“MM. Gay Lussac and Thenard indeed have stated an experiment, which they consider as proving that muriatic acid gas contains one-quarter of its weight of combined water. They passed this gas over litharge, and obtained so much water; but it is obvious, that in this case, they formed the same compound as that produced by the action of oxymuriatic acid on lead; and in this process the muriatic acid must lose its hydrogen and the lead its oxygen; which of course would form water; these able chemists, indeed, from the conclusion of their memoir, seem aware, that such an explanation may be given, for they say, that the oxymuriatic acid _may_ be considered as a simple body.” [I] Theoretically, there should be no contraction. One volume of chlorine combines with one volume of hydrogen to form two volumes of hydrogen chloride [muriatic acid gas]. Dalton’s law of gaseous volumes had been established by Gay Lussac before 1810. He then repeats the experiments which first led him to suspect the existence of combined water in muriatic acid. “When mercury is made to act upon 1 volume of muriatic acid gas, by voltaic electricity, all the acid disappears, calomel is formed, and about ·5 of hydrogen evolved.” The same result is obtained by the use of potassium. “And in some experiments made very carefully by my brother, Mr. John Davy, on the decomposition of muriatic acid gas, by heated tin and zinc, hydrogen, equal to about half its volume, was disengaged, and metallic muriates, the same as those produced by the combustion of tin and zinc in oxymuriatic gas, resulted.” “It is evident from this series of observations, that Scheele’s view (though obscured by terms derived from a vague and unfounded general theory) of the nature of the oxymuriatic and muriatic acids, may be considered as an expression of facts; whilst the view adopted by the French school of chemistry, and which, till it is minutely examined, appears so beautiful and satisfactory rests in the present state of our knowledge upon hypothetical grounds.” He then proceeds to explain the action of water upon the chlorides of tin, and phosphorus; and shows that it is by the decomposition of the water that the hydrogen is furnished to the oxymuriatic acid, and the oxygen to the tin and phosphorus. “The vivid combustion of bodies in oxymuriatic acid gas, at first view, appears a reason why oxygen should be admitted in it; but heat and light are merely results of the intense agency of combination. Sulphur and metals, alkaline earths and acids become ignited during their mutual agency; and such an effect might be expected in an operation so rapid as that of oxymuriatic acid upon metals and inflammable bodies.”