portion of water contains 29 of oxygen with 3.8 of hydrogen. There is present, therefore, exactly the quantity of oxygen which the metal requires to combine with the acid; and no water remains above this; or it may be illustrated under another point of view. Muriatic acid gas is composed of oxymuriatic gas and hydrogen. A metal acting on it must attract the oxymuriatic acid-that is, the muriatic acid and oxygen, and liberate the hydrogen. No water, therefore, ought to appear more on this theory than on the other; but the real products in both must be a dry muriate, or chloride, and hydrogen gas. In the action of ignited metals on muriate of ammonia, it is equally evident, on the same principle, that no water ought to be obtained. How then is the production of water to be accounted for?

Though the water obtained in these experiments cannot be derived from hygrometric vapour in the gas, there is another view under which it may be regarded at present as an adventi tious ingredient. The acid having a strong attraction to water, may be supposed in the processes in which it is usually prepared, to retain a portion not strictly essential to its constitution as muriatic acid gas, but still chemically combined-that is, combined with it with such an attraction as to be liberated only when it passes into other combinations, and it may be this portion which is obtained in the action of metals on the gas; the other portion, that essential to the acid, being sufficient to produce the requisite oxidation of the metal.

The question with regard to the existence of water in this state, Gay-Lussac and Thenard have already determined. From an extensive series of experiments, they found reason to conclude, that muriatic acid gas, in whatever mode it is prepared, is uniformly the same. From the quantity of hydrogen gas which combines with oxymuriatic gas in its formation, it follows that it contains 0.25 of water essential to its constitution. But the gas obtained by the usual processes, afforded, they found, exactly 0-25 of water, when transmitted over oxide of lead, or combined with oxide of silver; and the same compounds are formed as by the action of oxymuriatic acid on silver and lead in their metallic state. They prepared muriatic acid gas, by heating fused muriate of silver with charcoal moderately calcined. It contained just the same quantity of water as muriatic acid obtained from humid materials, as it afforded the same quantity of hydrogen from the action of potassium. And instead of being capable of receiving the smallest additional portion of water, a single drop of water being introduced into three quarts of it, did not disappear, nor even diminish; but, on the contrary, increased in volume. These facts establish the conclusion, that muriatic acid gas can receive no additional portion of water but that which is essential to it, and hence preclude the solution of the

Recherches Physico-chimiques, tom. ii. p. 133.

difficulty under consideration by the opposite assumption. And it is to is to be remarked, that should even such a portion of water exist in the gas, it cannot be supposed that the acid should carry this with it into its saline combinations, and retain it so that it should not be expelled by heat. It cannot be supposed to exist, therefore, in muriate of ammonia thus heated, and, of course, ⚫ cannot account for the water obtained by the action of the metals on this salt.

When it is proved that no extrinsic water exists in muriatic acid gas, there remain apparently only two modes on which the production of water can be explained, either that the metal may require less oxygen than is supposed in combining with the acid, so that a portion of water will remain undecomposed to be deposited, or that the oxide attracts more real acid, so as to liberate a larger proportion of water. The first of these suppositions is improbable, from the consideration of the law which regulates the combination of metallic oxides with acids; that the quantity of acid is proportional to the quantity of oxygen, so that if an oxide were formed in these cases at a lower degree of oxidation, it would only combine with a proportionally smaller quantity of acid, and the quantity of water detached from the combination would be the same.

No improbability is attached to the second supposition; and it has even some support from the consideration that many metallic saline compounds form with an excess of acid, and that it is difficult, with regard to a number of them, to procure them neutral. Metallic muriates, with excess of acid, seem in particular to be established with facility. And although an excess of metal be present in the action exerted on muriatic acid gas, this may not prevent the formation of a super-muriate, more especially as the excess is in the metallic form, and exerts no direct action, therefore, on the real acid.

To ascertain if a super-muriate were formed in these cases, the product obtained from the action of the muriatic acid on the metal was raised to a heat as high as could be applied without volatilization, so that no loosely adhering acid might remain, and the air in the retort was repeatedly drawn out by a caoutchouc bottle. The solution from the residue both of iron and zinc was very sensibly acid. Some fallacy, however, attends this, from the circumstance that the liquid state is necessary to admit of the indications of acidity; and in adding water to produce this, a change occurs in the state of combination in a number of the metallic muriates; a supermuriate being formed which remains in solution, and a submuriate being precipitated, so that the acidity of the entire compound cannot justly be inferred from that of the solution. I found accordingly, that on adding water to the product from the action of the acid gas on zinc this change occurs; a little of a white precipitate being thrown down, while the liquor remained acid. But the fallacy can be obviated,

by adding only as much water as produces fluidity without subverting the combination. Portions, therefore, of the residue were exposed to a humid atmosphere, until by deliquescence liquors were formed transparent without any precipitation; and these were strongly acid, reddening litmus paper when it was perfectly dry and warm. I further found that the product of the solution of zinc in liquid muriatic acid, when digested with an excess of metal and evaporated to dryness, afforded by deliquescence a liquor sensibly acid; and in both cases, even when the solid product was retained liquid by heat, acidity was indicated by litmus paper. Lastly, what is still less liable to objection, the residue in the experiment of heating the muriate of ammonia with the different metals, afforded similar indications of acidity. These results appear to establish the production of a supermuriate in the action of these metals on the acid, and this accounts for the appearance of a portion of water, since, supposing water to exist in muriatic acid gas, the quantity combined with that proportion of acid which would establish a neutral compound is the quantity required to oxidate the metal to form that compound; and if any additional portion of acid enter into union, the water of this must be liberated, or be at least capable of being expelled.

