268 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



sulphuretted hydrogen as a sulphide . . . ; finally with a 

 volume of hydrochloric or hydriodic gas, as a chloride or 

 iodide of this compound metal" ("On a Natural Classifica- 

 tion of Simple Substances," Ann, Chim. Phys., 1816, 2, 

 1 6, footnote). 



According to Ampere's view the composition of sal- 

 ammoniac should be represented as follows : 



SAL- 



AMMONIAC = - 



AMMONIA 



NITROGEN I 



HYDROGEN 



MURIAT.CGAS CHLORINE = CHLQRINE 



This view was supported by the analogy of cyanogen (p. 245), 

 a poisonous gas containing nitrogen and carbon, which 

 "although a compound substance, shows all the properties 

 of the simple substances [chlorine, iodine, sulphur, etc.] 

 capable of acidifying hydrogen." 



Berzelius, convinced at last that ammonia contained no 

 oxygen, adopted Ampere's view, and in 1823 {Jahresbcrickt, 

 1823, 2, 57) proposed to represent the composite metal 

 ammonium by a symbol Am, analogous with those which he 

 had already proposed for the metallic elements (p. 295). 



Absorption and liberation of water in salt-formation, 

 For many years confusion prevailed in reference to the 

 composition of salts, because no attention was paid to the 

 appearance or disappearance of water ; this water cost nothing, 

 and, even when not in use as a solvent, could only be 

 excluded by very careful drying. 



It was recognised that salts can be formed by the direct 

 combination of two oxides, two sulphides or two hydrides, e.g. 



Two oxides : litharge + ^dride ~^ lead sul P hate v 

 Two hydrides \ ammonia + muriatic gas > sal-ammoniac. 



