a book just published it gives one lamp when burning the R. from 1 to 14

ohua, two lamps in series R. from 4 to 5 ohm, three lamps in series R. from 8 to 10 ohm. Which is correct? It appears to me that the only way to tackle the difficulty is, first, to know the R. of lamp and conductors; secondly, to know the current required to give a certain light measured in candles, and then build a machine that will give the required current, in constructing which the cost of wire should be considered with the least amount of power required for driving.

Peraaps some readers will come forward and give us some data as regards what I have just stated as being required, and perhaps "Auglo-Dane," Mr. Hanson, and "R P." will give us data about building machine for same. As to what "Sigma says about here and there being found a reader who would build a machine successfully, I am inclined to think there are a good many who could, if they might have explained to them in a simple manner what is required in the way of data, &c., to work upon.

It, perhaps. can be found by looking up some half-dozen journals or so for the last two years; but it means a great deal of troubie, and as so many readers of the E. M." as there are, who show they have a thorough knowledge of electricity, surely they will come forward with the required information. As I look back the last three or four years "E. M.'s" I see how well the subjects of telephones, microphones, and gas-engines, &c., have been gone into; and with dynamos, I quite thought that we had a permanent friend in Mr. Kennedy, but who, I am sorry to say, has not given us any of his knowledge for some time. Hoping that by this, "Sigma" will have recovered his health, and that he may aid us with his information, I must bring this letter to a close, trusting that the replies will take up a good space in the "E. M." Quæstor.

the remarks of "Carstairs" (p. 70), whom I have
[41505.]-G. W. R. Eagines. In reference to
to thank for several interesting illustrations of
Caledonian engines, I may state that, in accordance
with my promise, I forwarded tracings of the 7it.
singles, G. W. R. and S. E R., more than two
years ago. Unfortunately, however, they were of
drawings), and, owing to that drawback, I sup-
pose, did not appear. I had no drawings available
at the time for reducing the drawings, and they
are no longer accessible to me.-C. R. M.
[44662]-Old G.W.R. Engines. -"Ixion,"
cylinders 15in. by 18in., driving-wheels 7ft.
(single); 'Courier," cylinders 18in, by 24in.,
driving-wheels (single) Sft. This latter engine
belongs to the Great Britain" and "Lord of the
Isles " class, and is still running. I have no par-
ticulars as to other engines mentioned.-C. R. M.
[45071.]-East Anglian Passenger Engines.
-In letter 16731 (Vol. XXX., p. 435) I gave a
tracing and some few particulars (which
supplement) of the engines asked about by "East
Auglia." They were 10 in number (Nos. 108 to
117 of the old Eastern Counties engines), and
were built by Messrs. Sharp and Co., Man-
chester. Cylinders, 15in. by 20in.; driving-wheels,
5ft. 6in.; leading and trailing-wheels, 3ft. 6in.;
inside cylinders and double frames: 147 tubes
(in.); heating-surface-tub s, 690-3ft.; firebox,
57'9tt.-total, 748 2ft; weight, 20 tons. Nos.
260 to 270 of the E. C. R., Nos. 1 to 50 G. N. R.,

Nos. 1. 10, 30,
70, and 80 classes on the L. B. and
S. C. R., 10. 80 and other classes on S. E. R.. and
many on L. and N. W. R., Midland. Great
Southern and Western of Ireland, and other
lines, were of same pattern. They were general
favourites, and did excellent work.-C. R. M.,
New Zealand.

mixed"

[45246.] Antares" Limelight Jet.-I am
sorry to have overlooked this till I saw it in the
Unanswered" column. The jet "Antares "sent
me to try with the gas-regulators was a very
ordinary
pattern, not at all one of the
best. A safety-jet cannot be altered to the mixed
form without more trouble or cost than it is worth;
and if "Novice" gets a good light with what he
has, and his oxygen-bag will last the time he wants,
he had better let well alone. We may have better
jets before next winter. I am certain the blow-
throughs can be vastly improved in light; and as
to mixed jets, there is not one that pleases ine to be
had at any reasonable price.-L. W.

220 Mahogany.
208 Beech

207

17

1

equally black throughout. Sugar, and certain other substances which neither contain nitrogen nor leave any residue after combustion, when iatensely heated in closed vessels, yield a pare charcoal.-F. BARKER COOKE.

