Lapas attēli
PDF
ePub

202

CHEMICAL EXAMINATION FOR THE DETECTION OF ARSENIC.

five minutes, gave the properties of cast-iron to a square bar of malleable iron, of -four-tenths of an inch on a side.

Wires of copper, and of alloys of copper and zinc, are increased in diameter, and diminished in density, by annealing. The operation of rolling condenses the metals more than that of wire-drawing. The density of iron and copper is greater, if the metals are heated before being passed through the rollers. The reverse is the case with alloys of copper and zinc. The density of the metals is greatest when drawn into very fine wires.

Wires may be increased in length in two ways, by a diminution in the area of their cross section, or by increasing the distances between their particles. When wires are lengthened in the manner last named, they return to their former length by annealing.

Hydrogen has an action on copper and silver, at high temperatures, which permanently separates their particles. On alloys of copper and zinc, and even of silver and copper, it has no such action.

Wires of different metals, which, after passing through the same hole in the wire-drawing plate, have different diameters, acquire equal diameters by annealing.

The diameter of a wire increases, very slowly, by time, after passing through the wire drawing plate. Wires which have been bent, and then straightened, re-acquire a curvature.

"Wires exposed to a high heat, lose a part of their tenacity. They require to be annealed in wire-drawing, not to -render them more tenacious, but to allow the particles to resume the positions from which they may again be displaced. The loss of tenacity is common to copper, iron, platinum, and the alloys of copper - and zinc.

[ocr errors]

Brass wire approaches to iron in strength, while copper is inferior to it. Brass may be used instead of iron, where the latter would oxidate too rapidly.

The iron wires are given at strengths from 79.000lbs. to the square inch to 127,600 lbs. The brass wires, from 78 to 87,000lbs. to the square inch. Copper, from 38 to 44,000 lbs. The diameters of the least and greatest wires were, iron, 014 inch, and 205 inch; brass, 070 and 267 inch; copper, 019 and 285 inch.

The finer wires bear greater weights,

in proportion to their areas, than the coarser ones, because the particles of the former are compacted through the whole cross section, while those of the latter, for a certain depth only, are thus forced together. Ann. de Chim. et de Phys.

CHEMICAL EXAMINATION FOR THE DE-
TECTION OF ARSENIC.

Sir, I am induced to send you the following particulars of an investigation I have been lately engaged in, because some circumstances were presented during the analysis which might have led to an erroneous conclusion, had they not been followed up closely; and also, because I think it desirable that, in an inquiry so important, every thing which tends to error should be pointed out as soon as possible, in order to prevent its injurious effect. Arsenic is a poison which the chemist is called upon, too frequently, to detect-many tests have been proposed, some altogether useless, and none to be absolutely depended on; not even the sulphureited hydrogen test, unless it is followed by the actual reduction of the metallic sulphuret. This will, I hope, appear satisfactory to all your readers who may be inclined to peruse this paper. The errors which I allude to are these:1st, It may happen that a green will be produced on adding to a liquid suspected to contain arsenic, sulphate of copper and an alkali, even though it should be eventually proved to have none in solution; and 2dly, sulphuretted hydrogen will occasionally give rise to a yellow appearance in a similar fluid, having every appearance of sulphuret of arsenic. But I will state my experiments in a detailed manner. A few days since I received the contents of the stomach of a young woman, who had died evidently from the effects of some metallic poison, indeed, a few hours before her death she had confessed to the surgeon that she had taken a large quantity of arsenic, still it was considered desirable that the stomach and its contents should undergo a chemical examination, it was accordingly sent to me; having, however, failed in getting evidence of arsenious in the contents of the stomach, I next proceeded to experiment on the stomach itself, which I did not receive till eight days after the death of the woman. When it was brought into my laboratory it was in a

CHEMICAL EXAMINATION FOR THE DETECTION OF ARSENIC,

state of decomposition: this circumstance rendered it probable, that there was very little arsenious acid present, since it is the property of this poison to preserve from decay the bodies of those destroyed by it. The antiseptic effects frequently extend to the whole body. The stomach and intestines of persons who have died from arsenous acid, have been found entire and firm at the distance of 12 and 20 months after death, and in some of these instances the poison was detected.-(See Edinburgh Phil. Journal, vii. 381.)

