Imatges de pàgina
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sol via A this precipitate in alcohol and cry stalling, narcotine was deposited, the other bases remaining in solution; and Dr. Anderson imagined that thia solution contained a base which had not as yet been noticed. The original mother-liquor from which the ammonia precipitate had been separated still contained bases, which might be extracted by agitating with ether. From the etherial solution meconine could be obtained. The products of decomposition of narcotine under the action of reagents were very interesting. The composition of this alkaloid had been determined by different experimenters, and their results did not altogether agree; for the three formulae, CltH23NOu, CwH25NOu, and C^HjjNO,,, had been given, which had been explained by the supposition that there existed three alkaloids agreeing very closely in their properties, and named methylo-, cthylo-, and propylo-narcotine, on account of the decomposition they underwent when passed over soda lime, the three yielding respectively methylamine, cthylamine, and propylamine. By the action of oxydising agents, narcotine might be separated into a basic substance called cotamine, Cjjhunoj, and an indifferent bony, which was meconine; three acids being produced at the same time,—namely, opianic acid, C20Hl0O10, hemibanic acid, C^H^O,,, and a third acid body of the composition C20H10O8. Cotamine, when acted on by nitric acid, gave an acid containing C16H,N09, called apophyllic acid. This acid might be considered as compounded of methylamine and an acid of the formula CuH.fi uand, in fact, when boiled with potash, underwent decomposition, giving off methylamine. On dissolving narcotine in dilute suphuric acid, and exposing it in sealed tubes to a temperature of 3000 F.. crystals are seen to form, which contain meconine; colouring matter and a humic substance being formed at the same time, while the solution is found to contain cotarnine. When opianic acid is mixed with concentrated sulphuric acid, a purple liquid is produced, which on dilution furnishes a reddish colouring matter which has the properties of alizarin. "With regard to the composition of the various substances found in opium, some relation between the different bases might be discovered. Codeine was homologous with morphine, as far as the formula was concerned; but this relation was not borne out by the properties of the two bases, which were very different. The other bases also showed, in some eases, a relation in composition. Several of these alkaloids, when exposed to the action of nitric acid, gave rise to substitution products. The substitution product of codeine could only be prepared by employing a very dilute acid; if stronger acid were used, a resinous acid was obtained, which, when boiled with potash, gave rise to a volatile base. This last reaction was very common among the group of alkaloids. With regard to the variations in the relative proportions of the various bases contained in opium, that obtained from China contained a large amount of narcotine and very little morphine; while the opium from Egypt contained scarcely any meconic acid, its place being taken by sulphuric acid.

Mr. Foster said that from the experiments that he had made in conjunction with Dr. Matthiesson, it appeared that the composition of cotarnine was represented by the formula C^H^NOj, so that cotarnine and meconine together exactly made up narcotine. They had found that the oxidation of meconine furnished an acid containing Cjuh^o,,,. The action of sodium amalgam on narcotine furnished a basic substance, which appeared to be cotarnine. This reaction was interesting, because it was the reverse of the action of nitric acid, which also gave rise to cotarnine. They represented cotarnine by the rational formula

[ C2H° J N> for ihe uction of nitric acid on this body furnished an acid of the formula C2.,H12O10, and on dissolving cotarnine in hydrochloric acid and heating, a decomposition ensued, chloride of methyl and a body of the formula C„Hi3N06,HCl being formed. From their

experiments on the decomposition of narcotine by soda lime it appeared that under these circumstances trimethylamine was formed, which had been mistaken for propylamine on account of its platinum salt containing the same per-centage of metal.

Dr. Rkdwood remarked that he entertained doubts as to the absence of meconic acid in a genuine sample of opium. He had invariably found it to be present in a great number of samples which had come under his noticeMr. Morson observed that meconic acid was always present in opium, unless it had been removed by lime or a similar agent.

MISCELLANEOUS.