[45308.]-Fusel-Oil (U.Q.)-No method has, I think, yet been devised for the estimation of fussioil present in small quantities in spirits. Its detection even is dutficult. Among the methods re commended are the following:-1. Rub some of the suspected spirit between the hands, and after permitting the ethylic alcohol to evaporate, which it will do more readily than the amylic alcohol, &c., forming the fusel-oil, endeavour to detect the presence of the oil by its odour. 2. Allow the spirit to stand over porous chloride of calcium for some hours and examine as to odour. This method is more delicate than No. 1. 3. To 150 parts of spirit add 1 part of potash dissolved in least possi ble quantity of water, well shake, slowly evapo rate to 15 parts, mix with 15 parts of dilute sulphuric acid, allow to stand in a closely. stoppered bottle, apply se.-ALFRED W.

SoWARD.

[45303.]-Fasel-Oil (U.Q)-The best mode of detecting the presence of fusel-oil in spirit is to allow the spirit to evaporate slowly, as by rubbing it on the hand, or riusing a glass out with it and leaving it to stand till the odour of the ethylic alcohol is no longer perceptible; the smell of the fusel-oil, being no longer disguised by the alcobel, becomes apparent. Diluting the alcohol with warm-water likewise brings out the smell of the fusel-oil. The complete removal of fusel-oil from spirit is a matter of considerable difficulty, and is seldom attained on the large scale. Simple distillation will not effect the object, although the boiling points of ethylic and amylic alcohols differ from one another very considerably; common alcohol boiling at 79° C, and amylic alcohol at 132. The method most generally adopted consists in absorbing the fusel-oil by wood-charcoal. To give the charcoal its full absorbing power it mast be recently ignited and left to cool in well-closed vessels; it is then reduced to coarse powder is rotating barrels containing a few iron balls. To effect the defuselation with the smallest possible quantity of charcoal, the spirit may be made to trickle through a number of casks filled with the charcoal, and placed one above the other. Accord ing to Ludersdorff, 2 quarts (or 2-28 litres) of spirit of 50 per cent. Tralles, require for defuselation the following quantities of different kinds of char coal:Potato-spirit. Corn-spirit

To Bleach Guttapercha.-Dissolve the gutta- [45263.] Charcoal Blacking (U.Q) In percha in twenty times its weight of boiling beu- making charcoal the billets are formed into a zole, add to the solution plaster of very good conical pile, which, being covered with earth or quality, and agitate the mixture from time to time. clay, is suffered to burn with a limited access of By reposing for two days the plaster is deposited, atmospheric air, by which its complete combustion, and carries down with it all the impurities of the or reduction to ashes, is prevented. Another and guttapercha insoluble in benzole. The clear liquid a more perfect mode is that of submitting wood to decanted is introduced by small portions at a time a red heat in a kind of distillatory apparatus, into twice its volume of alcohol of 90 per cent., consisting of cast-iron cylinders, from which issue agitating continually. During this operation the one or more tubes for the escape of gaseous matters guttapercha is precipitated in the state of a pasty and vapours. A third method consists in exposing mass, perfectly white. The desiccation of the it to the action of highly-heated steam. The guttapercha thus purified requires several weeks' quantity of charcoal obtained from wood decreases exposure to the air, but may be accelerated by in proportion as the temperature increases. trituration in a mortar, which liberates moisture 482 (Fahr.), the average product of charcoal is which it tends to retain. 50 per cent.; at 572°, 33 per cent.; at 752, about These numbers, must, however, be understood

[45570.]-Slide-Bars Cutting of Loco.-This query must be answered by another. Do slideIf "C.O." knows of a case, there is some not bars cut more when the engine runs tender first? altogether good work about.-NUN. DOR.