The folowing experiments were, however, made to ascertain whether any did exist in the stomach in question :

1st. Portions of the stomach which seemed in an inflamed state, and to which there were adhering minute specks of a white substance, that seemed to resemble arsenic, were detached and boiled for some time with distilled water, to the filtered solution: in three test tubes were severally added ammoniaco - nitrate of silver, ammoniaco-sulphate of copper, end bichroniati of potash; from the first a white precipitate fell down (chloride of silver), and when it had subsided, another drop of the solution of silver with ammonia, threw down a precipitate in which a tinge of yellow was perceptible; from the second a precipitate of a dull green colour fell down; and in the third no change was produced, either before or after boiling.

༄་

2. The remainder of the filtered soJution was acidulated with acetic acid, and a current of sulphuretted hydrogen transmitted through it for a quarter of an hour, it became muddy, but when the excess of sulphuretted hydrogen was driven off by boiling, no yellow precipitation ensued, even after standing some hours; and when, at the expiration of that period, it was passed through a filter, nothing remained behind, so it may safely be concluded that no arsenious acid as present: yet it will be observed that both ammoniaco-nitrate of silver, and ammo. i niaco-sulphate of copper, seemed to indicate otherwise; the former by the yellow coloured, and the latter by the green precipitation. I suspect the yellow to have been caused by the presence of some phosphate, and the green by some animal principle; the facts, however, prove Dr. Christison's views to be correct. -(See Christison on Poisons.)

3d. The stomach itself was then put into a clean saucepan, and boiled, for

203

three hours with distilled water, which was then poured off, and the stomach again digested for an hour with distilled water made a'kaline by ammonia; by this means if any arsenious acid had been present, it must have been dissolved. The watery solution was evaporated to drymess at a temperature under that of boiling water, and the solid residuum boiled for half an hour with eight ounces of distilled water: by this means, after filtering through blotting paper, a yellow and nearly clear solution was obtained, the solid matter on the filter was then washed with an alkaline liquor, and the washings added to the before-mentioned alkaline solution.

4th. A small quantity of this yellow solution was put into six test tubes: into one a few drops of weak sub-carbonate of potash was dropped, and then immediately a few drops of sulphate of copper carefully prepared and purified from iron

the liquor became of a faint blue colour, but these was not the least precipitate; into the second and third tubes, ammoniaco-sulphate and nitrate of copper were dropped, but with no result.

5th. Into the fourth test tube a little sub-carbonate of soda was added, and then boiled; afterwards a drop of nitrate of silver, a whitish brown precipitate fell down into the fifth tube, a little sub-carbonate of potash was added, and then a stick of nitrate of silver dipped in, the precipitate, as before, was whitish brown: into the sixth tube ammoniaco-nitrate of silver was dropped, this threw down a white precipitate; after this had subsided, a further addition caused no yellow, but in the course of half an hour the whole liquor assumed a pink hue, owing probably to the pressure of animal matter.

6th. Some of the liquid was put into a wine glass, and the end of a glass rod being dipped into ammonia, and the end of another into nitrate of silver, they were brought into contact just below the surface of the fluid, but no yellow appeared, when the same experiment was made with a liquid with which arsenious acid had been previously mixed, although muriate of soda was purposely added, yet the yellow arsenie of silver was distinctly desceptible, and this seeme the best manner of applying the nitrate of silver test, but it completely failed in giving evidence of arsenious acid in the present instance.

7th. Bichromate of potash was also

201

MACHINE FOR SPREADING INDIA-RUBBER UPON CLOTH.

tried several times, and under different circumstances, but with no effect.

8th. A stream of sulphuretted hydrogen was next passed through the alkaline liquor for ten minutes, and the solution evaporated to one half, having been previously f

arsenious acid been taken up by the ainmonia, it would still have remained in solution, under the form of a sulphuret, and would have passed through the filter. but the yellow sulphuret of arsenic would have made its appearance on the addi tion of an acid; nothing of the kind, however, took place, and hence it was quite evident that no arsenic was present.