Cbrmical Society-—The next Meeting of this Society will be held on Thursday next, the 15th instant,

Recent Improvement* in Lucifer SEatche*.—

Of matches prepared witli ordinary phosphorus, and which consequently ignite readily upon any friction surface, the *' Patent Paraffin Matches" of Messrs. Letchford and Co. are particularly good examples. Iastead of the objectionable sulphur coating, melted paraffin is used for impregnating the wood and rendering it more inflammable. Such matches are not likely, therefore, to play havoc with the silver candlesticks and bright metallic surface! often brought near them in actual service. Their power of remaining uninjured by damp is a special character for which this kind of match is remarkable; in a comparative examination of several different sorts, these only were capable of being ignited alter 6ix hours' exposure to a moist atmosphere. On this account they would be particularly suitable for export, and little affected by climate Action of Bronietnvlene on Strychnin*.— The compounds resulting from the action of bromethylene on strychnine are described by Menetries {Bulletin de St. Petertburg, t. iv. p. 570). The two bodies were heated in a glass tube placed in a water-bath at 1 oo° for a quarter of an hour. A little spirit of wine is added to facilitate the reaction. A glistening white mass is left in the tube, which is distilled to remove uncombined bromethylene and spirit of wine. A fluid remains in the retort, from which crystals separate on cooling. The crystals are slightly soluble in cold, and very soluble in hot water and alcohol. Their solution gives no precipitate with alkalies. With sulphuric acid and an oxidizer they give the same colour as strychnine. With nitrate of silver they give a precipitate ol bromide of silver; but analysts proved that only half of the bromine was precipitated; the whole could only be removed by digesting with moist silver oxide. The analysis of the crystals led to the empirical formula CM H20 N2 Ot B22. The author examined other compounds of strychnine with nitric acid and chlorine, and those resulting from treatment of the bromine compounds with nitric acid, and describes several new bodies.

ANSWERS TO CORRESPONDENTS.

Downing v. Chattee.—We can insert no more communications on this subject

F.R.S.—"Tour library at Burlington House ought to contain the work. See Vol. vli. p. j]8.

M. A. R Qutriu.—Received.

Tkomat 0.—Tno letter bas been forwarded to the person named in it. You will most probably receive a reply by p<«t.

A Manufacturer.—An advertisement in our columns would moet likely briun oevoral applications for the situation.

Futd't Oyroecope.—Can any correspondent kindly refer us to the original puper on this subject?

E. Sherratt.—The mineral occurring in the form of thin crystalline layers between the seams of coal in the Eart Granville's i^t, was found by analysis to consist of the carbonates of iron, lime, and raojruesia. It is remarkably compact in structure, entirely soluble iu aads, and contains the whole of the iron in the lowest state of oxidation.

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NOXIOUS AND OFFENSIVE VAPOURS. The motion carried by Lord Derby last Friday night, for a Select Committee of the House of Lords to inquire into the injury resulting from noxious vapours evolved in certain manufacturing processes, is of too much importance to a great number of our readers to be allowed to pass without notice. Lord Derby introduced the motion by a remarkably temperate speech, in the course of which he showed that he was well up in the chemistry of Leblanc's process, as well as aware of the extent of our soda trade; and he therefore expressed himself laudably anxious that nothing should be done to seriously interfere with so important a branch of industry. With regard to the evolution of hydrochloric acid gas, against which, we presume, the inquiry is principally directed, and from which Lord Derby himself seems to be a sufferer, that, we think, may be easily disposed of. The escape of this gas, besides being •wasteful, is easily prevented. It has been prevented in many manufactories, and might be in all. A condensing tower ought to be erected in every factory, and the subsequent disposal of the acid must be regulated according to circumstances.

It may be urged by some that the remedy at common law is already quite sufficient to prevent a nuisance; but this, however, does not appear to be the fact. In any case, this remedy must be eminently unsatisfactory to manufacturers. We have seen recently that when they have taken every precaution, it leaves them quite at the mercy of wonderful chemists, endowed with marvellous vision, who see bluish vapours rise whenever they place en the ground, within sight of a soda factory, a piece of ffltering-paper soaked in ammonia. Now, a certificate from a Government Inspector that the works were properly constructed and carried on, would, we imagine, he a satisfactory answer to all actions like that against "the Messrs. Chance; and so far the manufacturers would certainly benefit by being placed under inspection.