as merely approximate expressions of the relative [45552.]-Tait's Thermic Ventilator.- familiar hymn-tune without the music, at the same defuselising power of the several kinds of charcoal, To" CONSTANT READER IN ITALY."-My bedroom time playing the proper harmonies, is, unless you inasmuch as the detection of small quantities of is about 18ft. by 16ft. by 10ft., and is a very cold have a special gift for it, an exceedingly difficult fusel-oil in spirit is very difficult. In practice, room, having three walls exposed to cold winds thing to do. For instance, you know, say, the the treatment of spirit with charcoal is seldom from N. and E. I cannot say what temperature "tune," which is, of course, the treble part; to adopted, since a large quantity of spirit remains in a Bunsen burner would maintain in such a room, this, then, you have simultaneously to conceive the the charcoal, and a considerable portion of it having only tested a petroleum lamp, gas not ing bass with the intermediate harmonies. Memory, is lost by volatilisation during the transference of near my house. The lamp I use is the or Jary of course, cannot be dispensed with, and if you the saturated charcoal to the still; moreover, this table-lamp with two lin. wicks with a iron carefully play the tune from the music, reading operation takes a great deal of time. For this chimney 10in. long. This keeps the temperature in the names of the chords as you go on, and endea reason it is more usual to add the charcoal to the my room 12° to 14° higher than outside (4ft. from vouring to trace their relationship, you will, with spirit in the rectifying apparatus-which, however, ground), and although we have had pretty well of the aid of memory, gain experience in the right is a bad method, and never yields spirit free from fog this month, the room has been perfectly free from direction. Practice-so essential in every studyfusel-oil, at least in the first portion of the dis-it. I have slept in this room ten years, and during will enable you to do this more easily. But I am tillate; a better method is to pass the vapour of the winter have had a fire at night and frequently but half-satisfied with these suggestions. It seems the spirit through an apparatus filled with char- all day, but have never felt the room so agreeably to me that an intuitive grasp of the idea is necescoal, before it is condensed. A method very warm as it has been last winter and this, with the sary for acquiring any great proficiency in this generally practised is the addition of solution of petroleum lamp and thermic ventilator. I think branch of the art. I know several people who can, chloride of lime, before rectification, to the spirit the comfort consists in warm-air entering the room without any premeditation, extemporise with the previously defuselised with charcoal (1lb. of instead of cold, as when the ordinary fire is used.- greatest ease on auy melody that attracts their saturated solution of chloride of lime to 150 litres AN OLD SUBSCRIBER. attention, and yet be totally ignorant of the of spirit). One-third of this quantity of chloride of lime, is, however, sufficient, if, after it has grammar of the art. Others I have known, who been mixed with the spirit, an equivalent quantity had the faculty of writing and comprehending a score without the aid of the pianoforte, have been of chloride of zinc be added, hypochlorite of zinc playing. Perhaps "J. M. B." belongs more to the as helpless as a child in the matter of extempore being then formed, which is easily decomposed. Milk has long been used as a defuselising agent, latter. "Bannister" will perhaps indirectly help its action being probably due to the fat which it him to obtain his wish, and if his study of theory contains. "Breton" states that olive-oil, shaken has not been too superficial, he will be able to up with spirit containing fusei-oil, takes up the write on paper the melody of a hymn-tone he whole of that impurity, and when the whole is knows, afterwards harmonising it according to left at rest, settles down and may be separated by strict rules. I should advise "J. M. B." to try filtration. For operating on a large scale, he this as soon as he is able.-G. L. PEARCE. recommends that the spirit be filtered through a [15595.]-Quantity of Water Flowing in a layer of pulverised pumice stone, slightly drenched Biver at a Given Time.-" Aquarius" will find Turner" for his reply. Would he still further [45671.]-Wood-Turning.-Thanks to "Woodwith the oil. As soon as the oil in the a number of formula in Molesworth's pocketpumice becomes saturated with fusel-oil, the filtra-book; but it is obvious that the calculation of the oblige me by making rough sketch of spoke-shave? tion is interrupted, and steam at the pressure of quantity of water flowing through a channel is not two or three atmospheres is passed through the easily made, and that the result, without several pumice; the fusel-oil then volatilises, and the oiled elaborate experiments, could be only approximately pumice may be again used for defuselising.-F. correct. The formulæ are so formidable" that BARKER COOKE. I hesitate to quote them, and I must confess I have no time to work out an example. If "Aquarius" will refer to Molesworth, he will get at least an idea; and then if he consults "Neville's Hydraulic Tables, Coefficients, and Formula for Finding the Discharge of Water in Orifices, Notches, Weirs, Pipes, and Rivers," he will no doubt be able to calculate approximately the water power of any river or tidal basin.-Nun. Dor. [45597.]-Porcelain.-Pipe-makers' clay, china clay, or some potter's clay, to be obtained from the potteries, would suit this querist.-T. P.

