266 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



rapidly in volume, the quicksilver loses its fluidity, and at 

 length becomes of the consistency of soft butter, and 

 arborescent crystallisations shoot from it, which are quite 

 solid. The amalgam so formed has perfectly metallic 

 properties. It effervesces copiously when thrown into water, 

 hydrogen gas is given off, and a solution of ammonia is 

 found in the water. When exposed to the air it gradually 

 loses its consistence ; it emits a strong odour of ammonia, 

 and reddens paper tinged with turmeric held above it ; and 

 at last is found merely quicksilver. 



" I found a still more easy mode of making the amalgam 

 by employing mercury combined with a minute quantity of 

 potassium, sodium or barium. 1 When a compound of this 

 kind is placed in contact with a solution of ammonia, or 

 any moistened ammoniacal salt, it enlarges to eight or ten 

 times its bulk, and becomes a soft solid, and may be pre- 

 served for a much longer time than the amalgam formed by 

 electrical powers ; it changes very slowly even under water " 

 (Works, IV. 353-354; the quotation is from Davy's 

 "Elements of Chemical Philosophy," published in 1812). 



Composition of the amalgam from ammonia. Davy 

 thought at first that the amalgam might have been formed 

 by deoxidation of ammonia and "attempted to procure a 

 peculiar metallic substance from it by distillation out of the 

 contact of air, but without success ; . . . on the application of 

 heat, hydrogen and ammonia were always evolved, and the 

 mercury recovered its former state. ... In the most 

 accurate experiments the proportions of ammonia and 

 hydrogen were two to one by volume " ( Works, IV, 355). 



As these products were formed, even from carefully-dried 

 amalgam, he was obliged to adopt the alternative view of 

 Gay-Lussac and Thenard that " the amalgam consists of 

 mercury united to azote and hydrogen, the hydrogen being 

 in larger proportion than in ammonia" (Works, IV. 354). 

 Since two volumes of ammonia contained one volume of 

 nitrogen and three volumes of hydrogen, the compound 

 1 See below, pp. 275, 278, 281. 