As regards the pollution of streams by arsenic and I other poisons, to which Lord Derby also alluded, there is no doubt that this also may be easily prevented; and it would probably save a good deal of litigation if the works where such a result was likely to happen were also placed under inspection.

But there are some cases in which it is difficult to see how the escape of some noxious vapour—a rather comprehensive expression—is to be entirely prevented; and it behoves manufacturers and smelters to watch well the proceedings of the Committee, and to scan warily the measure which may be introduced into the House of Lords founded on the report, to see that practical impossibilities are not required of them.

_ It is almost to be regretted that Lord Eavensworth did not succeed in adding the word "offensive" to the original motion; for although there might be more difficulty in completely destroying the nauseous stinks

emitted from factories where animal matter is burnt or dealt with, there is no doubt that the use of very simple means would go far towards mitigating the nuisance. The motion, as it stands, however, leaves ample room for the sanitarians to urge the claims of health; and as the Committee proceeds with the inquiry, the objects may perhaps be a little extended.

We have warned manufacturers to be on their guard, and we may conclude with a word to many ingenious readers who may possibly be provided with schemes to abate the evils of which Lord Derby complains. To all such the Committee will give a patient hearing, and we advise them to lose no time in bringing forward their plans.

SCIENTIFIC AND ANALYTICAL
CHEMISTRY.

Sulphide of Arsenic in Commercial Sulphide of Antimony, by R. Reynolds, F.C.S. A FEW months since I received a small quantity of powdered black antimony for analysis, being informed that several calves had died after its administration, the animals had been dead some weeks, that the only sources of evidence were the medicine itself, and such facts as had been observed with respect to symptoms. After reporting the analysis, the following outline of the case was supplied to me; but as it occurred at a distance, and I was not directly in communication with the owner of the calves, it is not quite so full as it might otherwise have been.

To each of twenty-four yearling calves was given one ounce of powdered black antimony, in a horn of urine. This was at 9 a.m., and the same evening one calf died, the whole of them being seriously ill. At varying intervals up to ten days, further deaths occurred, until ten animals had succumbed. The others ultimately recovered. The symptoms were great cramp, constipation, and falling off of the hair. In two cases postmortem examinations were made, and great irritation of the mucous coats of the stomach was found.

Analysis.—The powder was boiled with water, but neither arsenic nor any other matter was dissolved. To determine the sulphide of arsenic present, the process of Wackenroder was adopted (Fresenius). Twenty grammes are deflagrated with forty grammes of nitrate of potash and twenty grammes of carbonate of soda, by projecting the mixture gradually into a red-hot Hessian crucible. The resulting mass is lixiviated with water, filtered, the filtrate acidulated by hydrochloric acid and sulphurous acid added, after which sulphuretted hydrogen is passed through it. The moist precipitate is digested with carbonate of ammonia, filtered, acidulated, and precipitated as tersulphide of arsenic. This method is not rigidly accurate, as traces of either sulphido of antimony or of free sulphur may contribute to give too high results.

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I give below the results obtained with four distinct specimens of sulphide of antimony:—

No. i contained sulphide of arsenic 1-33 per cent.
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Thus it appears that No. 1 (that given to the calves) contained far more arsenic than did some other specimens, amounting to 5-84 grains of tersulphide in an avoirdupois ounce, being the dose which proved fatal.

The dose of black antimony may be considered unreasonably large, but I know of no grounds for supposing that the antimony produced the mischief. Large doses of this substance are constantly given to animals. Pereira speaks of doses of two to four ounceB being given to horses, and of half an ounce taken by a man for several days without bad effect.