[45338.)-Preservative for Iron Ships.-If Mr. Clifford will send me his address, I will give him the composition of an anti-fouling preparation for iron ships' bottoms, on which it is impossible for either animal or vegetable life to exist. The same composition will serve as an anti-corrosive also, and no previous or extra painting is required.-C. M. PIELSTICKER, 5, Sydney-terrace, Kilburn, N.W.

[45158.]-Pumps.-I did not recommend you to give the valves less lift. In fact, I think your valves are small enough to begin with. In my opinion, the area of the valves ought to be, as near as possible, the same area as the ram. A 30in. ram has an area of 708 56 square inches, and the size given of the valves (two loin. by Sin.) only gives an area of 210 square inches. I think you would find, on applying the indicator to the pump, that the diagram which it made would, most probably, slant more or less to the left, instead of being a rectangle, which it ought to be. This would show that the pump-barrel is not filled at each stroke, and the ram in descending would cause the knock to be heard and felt. If air were leaking into the pump, say through one of the suction-pipe joints, you would hear and feel the same knock or bump, but the indicator diagram would have the top pressure-line serrated or wavy. If I could only see the pumps, I could very likely point out the cause of the noise in a few minutes. Shall be pleased to give any further information.-LABOR OMNIA VINCIT.

tion.

[45571.]-Inclined Firebox of Loco.-Impossible to say without knowing the engine. Perhaps the firebox is extra long, and the idea is that the fuel shall shake down gradually to the front end. What is the amount of inclination ?NUN. DOR.

[45599.]-Wood Screw - Making. If you mean bench screws, they are made with a die fitted with cutters; tap and die, in fact, the same as screws of iron.-S. R.

-J. H. COYLE.

[45677.]-How to Dress Rabbit Skins.-I am not a practical furrier or currier; but if "Niobe" will follow my instructions, she will have rabbits, or other skins as soft and white as a kid glove. Take the skin as soon as it is off the rabbit, cut it open down to the tail, and down each leg, which makes it larger; peel off all the inside skin, which is easily done when it is fresh, lay it on a board perfectly level, pulling it a little longways, from the head to the tail, no nailing or stretching; now get a lb. alum, handful of salt, pint of water, put it in a stone jar, and boil it on the hob; when all melted and hot, but not boiling, take a stick and a piece of flannel, dip in the liquid, and well saturate the skin all over the flesh side; take particular care not to wet the fur. Then turn the edges up all round, and pour some of the liquid in the middle; see that it is perfectly level on the board, so that it does not run away. Let it remain thus for three or four days. Now comes the part that has generally failed with most people. Take the skin and hang it upon a nail, or fence, or anywhere to drain, and watch it narrowly, so as to get it just dry enough, but not enough, pull it crossways, and you will see it come too dry to pull out soft; try a corner, and if dry like white kid; experience only will make you perfect; you must then well pull, beat, bang it against a wall, and rub it as much as you can to soften it; then pumice-stone the flesh side, and well brush the fur side with a clothes brush; if properly done, it will be as soft and clean as any ladies' sealskin. If "Niobe" wants any further information, and will publish her address, I shall be pleased to tell her all I know. large rugs I have made, that now ornamentSWEEDLEPIPE COTTAGE.

