in respect to the scrubbing of the clothes may be stated by saying, that the clothes will last 15 months where they only lasted 12; and that the cost of soap would be lessened to the amount of from 25 to 35 per cent." Mr. Chadwick then recommended to the members of the committee of the Society for Improving the Dwellings of the Working Classes, and the members of the committe of the Association for the Improvement of the Dwellings of the Labouring Classes, the immediate application of the invention to their model dwellings. Impressed with the great importance of the economy of fuel and the preven tion of smoke to the whole population, and knowing that in France as well as in England, there had been much attention paid to the improvement of domestic fire-places, and much unsuccessful invention, which had only failed in getting notice, he had suggested the necessity of trial works to determine experimentally the relative efficiency and economy of each method, authentically and impartially, for the public information. He had thought also that medals would be well applied for the same purpose. But the success of the old invention, now revived and simpli fied and cheapened, appeared to be so decisive as to leave nothing now to be desired but extensive and practical measures to ensure its adoption.

the country, though it might have its share of the cottage smoke, as compared with the time during which linen was useable in any part of London would be fully convinced that the entire abolition of the smoke nuisance from the domestic grate and range, as well as from the manufacturers, furnaces, would effect a reduction of more than one-half the expense of washing, as well as of the wear and tear of linen. He had some time ago occasion to enquire what those expenses were; he found that to the middle classes they made one twelfth or one-thirteenth of their income, often about half the rated rental of their houses; but taking all classes, high and low, those expenses could not be averaged at less than one shilling per head, per week, on the population, or to the two millions and a half of the metropolis, the washing bill was not less than £5,000,000 for the year's washing. On some points of the estimated saving there might be deductions, but on others there would be additions to be made, and, extravagant as it might appear to those who had paid no attention to the subject, the pecuniary economy in washing as well as in fuel, obtainable by the total abolition of the smoke nuisance, was understated at three millions per annum to the metropolis alone. If Lord Palmerston was duly supported in the abolition of the nuisance to private households as well as in the abolition of the smoke nuisance, a saving Mr. ELLIS seconded the motion. He said it was well would be effected of double the contribution which the known to all, the immense numbers of people who now Chancellor of the Exchequer was obliged to require from lived in this country and the comforts they enjoyed, as the metropolis by malt tax and other taxes in support of contrasted with former periods. They must have a stock the war. Smoke nuisance from the furnaces was, in the of what was called wealth, to enable those numbers to aggregate, the lesser evil, and the sources of the lesser live. They might talk of victuals, and clothing, and economy, but the economy of heat and power, as well as luxuries, but they could not do without heat. The best of smoke from the manufactorics, was only at its com-known material for producing heat was coal: and in promencement. At the discussion on smoke furnaces, Mr. ducing that heat it was very desirable to have some mode Wilson, of Price's Candle Company, had stated the of avoiding the creating of smoke. Now Dr. Arnott's execonomy observed, from the trial of various furnaces. position appeared to him so convincing that he saw they only at 11 per cent. of fuel; but in returns obtained could have a very largely increased supply of heat out of by direction of Lord Palmerston, a considerable number the same quantity of material as was now used. He corof private owners, who had adopted smoke-consuming dially seconded the motion of a vote of thanks to Dr. apparatus of various kinds, an average economy of 17 per Arnott. cent. was stated, and, in some instances, an advance to 25 per cent. of economy was admitted, together with the repayment of the outlays within short periods. In those discussions it was a common objection that they should not do one thing until another thing, which appeared to be improbable, was also done. It was objected that no good, that nothing of any consequence, would be done by compelling manufacturers to adopt measures for smoke consumption until similar compulsory measures were adopted towards the domestic fires. It appeared to him that the prevention of the smoke nuisance by the disastrous strike at Preston would afford some test of what might be accomplished by Lord Palmerston's measure of compulsory economy upon manufacturers, and he had requested his friend, the Rev. Mr. Clay, the Chaplain of the prison at Preston, to make inquiries for him. The following was his answer:-"I have made nu merous inquiries among respectable families of the operative class, and among the washerwomen who assist at the houses of the middle and lower classes; the general result is, that the discontinuance of the smoke was at once recognised as a great benefit by every woman who has to hang out her clothing to dry. The blacks' not falling, there was no necessity for washing clothes over again; the linen keeping cleaner when worn did not undergo so much scrubbing and wearing in the process of washing; and the quantity of soap used decidedly diminished. I made some inquiry also among the soap-dealers as to any change in the rate of demand for the article. They are sensible of a decided falling off, but the demand for everything has diminished, and it would be difficult to separate the decreased demand for soap arising from the decreased necessity for using it, from the decreased demand arising from want of means to purchase it. On the whole I feel satisfied that, comparing the washing of the town under factory smoke with its washing when free from it, as it has been for nearly six months, the saving

The CHAIRMAN, in putting the motion from the chair, added his testimony to the great value of Dr. Arnott's invention, which, he said, was so complete that with it people could almost whitewash the interior of their chimneys; and chimney sweping, and the cruelties thereof, which were still practised in the provinces, would be done away with. He then put the motion, which was carried with acclamation.