It appears, then, that the arsenic present was the cause of mischief. The dose of pure sulphide of arsenic has not been determined, and it has often been regarded as comparatively inert. This is doubtless correct as long as it retains its insoluble condition. Medicina non at/nut nisi soluta. But, singularly enough, in selecting urine as a vehicle for dosing the calves, their owner was providing for the solution and prompt absorption of the sulphide of arsenic. When it was dissolved by the ammoniacal urine, its poisonous properties would probably be just as great as those of a similar quantity of arsenious acid in solution.

Gmelin gives a process for purifying commercial black antimony from arsenic by digesting the powder with twice its weight of aqueous ammonia for forty-eight hours with stirring, then filtering, and washing the product, which is almost entirely freed from arsenic. This method may become of some practical importance. One of the principal makers of emetic tartar informs me that the black antimony lately in the market has been much more contaminated by arsenic than was formerly the case, and that it causes much trouble with the motherliquors.

Impurity may exist to a much greater extent than that now recorded. Thus, Gmelin quotes Scrullas to show that all German and French black antimony, excepting that of Montlucon, contains from i-6 to 5-0 per cent, of arsenic.

It is evident that those who may unwittingly vend the contaminated samples incur the risk of being held responsible for results.

80 long as sulphide of arsenic is present, and its noxious or innocuous quality depends upon the nature of the fluids with which it meets in the stomach, there will be a very disagreeable uncertainty about the use of the crude drug.—Pharmaceutical Journal.

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cientlv pure for use in the arts. The author has adopted the following modifications of this process:—First, change carbonate of potash into caustic potash by means of lime; make one atom of potash act on one atom of nitrate of soda, and evaporate the liquid to 400 Baume. This liquid, when cold, furnishes a first crystallisation of nitrate of potash. Repeat these evaporations and crystalisations several times. Drain, and wash the crystals of nitrate of potash in water acidulated with a little hydrochloric acid, and the caustic soda separated from, the crystals is, according to the author, transformed into Seignette salt.f The chief advantage of this process is the larger quantity of nitrate of potash it produces, this Bait being much less soluble in a solution of caustic soda than in a solution of carbonate of soda. Moreover, the concentration can be carried to a greater extent, because caustic soda is uncrystollisable.—Kepertoire de Chemie, iv. 42.

On Peruvian Guano, by M. Liebio.

Almost all the guano now so extensively used in Europe is obtained from the New World. Th'<-»natural manure, composed essentially of urate and oxalate of ammonia, phosphate and oxalate of lime, and a peculiar base, guanine, is, it is well known, the produce of certain sea birds.

M. Liebig, whose works have rendered so much service to agriculture, has recently published a Memoir, in the Annalen dcr Chemie und Pharmacie, vol. cxix. p. n, 1861, which to us appears to throw great light on the cause of the fertilising properties of guano, and on the means of appreciating them by the aid of chemical analysis.

The manifest action of Peruvian guano on the soil has not hitherto, ho says, been satisfactorily explained. The good effects of this manure are generally attributed to the large proportion of nitrogenised matters which it contains,—matters consisting chiefly of ammoniacal salts and uric acid. Many observations, however, have proved that a field manured with guano yielded an abundant crop, while the addition, to a part of the same soil, at the same time, and for the same crop, of a quantity of ammoniacal salts corresponding exactly, in richness with nitrogen, to the guano employed, had scarcely any effect on the crop.

If, in the first instance, guano owes its fertilising properties to the nitrogen it contains, it is diflicult to comprehend why, in the second instance, the same quantity of nitrogen, added to the soil in its most active form, should have no influence on the crop. The cause of the energetic action of guano must then be sought in its other constituents. If from these we except uric acid, the influence of which on vegetation is almost completely unknown, thero remain only earthy phosphates and alkalies, which, existing simultaneously with ammoniacal salts, might communicate to guano its active properties.

According to M. Liebig, various reasons prevent the acceptance of this conclusion. Phosphate of lime is, with ammoniacal salts, the predominating clement of Peruvian guano, which contains 3* to 36 per cent, of it. A quantity of phosphate (powdered bones), four, six, or even eight times larger than that contained in guano, is very far from producing the effect of the natural manure; its fertilising action is frequently increased by the addition of ammoniacal salts, but the results fall far short

t For largo quantities of Seignette salt prepared in this way

there would Do no use. It would bo better to pass a current of c*r

l boaiQ add into the liquid to transform the sods into carbonate.—fl. K.