It was of importance, in relation to this question, to ascertain the quantity of hydrogen obtained from a given quantity of muriatic acid gas; for if the whole water essential to the acid is decomposed by the action of the metal, half the volume of hydrogen ought to be obtained, muriatic acid gas being composed of equal volumes of oxymuriatic gas and hydrogen gas. I made this repeatedly the subject of experiment by heating zinc and iron in muriatic acid gas. There are difficulties in determining the proportion with perfect precision; but the quantity of hydrogen always appeared to be less than the half; and on an average, about 12 measures were obtained, when 30 measures of the other had been consumed, a result conformable to the liberation of a portion of the combined water of the gas.

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Whether the production of water in these experiments is satisfactorily accounted for on the cause now assigned, may be subject of further investigation. In the sequel I shall have to notice another principle, on which, perhaps, it may fall to be explained. Whether accounted for or not, it is obvious that the fact itself is not invalidated by the theoretical difficulty; and also, that in relation to the argument with regard to the nature of muriatic and oxymuriatic acids, it remains equally conclusive. In the doctrine of the undecomposed nature of chlorine, muriatic acid gas contains neither water nor oxygen, and the metal employed certainly contains none. These are the only substances brought into action, and it is impossible that water should be a product of their operation. On the opposite doctrine, water is held to exist in muriatic acid gas to the amount of 4th of its

weight; and it is conceivable that by some exertion of affinities, a portion of it may be liberated. If we were unable to explain the modus operandi, this would remain a difficulty no doubt, but not, as in the opposite system, an impossible result.

"

It is to be admitted, indeed, that in none of these cases is the entire quantity of water which must be supposed to exist in muriatic acid gas obtained; and so far the proof is deficient. But neither from the nature of the experiments is this to be looked for; and I give more weight to the argument from having always found certain portions of water to be procured; while on the opposite doctrine there should be none. In those cases where, supposing water to be present in muriatic acid gas, it ought to be obtained in the full quantity, it uniformly is so, though the proof from these is rendered ambiguous by the result being capable of being explained on a different hypothesis. (To be continued.)

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ARTICLE VI.

Contributions towards the History of Anthrazothionic Acid, disco vered by Porrett, and called by him Sulphuretted Chyazic Acid. By Theodor von Grotthuss.*

Sect. 1; Choice

Sect. 1, Choice of the Name.-The name which Porrett has given to this acid is formed from the first letters of the names of the elements of which it is composed, namely, carbon, hydrogen, and azote. As the object undoubtedly must have been to bring to the recollection those constituents of the acid about which no doubt exists, and as the name given by Porrett was unsuitable to the idiom of all other languages except the English, it was natural to endeavour to correct the want of euphony of the term by alterations which should still recall the elements of which the acid is composed. In Germany accordingly the term sulphuretted prussic acid (schwefel-blausäure) was pitched upon; but this name is admissible only on the supposition that Porrett's assertion that this acid is a compound of prussic acid and sulphur be true. But from the experiments which I am going to relate, it will be seen that it contains indeed the elements of prussic acid, but in different proportions; and that neither prussic acid nor cyanogen as such exist in it. Hence the last term cannot be applied to it with more propriety than the first term.

resolved, therefore, instead of Porrett's name, to compose the term anthrazothionic acid (anthrazothionsäure) from the Greek, indicating accurately the constituents of which this acid

*!! • Translated from Schweigger's Journal, xx. 225. (Published in Dec. 1817.)

A

is composed; and I hope that the term will be adopted by chemists. It is composed of abbreviations of the Greek words. avepas, charcoal, acon, azote, and besov, sulphur. As this acid contains no oxygen, but hydrogen (as is sufficiently established by Porrett's experiments); and as it appears from my experiments and from those of Porrett that when exposed to the action of the Voltaic battery its sulphur separates at the positive pole, but its hydrogen with its other constituents makes its escape in a gaseous form at the negative pole, it follows that it must be considered as a hydracid. With respect to the name hydracid, two remarks must be made. 1. In the hydracids, and consequently in anthrazothionic acid, it has been shown that the hydrogen acts the same part that oxygen does in other acids, and that it is substituted for it. 2. At present no other acid is known composed of anthrazothion (carbon, azote, and sulphur) and oxygen. I have not been able indeed to obtain the principle, to which I give the name of anthrazothion, in an isolated state; but I conclude from analogy with cyanogen, and from various other reasons to be stated below, that it exists at least in a state of combination. From this non-existence of a combination of anthrazothion and oxygen, I conclude that the principle is not liable to change its state. By the term anthrazothion, I mean anthrazothionic acid deprived of its hydrogen. When this acid comes in contact with easily reducible metallic oxides, its hydrogen combines with the oxygen of the oxide, and forms water, while the anthrazothion forms a combination with the reduced metal.

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I may remark here by the way, that those acids whose radical becomes acid as well by uniting with oxygen as with hydrogen, may be very easily distinguished from each other by the electrochemical properties of the radical. Thus, for example, sulphuric acid might be called schwefelplussäure (sulphur plus acid), and sulphuretted hydrogen schwefelminussäure (sulphur minus acid). By this the cacophony of the frequent repetition of the syllable stoff would be avoided.*

"Sect. 2. Preparation and Properties of Anthrazothionate of Potash.-Porrett has described different methods of forming this salt, which may be seen in his paper. I conceive that it will not be superfluous to give an account of the way by which I procured it in a state of purity.

One part of prussiate of potash in the state of dry crystals was rubbed to a fine powder with the third part of its weight of sulphur, and the mixture beaten down firm into a crucible, in the bottom of which a little sulphur had been previously put. This crucible was put into the fire, covered, raised to a red heat, and allowed to remain at that temperature for half an hour or

* It is obvious that the preceding section relates entirely to the names in the German language. I found some difficulty in making it intelligible to the English, reader, and am not sure that I have succeeded.-T.

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