hama Channel. The English call it Chesterfield. There is a small errour in the latitude of this Key, as given in our Connoissance des Temps. In our voyage I ascertained it to be 22° 7', instead of 21° 55'. The want of tolerable charts of this dangerous part, and the necessity of comparing the ship's place on the chart with sure data, render this observation interesting for those who sail without a pilot on board, As to the longitude, it was agreeable to what I obtained. by the timekeepers. This key must not be confounded with another of the same name on the south of the Great Bank of Bahama, and almost in the same latitude.

The accuracy of both of the observations here given I have verified by comparison with two Spanish charts published in 1779 under the ministry of Mr. Langara, and derived from the Hydrographer's Office at the Havannah,

in Brazil.

I know not where the latitude and longitude of San Sal- San Salvador vador, one of the principal cities of Brazil, in the Bay of All Saints, are to be found. When we anchored in that bay, Mr. Fonsera, Captain in the Portuguese navy, and superintendant of that harbour, told me, that its latitude. was 13°. and its longitude 42° 25'. An English work, in the hands of all the navigators of that country, gives them 12°. 46 and 41° 5. So considerable a difference led me, to pay as much attention to the subject as our short stay would permit; and I had an opportunity of finding both by lunar observations and the timekeepers, that its true longitude is about 41° 5. The latitude of point St. Antony I ascer tained by several observations to be 12° 59′8'. The time of high water is twenty minutes after three, mean time. The Variation of variation of the needle there in 1806 was 10° 20′ E.

IX.

On the Spontaneous Ignition of Charcoal: by B. G. SAGE, Member of the Institute, Founder and Director of the first School of Mines*.

MR.

the needle.

Charcoal fired

de Caussigni appears to have been the first who observed, that charcoal was capable of being set on fire by in grinding. the pressure of millstones.

ignites spon taneously.

In fine powder Mr. Robin, coinmissary of the powder mills of Essonne," has given an account in the Annales de Chimie, No. 35, p. 93, of the spontaneous inflammation of charcoal from the black berry bearing alder, that took place the 23d of May, 1801, in the box of the bolter, into which it had been sifted. This charcoal, made two days before, had been ground in the mill without showing any signs of ignition. The coarse powder, that remained in the bolter, experienced no alteration. The light undulating flame, unextinguishable by water, that appeared on the surface of the sifted charcoal, was of the nature of inflammable gas, which is equally unextinguishable.

Moisture promotes this.

In heaps heats strongly,

and takes fire,

Fired in pounding.

Ingredients for gunpowder

ground sepa

rately.

Manufacture.

The moisture of the atmosphere, of which fresh made charcoal is very greedy, appears to me to have concurred in the developement of the inflammable gas, and the combustion of the charcoal.

It has been observed, that charcoal powdered and laid in large heaps heats strongly.

Alder charcoal has been seen to take fire in the warehouses, in which it has been stored.

About thirty years ago I saw the roof of one of the low wings of the Mint set on fire by the spontaneous combustion of a large quantity of charcoal, that had been laid in the garrets.

Mr. Malet, commissary of gunpowder at Pontailler, near Dijon, has seen charcoal take fire under the pestle. He also found, that when pieces of salt petre and brimstone were put into the charcoal mortar, the explosion took place between the fifth and sixth strokes of the pestle. The weight of the pestles is 80 pounds each, half of this belonging to the box of rounded bell metal, in which they terminate. The pestles are raised only one foot, and make 45 strokes in a minute.

In consequence of the precaution now taken, to pound the charcoal, brimstone, and saltpetre separately, no explosions take place; and time is gained in the fabrication, since the paste is made in eight hours, that formerly required four and twenty.

Every wooden mortar contains twenty pounds of the mixture, to which two pounds of water are added gradually,

The

The paste is first corned: it is then glazed, that is the corns are rounded, by subjecting them to the rotatory motion of a barrel, through which an axis passes: and lastly it is dried in the sun, or in a kind of stove.

Experience has shown, that brimstone is not essential to Sulphur usethe preparation of gunpowder; but that which is made ful, not indispensable, without it falls to powder in the air, and will not bear car riage. There is reason to believe, that the brimstone forms a coat on the surface of the powder, and prevents the charcoal from attracting the moisture of the air.

charcoal im

portant.

The goodness of the powder depends on the excellence Goodness of of the charcoal; and there is but one mode of obtaining this in perfection, which is distillation in close vessels, as prac tised by the English.

The charcoal of our powder manufactories is at present prepared in pots, where the wood receives the immediate action of the air, which occasions the charcoal to undergo a particular alteration.