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of those produced by guano containing phosphates in the same proportion. The principal difference to be remarked between these two manures consists in the length of time each takes to manifest its action,—a point which has hitherto remained unexplained. The influence of guano is apparent the first year, often even after a few weeks, and goes on diminishing year by year; the powdered bones, on the contrary, act feebly during the first season, but afterwards their effect increases.

These facts once established, we will adduce M.Liebig's experiments, which tend to prove that guano owes its rapid action to the presence of oxalic acid.

Various kinds of guano contain very varying quantities of oxalic acid,—another proof that the composition of guano is not constant. Certain analyses, not indeed sufficiently numerous to lead to a positive conclusion, seem to prove that the quantity of oxalic acid contained in a sample of guano is in inverse proportion to the weight of uric acid it contains; that is to say, that the guanos rich in uric acid are generally poor in oxalic acid.

If Peruvian guano is moistened with either cold or boiling water, and filtered immediately after, the liquid furnishes, by evaporation, abundant crystals of neutral oxalate of ammonia, the mother-water containing a certain quantity of phosphate and sulphate of ammonia.

If guano is moistened with cold water and left alone fur some time, the results are very different. The proportion of oxalic acid contained in the solution goes on diminishing, and the filtered liquid contains phosphoric instead of oxalic acid. After remaining in contact for twenty-four hours, the quantity of phosphoric acid becomes so considerable that the filtered liquid, boiled with sulphate of magnesia, yields, without the addition of ammonia, an abundant crystalline precipitate of phosphate of magnesia and ammonio-magnesian phosphate.

It is easy to explain why phosphoric acid, under these circumstances, should become soluble; in fact, it is evident that the oxalate of ammonia, dissolved by the addition of water to the guano, is gradually transformed in presence of phosphate of lime, and that the result of the reciprocal action of these two salts is insoluble oxalato of lime and soluble phosphate of ammonia.

It will be seen from this that the phosphoric acid of guano is not dissolved, because the manure contains at the same time oxalic acid; for by distributing all the fixed bases of the guano between phosphoric acid, sulphuric acid, and chlorine, there remain for the phosphoric acid only two equivalents of lime and magnesia, forming with it a salt partially soluble in neutral salts of ammonia. The presence of oxalic in the aqueous solution of guano is a sufficient reason for the absence of lime.

The following fact seems to contradict the explanation given above:—liecently-precipitated phosphate of lime, with two or three equivalents of base, is scarcely at all modified by long contact with oxalate of ammonia; traces only of phosphoric acid are found in solution. But it must he observed that guano always contains a body which facilitates decomposition, sulphate of ammonia. This_ salt renders the phosphate of lime partly soluble, but it does not pass into the solution in this form, the lime being immediately precipitated by the oxalic acid, the action of the sulphate of ammonia being prolonged, and the decomposition of the phosphate of lime goes on. By adding a small quantity of sulphate of ammonia or a few drops of hydrochlorate of the same base to a mixture of oxalate of ammonia and phosphate of lime, the phosphate is very rapidly changed into oxalate.

In guano moistened with water the transformation of oxalate of ammonia to the state of phosphate goes on rapidly to a certain point, after which the action slackens, and the decomposition is incomplete even after eight days. A little oxalic acid always remains in the liquid, easily recognisable by the fact that the precipitate which it gives with a salt of lime does not entirely disappear in acetic acid. The persistence of the oxalic acid is perhaps due to the fact that the phosphate of lime, not yet decomposed, is masked in a thick coating of oxalate of lime, which considerably retards the action of the oxalate of ammonia.

By acidulating with sulphuric acid the water serving to moisten the guano, so as to render the mixture freely acid, the decomposition becomes so much accelerated that it is finished in a few hours. No trace of oxalic acid is then found in the liquid, but in its stead an equivalent quantitv of phosphoric acid.