Dr. ARNOTT said he was gratified to find that the remarks generally made by different gentlemen who had addressed the meeting were in approbation of his invention. He had nothing more to say but to return his warmest thanks for their kindness.

read on Wednesday next, the 17th instant, The Secretary announced that the Paper to be would be "On Visual Education, as applied to Geology; illustrated by Diagrams and Models of the Geological Restorations at the Crystal Palace," by Mr. B. Waterhouse Hawkins, F.G.S., F.L.S.

ON A METHOD FOR PRESERVING THE SENSITIVE-
NESS OF COLLODION PLATES FOR A CONSIDER-
ABLE TIME.

BY JOHN SPILLER AND WILLIAM CROOKES.

(From the Philosophical Magazine.)

The extreme sensitiveness of collodion as compared with paper and other photographic surfaces, renders this material invaluable in all cases were rapidity of action is desirable, but up to the present time its use has been greatly restricted by the necessity for preparing the plate and completing the whole of the manipulatory details within a comparatively short space of time, thus rendering this

beautiful process practically inapplicable in all cases where the conveniences of a phothographic laboratory are not at hand.

For some time past we have been investigating the causes which operate to prevent the excited plate retaining its efficiency for more than a few hours. It seemed highly probable that the permanent sensitiveness of the film was principally dependent on the retention of a moist surface; and if by any artificial means this end could be secured, the original sensitiveness of the film would be, for at least a reasonable time, preserved unimpaired.

out, allowed to drain upright on blotting-paper until all the surface moisture has been absorbed (about half an hour), and then put by until required. The nitrate of zinc, which is still retained on the plate, is sufficient to keep it moist for any length of time, and we see no theoretical or practical reason why its sensitiveness should not be retained as long; experiments on this point are in progress; at present, however, we have only subjected them to the trial of about a week; although at the end of that period they were hardly deteriorated in any appreciable degree. It is not necessary that the exposure in the camera should be immediately followed by the development, as this latter process can be deferred to any convenient opportunity provided it be within the week. Previous to development, the plate should be allowed to remain for a few seconds in the original 30-grain

gallic acid or a protosalt of iron, and afterwards fixed, &c. in the usual manner.

The only attempts up to the present time to effect this object are, we believe, that of M. Girod*, who proposes to enclose the sensitive collodion film between two plates of glass, with only so much of the exciting silver solution as might be retained by capillary attraction; and thus by re-silver-bath, then removed and developed with either pyrotarding the evaporation of the water, to keep the surface moist, and consequently sensitive, for a longer period; and secondly, that of M. Gaudint, who suggests the use of perfectly air-tight dark frames or boxes, in which a number| of the wet plates could be arranged in a horizontal position, and there kept until required. Besides these two methods, it is well known that the plate will remain excited for a considerable time if kept immersed in a solution of nitrate of silver; in fact, a glass bath in the camera has been often used in cases where the length of exposure was likely to be too prolonged to admit of the plate being placed in the ordinary slide.

these reasons it might prove a valuable adjunct on the eve of a naval or military engagement, for accurately recording the positions of the forces.

The advantages of this process can scarcely be overrated. Besides the facility it affords of working in the open air without any cumbrous apparatus, photography may now be applied in cases where it would have been hitherto impracticable, owing to the feebleness of the light, e. g. badly illuminated interiors, natural caverns, &c.; if necessary, the exposure could be protracted for a week, or possibly much longer, and the deficiency of daylight compensated for by the employment of the electric or other artificial light. It will also be found useful where the plate must Instead, however, of having recourse to a mechanical be kept ready excited, but the exact moment of exposure means for preventing the evaporation from the surface, may depend upon possible contingencies rather than on we have endeavoured to avail ourselves of a chemical process, the will of the operator, or in cases where it would be imby the employment in the bath of substances having a pow-practicable to prepare the plate just before exposure; for erful affinity for water: in the choice of these, however, we are necessarily limited to such as are neutral in constitution, and do not form insoluble compounds with silver. The nitrates and acetates, especially the former, seemed most convenient for our purpose on account of their general deliquescent nature, and for our first experiments we selected the nitrates of lime, magnesia, and zinc, as most promising of success. These agents were at first tried in the abovementioned order; but from a few preliminary trials we were inclined to give the preference to the zinc salt, and, having obtained such satisfactory results with its use, are induced to communicate them at once rather than withhold them until our investigation of the other compounds shall have been completed. At first we endeavoured to add the nitrate of zinc direct to the exciting bath, but the quantity required to prevent so large an amount of nitrate of silver from crystalising out on the plate rendered the solution too dense to work with.

