^{page 288 note *} Nicholson's Journal, vol. xxxi. p. 126.

^{page 290 note *} Nicholson's Journal, vol. xxxii. p. 186, &c.; vol. xxxiv. p. 271.

^{page 292 note *} Nicholson's Journal, vol. xxxi. p. 129.

^{page 292 note †} Id. vol. xxxiv. p. 274.

^{page 294 note *} A foreign chemist, who has continued to support the old doctrine of the nature of muriatic acid, has observed, (Annals of Philosophy, vol. viii. p. 204.) that the water of the muriatic acid gas cannot be supposed to be obtained by the combination of the acid with ammonia, for no neutral ammoniacal salt, he adds, can be obtained free from water, and the water of the acid gas becomes the water essential to the salt. I did not think it necessary to make any reply to this observation, founded entirely, as it appeared to me, on a mistaken assumption. But I may take this opportunity of remarking, that there is no necessary truth in the supposition that the ammoniacal salts must contain water which they cannot yield. When acids combine with bases, the water of the acid does not necessarily remain in the compound. On the contrary, it is capable of being driven off from the greater number of them, by an elevated temperature; and there is no principle on which it cari be inferred, that ammonia should in this respect be different from other bases. That it is incapable, as the same chemist remarks, (Annals, vol. vii. p. 434.) of combining with a dry acid, so as to form a neutral compound, is of no weight; for the same thing is true of other bases, which yet, when combined with such an acid by the aid of water, allow this water to escape from the combination. He himself observes, that well-burnt lime, free from water, does not absorb dry carbonic acid gas, but absorbs it rapidly if aqueous vapour be admitted, though water is not retained in the composition of carbonate of lime. And I have found, that dry magnesia does not absorb muriatic acid gas, though with the aid of water it forms a combination from which the water can be expelled by heat. That ammoniacal salts exist without water, is evident from the combination of carbonic acid gas and ammoniacal gas, being effected with the greatest facility; and the circumstance that this compound is not neutral, is one not depending on the peculiarity of the ammonia, and its not containing water, like other bases, but on that of the carbonic acid, which, with all the alkalis, even where water is present, has a tendency to form compounds with excess of base. The reason why the ammoniacal salts do not yield the combined water of their acids so completely as that of other salts, is, that from their volatility, or their susceptibility of decomposition, they do not bear that degree of heat which is necessary to produce it. I cannot, therefore, but consider the observation alluded to, as one altogether unfounded, and which ought not on mere speculation to have been brought forward against a positive result.

^{page 300 note *} The action of the metals on the muriatic acid gas, taking place in the above experiments at a heat comparatively moderate, it occurred to me, that they might exert a similar action with no higher heat on the acid, in muriate of ammonia, and that this might afford an easy mode of exhibiting the results. I accordingly found, that on mixing different metals with sal ammoniac in powder, previously exposed to a subliming heat, and exposing the mixture to heat by a lamp, so regulated as to be short of volatilization, the salt was decomposed, ammoniacal gas was expelled, and moisture condensed in the neck of the retort; covering a space of several inches with small globules, and at length running down. The metals I employed were iron, zinc, tin, and lead; 100, 150, or 200 grains of each metal, dry and warm, being mixed with 100 grains of the salt, likewise newly heated. To obviate any fallacy from common sal ammoniac being employed, I repeated the experiment with the salt formed from the combination of its two constituent gases, and obtained the same result. But although this affords an easy mode of exhibiting the production of water, it is not favourable to obtaining a perfect result, the heated ammoniacal gas carrying off a considerable portion of the water deposited; and accordingly, the quantity, instead of increasing as the experiment proceeds, at length diminishes, and the ammoniacal gas deposites a portion of water in passing through mercury, or in being conveyed through a cold tube.

^{page 304 note *} Recherches Physico-chimiques, t. ii. p. 133.

^{page 315 note *} It is curious with regard to the most important of these analogies, that of the equivalent or combining weights, that oxymuriatic acid stands next to sulphurous acid; the former in Dr Wollaston's scale being 44, while the latter will be found to be 40. The acidity of oxymuriatic acid is fully established by the most unequivocal acid property, that of combining with alkalis, and forming neutral compounds. The saline nature of these compounds had been shewn by Berthollet; that with lime has been demonstrated by Mr Dalton, who also pointed out the probability from the results, by double decomposition, that the acid combines in a similar manner with other salifiable bases; and the existence of these compounds has been established by Mr Wilson.

^{page 318 note *} The difficulty of entirely excluding water and hydrogen from the constituents of this gas is sufficiently apparent. And the fact, that it cannot be formed from them by the action of the electric spark, but only by the continued action of solar light, is favourable to the above opinion. The conversion of carbonic oxide into carbonic acid, by the joint action of oxymuriatic gas and hydrogen, an experiment which I performed when the new hypothesis with regard to the nature of chlorine was brought forward, and which was attempted to be invalidated by some singular controversial methods, I consider as depending probably on the same principle.