Acetic acid and water charged with carbonic acid act on guano in the same manner as sulphuric acid.

M. Liebig has obtained the following results from a specimen of guano remarkable for the small quantity of oxalic acid and the large quantity of uric acid (18 per cent.) it contained. Besides water, potash, soda, and ammonia, he found in the aqueous extract of 100 parts of guano:—

Phosphoric acid . . 1-857
Oxalic acid . • 4*20*

Sulphuric acid . • 3*371

After having effected the transformation of the phosphate of lime by a little sulphuric acid, M. Liebig found that 4*2 per cent, of oxalic acid contained in this guano had been replaced by 3 per cent, of phosphoric acid; that is to say, that by this method about half of the whole of the phosphoric acid of the guano had become soluble.

In other kinds of guano the same method has rendered soluble a weight of phosphoric acid corresponding to 10 or 12 per cent, of tho weight of the guano; in other words, the whole of the phosphoric acid contained in the guano.

M. Liebig devotes the latter part of his Memoir to examining the practical conclusions to be drawn from these facts. When, he says, a field manured with guano receives too little rain to moisten the manure mixed with the arable land, all conditions are united to favour the solution of a certain quantity of the phosphoric acid, combined with the lime, and, consequently, to increase the fertilising action of the ammonia. The guano then acts in the same manner as acid phosphate of lime.

Heavy and continuous rains, while washing the soil, disturb this decomposition; and it is to be desired, for the interest of science, that agriculturists would give some attention to tho influence of guano, under these various circumstances, on the fertilisation of the soil.

It is hardly necessary to remark that the action of guano can be made certain—at least, so far as it depends on the reaction of oxalio acid on phosphate of lime—by moistening the manure before using it with very diluted sulphuric acid, and then letting it stand for twenty-four hours. The moistened mass should have an acid reaction.

The addition of water, to increase its weight, is the most common falsification of guano; the greatest inconvenience arising from this fraud is, that it favours the decomposition above mentioned. The evaporation of ammonia proceeding from the phosphate of ammonia, formed under the influence of water, explains the loss of nitrogen observed in guano which has been kept for any length of time.

It is now evident that the agricultural value of guano

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has been but imperfectly appreciated, when the ammonia, phosphoric acid, and phosphate of lime which it contains, have been estimated without taking account of the oxalic acid, to which, as M. Liebig has shown, its fertilising action is chiefly due.

This account would be incomplete without a description of the simple process by which M. Liebig estimates the oxalic acid in guano. 1 he following is an extract from his letter on the subject:

"To estimate the oxalio acid, I boil the guano with nitric acid; I then wash it; afterwards I add hydrochloric acid to the residue, which dissolves the remaining oxalate of lime and phosphate, leaving the. urio acid. I neutralise the acid liquid with ammonia, which precipitates the phosphate and oxalate; I then add acetic acid, which dissolves the phosphate of lime, and throw the oxalate on a filter, wash it, &c."

Guanos can thus, in a very little time, be tested before being used.— Condensed from the Annalen der Chemie und Pharmacie, cxix. 11.

PROCEEDINGS OP SOCIETIES.

ROYAL INSTIT0T1ON OF GREAT BRITAIN.

Weekly Evening Meeting, March si, i862.

The Rev. John Barlow, M.A. F.R.S., Vice-President,

in the Chair.

A Lecture, by F. A. Abel, Esq., F.R.S., on Some of the Causes, Effects, and Military Applications of Explosions. The contrast presented by lectures delivered on consecutive Friday evenings in this theatre is often very remarkable, and there certainly can be none greater than that which will be afforded by the eloquent discourse to which we all listened with such pleasure on last Friday, and the very matler-of-fact story which I am about to tell this evening. An imperfect sketch of the causes, effects, and some of the applications of one large class of explosions, is all that I have to offer to the members of the Royal Institution and their friends on this occasion; but, as one who is now rarely called upon to lecture, and whose time is almost exclusively devoted to pursuits of a purely technical character, I feel that I may claim some amount of indulgence on the part of my audience; and, for the very elementary character of much of my discourse, I trust that the desire which I have to render as clear as possible the description which I shall give of some of the military applications of explosions, will be a sufficient apology.