I have four

[45614.]-Industrial Insurance Policies.This query could surely be answered by the secretary or solicitors of the society in question. As a rule, persons who insure in these societies can nominate anyone to receive the money.-E. G. M. [45654.]-Owen's Acme Incubator. -Your best plan would be to purchase one of Christy's Hydro Incubators, cheap form, price £2 108., or, if money is no object, you can get one similar to the gold medal one for £1 108., packing 7s. 6d. I preOn no sume you will have to pay carriage out. account use oil, as lamp flame tends to vitiate and dry the air, and an absolute necessity for successful incubation is to obtain a supply of pure air, especially after the tenth day. These incubators are heated by boiling water, in the following manner. [45544.]-Tait's Thermic Ventilator.-If A 90-egg machine will take the first time about 15 "Bronchitic" will look again carefully at the gallons of boiling water, heating-point 212, and the barrel, 10ft. 6in.; diam. inside, 4ft. in.; thick[45690]-Model Loco. Boiler.-Length of sketch, he will find that the fresh air passes up a effect of such a quantity will be a much higher temtube in the centre of the large tube; there is a perature in the egg drawer than is required, but which diam. outside, 1in.; distance of centres, 2in. ness of plates, 7-16in. Tubes-Length, 10ft. 11 in.; cap on the top of large tube, with a hole in the will rapidly fall as the sides and top of the incu-vertical, 2in. horizontal. No. of tubes, 250; area, centre, allowing the smaller tube to pass through and bator absorb the heat. After 12 hours, draw off 1,278.5 sq. ft. Outside firebox-Length outside, project about an inch. The discharge pipe is fitted to the whole of the water. Notice this, as if you do 6ft. 4in.; breadth, 4ft.; depth below boiler, 3ft. the large tube, and carries off all products of combus-not empty the machine the consequence will be that 33in.; thickness of plates, in., 2 stays. Inside fireThe elbow should be packed with wire.-AN it will require a larger supply the second time than box-copper. Length outside, 5ft. 9in.: breadth if it had been properly started. After the second outside, 3ft. 6 in.; top of box to grate, 5ft. 9 in.: [45548.]-Drilling Apparatus.-I beg to filling it will, at the expiration of 4 or 5 hours, regis- bottom of box to top of grate, 3in.; thickness of thank "T. P." for noticing my query. I find Iter in the egg-drawer heat from 120° to 130°. When tube plate, in. top, in. bottom. No. of stays, am quite correct, but perhaps I should have stated this heat is attained the machine may be said to 104. No. of firebars, 44, ĝin. apart; area of firethat it was under the head of "Index Plates for have been properly started; as soon as it falls to 108° grate, 17 sq. ft. Smoke-box (circular)-Length Gear-Cutting," which commences on p. 487, or 106, put the eggs in the drawer and draw off 2 outside, 2ft. 7in.; breadth outside, 5ft.; depth but the illustration in question is on p. 488. or 3 gallons of water, and replace by adding about below boiler, 4in. Chimney (taper) Diam. What I wish is some means of feeding the drill for 24 gallons of boiling water registering 2120. You lft. 4in. to 1ft. 6in.; height from top of rail, about 2in., while the pulley on drill-spindle cannot exactly fix the quantity required, but you 12ft. 10 in.; height of blast-pipe, 3ft. Cylinders, remains in the same plane as the driver.-TIE must keep the heat in drawer 100 to 104'; the tem18in. by 24in.; distance of centres, 2ft. 6 in.; MECHANICAL MASON. perature and conditions of atmosphere in the room, distance below boiler, 1ft. 4in.: centre of cylinder 145552 ]-Tait's Thermic Ventilator (U.Q.). hothouse, cellar used, and the circumstances of to centre of valve-spindle, lft. Oĝin.; diam. of summer and winter cause variations. -I cannot speak from experience of this ventilator, that you are communicated with by letter giving Length of steam, 1in.; length of exhaust, 34in. I will see piston-rod, 3in.; depth of piston, 4in. but I can assure "Constant Reader in Italy" that two Bunsen burners do very appreciably warm a you full information, as I am short of time just now. Slides-Travel, 4in.; lead, fore-gear, 7-32in.; small room. I have such a one (contents about back-gear, 9-32in.; steam overlap, lin. Eccen1,000 cubic feet) which is occasionally pressed into [45663.]-Music.-I understand that "J. M. B." trics-Throw, 31-16in.; diam., 1ft. 23in.; breadth, service for experimental work. I scarcely ever wishes to be able to reproduce a musical idea, 34in. Motion bars-Length inside, 3ft. Sin.; have a fire there, but, about an hour before using without relying upon his being able to play it breadth, 5in.; distance apart, 10in. Driving it, light a couple of Bunsens, or, more usually, a "mechanically"-i.e., remembering, as it were, wheels-Diam., 7ft., 24 spokes; distance of wheels single Bunsen and au ordinary gas-jet (Bray's, the movement of the hands: for playing a piece apart, 4ft. 54in.; cone of wheel, 1 in 15. Leading burning 5ft. per hour). At the expiration of the mechanically" from memory is a very different and trailing-wheels-Diam., 4ft.: 12 spokes; distime mentioned the room is, even in cold weather, thing to playing it with an intelligent understand-tance apart, 4ft. 5 in. Centre of leading-wheel to quite warm and comfortable.-ALFRED W. SOWARD.ing of the composition. To be able to reproduce a centre of driving-wheel, Sft. 6in. Centre of driv

OLD SUBSCRIBER.

-YANKEE.

Ports