The following process can be recommended as having proved perfectly successful in our hands; we do not doubt that with more general use it may be considerably modified and improved, but at present we have rather contented ourselves with establishing the broad principle with such details only as will suffice to ensure good results, and to leave to a future period the consideration of those minor points which only a long experience can develope.

The plate, coated with collodion (that which we employ contains iodide, bromide, and chloride of ammonium, in about equal proportions), is made sensitive by immersion in the ordinary solution of nitrate of silver (30 grains to the ounce), and after remaining there for the usual time is transferred to a second solution of the following composition:

A small proportion of nitrate of zinc added to the ordinary nitrate of silver bath in no way interferes with its action, and might obviate the inconvenience sometimes felt during hot weather in photographic rooms, of the film becoming partially dry before exposure. If added in a still smaller proportion to the silver solution used for exciting the ordinary Talbotype paper* (without the employment of gallic acid), it is very probable that its sensitiveness may be preserved during a much longer period than is generally possible. As far as our experiments have gone, they tend to confirm this supposition; but at present we can hardly speak more confidently on this point, as it is still under investigation.

There are, no doubt, many other substances which might equally well answer the purpose of nitrate of zinc; besides those already mentioned, the nitrates of cadmium, manganese, and perhaps also those of copper, nickel, and cobalt might be found serviceable. Glycerine at first seemed to promise very good results, but the principal difficulty was the necessary impurity of the commercial product, in consequence of its being obtained from the exhausted leys of the soap boilers.

POSTAL REFORMS.

The Chancellor of the Exchequer, in his speech on the Budget the other evening, made the following remarks on this subject:-

"In the first place, there is one subject that prima facie might be supposed open to the consideration of a Minister of Finance driven to his wit's end to invent a new source of revenue, and that is an alteration in the rates of postage, because an alteration in the rates of postage would have this advantage-that the whole increase would be a net increase, while, on the other hand, the expenditure

This addition of nitrate of zinc to the silver solution in the

Talbotype process was suggested, we have been informed, some time back by the French, but not with reference to its keeping properties-only as an accelerator.

tionised.

