What he actually obtained was mainly a mixture of the so-called phospham and chlorophosphamide, remarkably stable substances, the characteristic properties of which he describes with accuracy. He then examined the action of ammonia gas on sulphur chloride, “the sulphuretted muriatic liquor of Dr. Thomson,” but as the compounds formed
“did not present the same uniform and interesting properties as that from the phosphoric sublimate, I did not examine them minutely: I contented myself by ascertaining that no substance known to contain oxygen could be procured from oxymuriatic acid in this mode of operation.”
He then shows that ammonia and oxymuriatic acid, in condensing to sal ammoniac with liberation of nitrogen, contrary to the general belief, form no water. According to Cruickshank, who appears to have been the first to make the observation, “hydrogenous gas” required rather more than its own volume of oxygenated muriatic acid to saturate it when a mixture of the two was exploded by means of the electric spark, “the products being water and muriatic acid.” Gay Lussac and Thenard had stated that no water was thus formed.
“I have attempted,” says Davy, “to make the experiment still more refined by drying the oxymuriatic acid and the hydrogen by introducing them into vessels containing muriate of lime [calcium chloride] and by suffering them to combine at common temperatures; but I have never been able to avoid a slight condensation; though in proportion as the gases were free from oxygen or water, this condensation diminished.[I]
“MM. Gay Lussac and Thenard have proved by a copious collection of instances, that in the usual cases where oxygen is procured from oxymuriatic acid, water is always present, and muriatic acid gas is formed; now as it is shewn that oxymuriatic acid gas is converted into muriatic acid gas by combining with hydrogen, it is scarcely possible to avoid the conclusion, that the oxygen is derived from the decomposition of the water, and consequently that the idea of the existence of water in muriatic acid gas, is hypothetical, depending upon an assumption which has not yet been proved—the existence of oxygen in oxymuriatic acid gas.
“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.