X.

Theory of the Detonation and Explosion of Gunpowder.

THESE

By the same

HESE two phenomena, which take place simultaneous- Cause of the ly, arise from different causes. The detonation is the noise, detonation of gunpowder, that is produced by the combustion of two parts of inflam

mable and one of oxigen gas.

The explosion, or discharge, is produced by the water of and its explethe nitre, and that which results from the decomposition of sion. the two gasses, which, being expanded by the fire, occupies fourteen thousand times the space it did before; and acts in the same manner as compressed air, to which its elasticity is restored, and the explosive effect of which is produced without detonation.

The inflammation of gunpowder by means of a spark Its ignition. arises from the ignition of the nitre and brimstone.

• Ibid. p. 425.

The

Inflammable

gas.

Foulness in gun barrels.

The inflammable gas is produced by the decomposition of the charcoal *; and the oxigen gas arises from part of the nitre, which is decomposed by the fire."

After the explosion of gunpowder, we find the inside of the gunbarrel coated with a mixture of alkaline sulphuret and charcoal not decomposed. This alkaline mixture attracts the moisture of the air, and forms a greasy coating within the barrel. If it be loaded in this state, part of the powder adheres to the sides of the barrel; and on discharging the piece, it catches, and produces what is termed hanging fire. The barrel of a fowling piece therefore should never be used a second day without cleaning.

Mr. Thomp- IN

son's analysis confirmed by Mr. Berthier

Component parts of

gypsum,

Charcoal of hard woods

best.

XI.

On the Sulphates of Lime, Barytes, and Lead.

N our last number, p. 174, we gave an analysis of two of these salts by Mr. James Thomson, who was led to the inquiry by the want of agreement between chemists respecting the proportions of the principles of the sulphate of barytes. A similar reason had led Mr. Berthier, mine engineer, to an investigation, which he has inserted in the Journal des Mines, for April, 1807, that has but lately reached this country. His analysis corroborates that of Mr. Thomson, after whose paper it would be superfluous to give Mr. Berthier's, I shall therefore simply quote the results

be obtained.

"From the experiments I have above described it follows:

"1. That pure common gypsum, in whatever state of mechanical division it may be, contains 21 or 22 per cent of pure water.

* In France charcoal of alder, poplar, willow, &c. is always used for making gunpowder. The intensity of the fire produced by such charcoal is less than of that from harder wood. The former, being more perous, would require more care in charring than the latter; and they cannot be said to be in the state of charcoal, unless they have been distilled for when prepared by smothering the fire, there is always a portion reduced to the state of ashes [braise].

2. That

2. That the anhydrous sulphate of lime, whether na sulphate of tural or artificial, and the nonanhydrous sulphate calcined, lime, contain the same proportions of lime and sulphuric acid; namely, 0.42 or 0.43 of lime, and 0.58 or 0.57 of acid, near

ly as determined by Bergman.

66

3. That the sulphate of barytes is composed of at least sulphate of barytes, 0.33 sulphuric acid, and at most 0·67 of barytes.

“4. That the mean proportions of these two salts are: mean of both these, 0.425 of lime, and 0·575 of aid, for the sulphate of lime,

and 0.065 of barytes, and 0·335 of acid, for the sulphate of barytes.

"5. And lastly, that in pure calcined sulphate of lead sulphate of there are 0.69 of metal, 0·26 of sulphuric acid, and 0·05 of

lead.

oxigen."

XII.

Extract from a Letter of Mr. GEHLEN to Mr. DESCOTILS, on the Igneous Fusion of Barytes*.

It appears to me, that the French chemists are yet un- Igneous fusion

acquainted with the fusibility of pure barytes by fire, which of barytes Mr. Bucholz discovered, and described in 1800, in the 2d number of his Beitraege zur Erweiterung and Berichtigung des Chimie.

If pure barytes be heated in a platina or silver crucible, it succeeds the liquefies in its water of crystallization. After this water is aqueous. evaporated, it enters into fusion at a bright cherry red heat, and flows like an oil. On cooling, it becomes a gray mass, radiated in its fracture, which, when powdered, redissolves in water, heating more strongly than lime, and recrystallizes in cooling.

Mr. Bucholz, having hitherto prepared his pure barytes Does not take only in Pelletier's method, did not know by experience, place with barytes obtained that barytes did not melt when it has been prepared by the by decompo decomposition of the nitrate by fire; which it might have sition of the been expected to do, but which I have never seen take

* Annales de Chemie, Vol, LXIV. p. 168.

nitrate.

place,