9th. It now only remained to pass a current of sulphuretted hydrogen through the watery solution; it was accordingly filtered and acidulated with acetic acid, but it was found impossible to obtain a I clear liquid; the gas was, however, passed through it for twenty minutes, when the whole became of a dirty yellow colour; this yellow, I was satisfied, was not produced by sulphuret of arsenic, but in order to put the matter beyond the reach of doubt, it was and then

made strongly alkaline by ammonia: here, as before, if sulphuret of arsenic had been present, it would have been dissolved by the alkal, and the addtion of an acid would cause it to be deposited of a yellow colour; it was accordingly passed through a filter, and to the clear liquid hydrochloric acid was added: after heating for a few minutes, a flocculent precipitate gradually subsided, having a faint yellow colour; this might, by some, have easily been mistaken for sulphuret of arsenic, but when it was carefully dried a portion was burnt, and from the smell it emitted, was proved to be animal matter; and when a portion was heated in a small dry tube, with black flux, no appearance of sthlimation was observed, nor was there hit peculiar garlic odour emitted, which is always the case when arsenic is sublimed.

Thus it was safely inferred that there was not the slightest trace of arsenic either in the stomach or its contents.

I forbear from any furth r comment, trespassed too

as I shall already have if you think

much on your time,

what I have written worthy of publ eaton, you will oblige me by inserting it in your valuable periodical at your earlie t convenience.-Yours, &c.

HENRY M. NOAD.

MACHINE FOR SPREADING INDIA-RUBBER
UPON CLOTH.. PATENTED BY WILLIAM
ATKINSON, OF LOWELL, MASSACHUSETES.
947 0

The cloth, says the patentee in his specification, to be coated with India-rubber, is to be made into an endless web This

[graphic]

the dissolved caoutchouc or India-rubber, is spread upon the end ess web by the aid of a third cylinder, placed parallel to, and nearly in contact with, one of the cylinders around which the endless web passes.

I make a frame of wood; into the lower parts of this frame, uprights are mortised, which serve to support a rail on each side, leaving, however, the sills sufficiently clear within the uprights to form a railway upon which the rollers of a carriage may traverse back and forth.

Upon suitable supports, at one end of this frame, there are placed two cylinders of metal, of cast iron, of one foot in diameter, and two feet nine inches long. The axes of these cylinders are parallel to each other; around the inner cylinder the web to be coated passes; and the outer cylinder is made adjustable by means of screws, or otherwise, so that

contact with, or it may be brought into to any required distance from, the web, or cloth. These cylinders are geared together by means of toothed wheels upon their shafts.

The second, or carriage cylinder (also of metal), around which the endless web passes, is supported upon a carriage, furrishel with wheels, or rollers, which run upon the lower rails or sills. When used as a drying cylinder, it should be three feet. A windlass is placed at the back end of the frame, from which ropes pass to the eylinder ear

age, serving, by means of a winch, to draw the carriage, so as to render the cloth taut. Steam is to be admitted into the eyfinder through a hollow gudgeon.

In order to apply the solution to the cloth, &c., and to confine it to the proper width, we fit two cheeks, or pieces of wood or metal, so as to rest upon the two contiguous rollers, one at or near each of their ends, and these, when in their places, convert the rollers into a trough, or hopper, for contains ing the solution. The distance of these pieces from each other is regulated by attaching them together by means of a frame, or rod, at their upper sides, so that they may slide, and be affixed in their places by thumb screws, or otherwise.

To prevent the eloth adhering to the outer roller, among other methods, wet sponges or brushes may be laid along it.

[subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][ocr errors][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed]

205

REPORT OF EXPERIMENTS MADE BY THE COMMITTEE OF THE FRANKLIN INSTITUTE
OF PENNSYLVANIA ON THE EXPLOSIONS OF STEAM-BOILERS, AT THE REQUEST OF
THE TREASURY DEPARTMENT OF THE UNITED STATES.

1

(From the Journal of the Franklin Institute.)

(Concluded from p. 190.)

Plate VI. Fig. 1.

[graphic]
[ocr errors]
[blocks in formation]

REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STEAM-BOILERS.

Plate V. Fig. 2.

Pressures,

[graphic]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
« iepriekšējāTurpināt »