would probably even be diminished. But the Govern-intelligence of the parties engaged in its conduct and ment is not disposed to propose any such alteration. We management for their own private interests. Some few of think that that scheme has been admirably successful- the Provincial Agricultural Societies, no doubt, awarded that it has contributed in a greater degree than even the premiums for good flax, but merely as a portion of the most sanguine could have anticipated to the comforts of " farmers' crop," and not in the broad light of a national the people-that it has been a great civilizing and production and manufacture. The Royal Dublin Society, humanizing project-that its moral advantages are not also, offered for competition, at their triennial exhibitions, less striking than its economic principles-and that in a prizes for the best specimens of Irish linens of different fiscal point of view it has more than answered the qualities and classes. There appears, however, to have expectations that were formed regarding it; for been an evident want of some substitute for the great while in 1840 the net proceeds of the postage revenue central Linen Board during this period; some Society to was 417,000l., in 1846 they had risen to 845,0007.: and in watch over and protect, in a national spirit, the general 1853 to 1,104,000l. It may be recollected that in the interests of the flax-growing and manufacturing commuyear of the Great Exhibition the addition to the postage nity; to introduce, after proper trial, improved modes of of the country was so enormous that a reaction in the operation; and to collect statistics on which to base calcurevenue was naturally expected; but if you look over the lations and confirm facts. list of annual proceeds since, you can scarcely detect which It certainly does appear to be a great pity that so many was the year of the Exhibition, so rapid and sosteady has years were allowed to elapse before this void, so long felt been the growth of the receipts under this most desirable and admitted by all, was filled up; years during which and most advantageous system. The doubling of the numerous important changes took place in the manufac postage, unless it wer extended to the district posts, turing process, more especially in the preparation of the would not bring inmore than 600,000l. a-year; to extend fibre. During this period the old systeins of hand-scutchit to the district post it would not be more than 700,000l.;ing and hand-spinning at home, and the selling of the 8) that, even under the present circumstances, the Govern-linens in the markets by the weavers, were quite revolument are of opinion that it would not be wise to attempt any change with respect to postage, except such change as The number of scutching-mills in the country had would tend further to extend the comfort and accommoda- greatly increased, and the flax prepared therein comtion of the public. They have lately succeeded in making manded such a preference, that hand labour in this branch further arrangements that would render interference at was much less in vogue. For spinning the yarn very the present moment peculiarly unseasonable. A most perfect machinery, driven by the powerful steam engine, valuable public servant, a man of unimpeached honour, of was also introduced, and this so completely outrivalled great assiduity, and of excellent abilities, who was Seere-in economy and regularity the handspun productions, that tary for the Post-office at the time this change was effected, in all (except a few of the very fine) numbers the handhas continued Secretary till the present time, and now re-spun yarn was speedily driven out of the market. tires from his office to another post in the public service, The Messrs. Mu holland were. I believe, the first prowith the full confidence and approbation of all those whom prietors of flax-spinning machinery in Belfast. Their he has served. But, without disparagement to any one, establishment was erected about 1828, and was managed it must be obvious to the committee that there is a great so well and so successfully that the owners amassed large advantage in placing the postage system under the care fortunes. For some years these gentlemen enjoyed almost and superintendence of the gentleman who has the happi-a monopoly, but soon other parties entered into the thriving ness of thinking that he stands regarded before the world, and consequently attractive business, and many new mills and that his name will be handed down to posterity, as were built both in the town and country. The Messrs. Murthe author of that system. Mr. Rowland Hill, within land, of Castlewellan,† and Messrs. Dumbar and Co., of the last few weeks, has assumed the office of Secretary of Gilford, were among the most intelligent and most prosthe Post-office, and though the advantages of the system perous of the spinners not carrying on their trade in the have been extended with great rapidity heretofore, yet, town of Belfast. They both relied on the production of from his parental fondness for that system, and his great the best, quality of yarn suitable for the home trade, while abilities, we may be justified in anticipating for the the majority of the Belfast spinners devoted their attention future a still more rapid increase than the country has ever to the lighter and less expensive qualities used in making seen or supposed possible. goods for export to warmer countries.

It is stated that at present there are about 80 flax spinning mills in Ireland, and that these contain fully 500,000 spindles, producing, if worked ten hours a day, fully nine millions of bundles of yarn per annum, worth about £2,250,000 at a moderate valuation. One can hardly fancy how the large quantity of yarn in use was made before the system of spinning by machinery was known and carried out. What an immense number of fingers and spinning-wheels would be required to turn out of hand the amount of yarns I have just stated! Yet, without doubt, a very considerable amount of hand-spun must at one time have been produced, to judge by the value of linens exported, and the quantity of flax grown. I here beg to give the number of acres of flax sown for some

*It may be interesting to state that the number of scutching mills in Ireland in 1852 (as furnished by the Government Returns) amounted to 956, containing about 5000 stocks, and driven chiefly by water power..

+ The Messrs. Murland dispute priority with the Mulhollands Ireland. as to which party first erected spinning machinery for flax in firms without doubt started their mills within the same year Be this as it may, these two highly respectable (1828). The Messrs. Murland are considered the first spinners in Ireland for prime quality, and the Messrs. Mulholland are proprietors of the largest mills and most machinery.

SIR,— The enunciation and establishment of a principle is not always the most difficult part of a question. We live in a practical age, and we must not only prove a proposition, but show how it can be carried out. Unless our scheme comprehended this, after setting out on principle, and The Royal Society, which was originally founded upon taking high ground, we are often obliged to descend to the philosophy of Bacon, gave a great impulse to practical expediency, and show in what manner, by certain comscience. The early proceedings of the Society, however, promises, our principles may be established. It is useless do not prove that its members were altogether emanci- to tell us what ought to be done, unless we are prepared to pated from the trammels of the astrologer and the show how it may be done. Now, to apply this to the alchemist of a previous age. The Society was chiefly proposition before proved respecting education and composed of the great, for the time had not arrived when libraries, it is necessary that we should call in aid not the great and the noble could unite with the horny-one but many co-operative means to effect our purpose. handed sons of industry in the pursuit of investigations which would add to the pleasures of the one class, or diminish the labour of the other.