264 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



ment of mixing them, expecting that common air might be 

 produced. Instead, he obtained a crystalline deposit of 

 sal-ammoniac. This salt is, therefore, a compound of the 

 two gases with one another. In 1809, Gay-Lussac showed 

 (A.C.R. IV. 10) that sal-ammoniac is formed by the union 

 of ammonia and of hydrogen chloride in equal volumes. 



Both gases, although regarded as simple substances when 

 they were first prepared, were afterwards shown to be com- 

 pounds containing hydrogen. Sal-ammoniac is, therefore, 

 a ternary compound of nitrogen, hydrogen and chlorine : ' 



[AMMONIA = {NITROGEN 



SAL-AMMONIAC = -[ J HYDROGEN 



[MURIATIC ACID GAS = {CHLORINE 



It is analogous with the oxygen-salts such as : 



SULPHATE F/ COPPER OXIDE 



COPPER = j SULPHURIC ANHYDRIDE = 



but differs from them in being formed by the union of two 

 hydrides instead of two oxides. Such salts were described 

 as hydrogen- or HYDRO-SALTS, in contrast with the better- 

 known oxygen- or OXY-SALTS (see, for instance, Turner's 

 "Chemistry," 1847, I. 566). 



Davy (1807) suspects the presence of oxygen in 

 ammonia. Davy's success in isolating metals from the fixed 

 alkalis (see below, pp. 273-280) led him, in 1807, to 

 suspect that the volatile alkali might also contain a metallic 

 constituent in combination with oxygen and hydrogen. 



"As the two fixed alkalies contain a small quantity of 

 oxygen united to peculiar bases, may not the volatile alkali 

 likewise contain it? was a query which soon occurred to 

 me in the course of inquiry ; and in perusing the accounts 

 of the various experiments made on the subject, some of 

 which I had carefully repeated, I saw no reason to consider 

 the circumstance as impossible" (Davy's Works, V. 92). 