The phenomena which we are in the habit oi classing under the term explosions, are all due, I need scarcely Bay, to a sudden and considerable expansion of matter. The successful effort, for example, of confined particles of air to escape from the bonds within which they have been compressed, and to re-assume the position which they originally occupied relatively to one another, is always accompanied by the production of sound, the violence of which is regulated by the extent and suddenness of the expansion and the amount of resistance to be overcome, and, consequently, by the violence with which the particles of air dash against and impart vibration to the surrounding atmosphere, or other particles of matter with which they come into collision ; as is the case when I compress air within this bladder, until a point is reached at which the cohesive lorce, holding the particles ot the bladder together, is overcome by the pressure exerted from within, and we have a sound produced. [This was illuslrated by air being forced by a syringe into a small india-rubber balloon until the pellicle burst with a Blight report.] What we call c xplosions may also be produced by a sudden or very rapid

conversion of a solid or liquid into a gas or vapour,—by the sudden change of state (as we commonly call it) of matter, brought about by the action of heat, which is therefore one great—in fact, the most important—source of explosions.

Such explosions as are due solely to physical agencies, afford for consideration a number of points of interest; but it is impossible to treat the whole subject of explosions generally in one lecture. I must therefore ask you to allow me to confine myself to the consideration of those explosions which are brought about directly or indirectly by chemical agency.

When chemical action produces, or is followed by, an explosion, we know that the main cause of that explosive effect or result, of which I have just endeavoured to point out the general nature, is the development of heat consequent upon the disappearance of chemical activity; and we also know that the amount of heat—if I may use this term in speaking of such an agency as heat—corresponds to the energy of the chemical action; just in proportion, therefore, as we have chemical energy exhibited, we have heat developed. There is another cause to which we may refer the production of explosions, and that is the alteration in the state of matter resulting simply from chemical change. Solids may, as you all know, be, under these circumstances, converted into vapours or gases; such changes may he effected very suddenly, and quite independently of any heat developed; and the sudden expansion thus brought about would naturally produce the effect of an explosion. We may readily conceive that, if a small quantity of powder, such as the charge used in a small arm or rifle (weighing about seventy-five grains), were suddenly converted, independently of the action of heat, into a considerable volume of gas, an explosive effect would be produced. But, accompanying this change of state, we have, in the actual case of the explosion, very intense heat developed, resulting from the chemical transformation; and that heat, by its expansive effect, contributes far more to the production of the violent explosion than the mere alteration of state resulting from the chemical change. This may readily be rendered evident by comparing the volume of gas which, by theory, would be produced by ignition of the powder, taking into consideration the expansive action of the resulting heat, with the comparatively small volume which the Ros would occupy at common temperatures. [The difference in volume of the charge of gunpowder and other gases produced under the above circumstances was illustrated by means of cubes.]

Now, there are several classes of chemical action by which explosions may be brought about. Firstly, we are acquainted with a few instances in which explosions result from chemical combination, as in the case of some elementary bodies which possess a tendency to enter into combination with great energy, and consequently with explosive violence. There are numerous instances of combination of a very energetic character, especially between compound bodies, but very few of them, indeed, produce explosive results, simply because the combination proceeds in comparatively a gradual manner. As I hare said before, it just depends upon the rapidity of action we can establish between bodies,—upon the intensity of chemical affinity exhibited by bodies when they are brought together,—whether we produce a sufficiently sudden expansion of matter to bring about an explosion. In a cose of feeble chemical action, such as that of an acid upon a weak base, heat is developed, but slowly and to comparatively a slight extent, because of the very gradual nature of the combination. Thus, if we dissolve this oxide of zinc, which is a weak base, in acid, the heat developed will only gradually melt the very fusible material with which this vessel is coated. This is an example of feeble chemical action. If we proceed a step further, taking, for example, such a substance as this

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