244 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP 



Gay-Lussac (1815) prepares and analyses anhydrous 

 prussic acid. Gay-Lussac, in 1811, (Ann. de Chimie, 1811, 

 77, 128) prepared anhydrous prussic acid by distilling its 

 mercury salt with concentrated hydrochloric acid. In his 

 memoir" On Prussic Acid" (Ann. de Chimie, 1815, 95, 

 136-231), he describes it as follows : 



" It is a colourless, odorous liquid, with a taste at first 

 fresh, then burning . . . and a true poison. Its density 

 at 7 is 07058; at 18, 0*6969: it boils at 26*5, and 

 solidifies about 15 below the temperature of melting ice; 

 it then crystallises regularly and sometimes assumes the 

 fibrous form of nitrate of ammonia. The cold which it 

 produces in vaporising, even in air at 20, is sufficient to 

 freeze it. This phenomenon is easily produced by putting 

 a drop at the end of a slip of paper or a tube of glass. 

 Although I rectified the acid several times over powdered 

 marble, it always kept the property of reddening blue litmus 

 paper slightly : the red colour disappeared as the acid 

 evaporated" (Ann. de Chimie, 1815, 95, 145-146). 



The anhydrous acid was vaporised into oxygen and 

 exploded in a Volta's eudiometer. It gave an equal volume 

 of carbonic anhydride and half its volume of nitrogen ; one 

 and a quarter volumes of oxygen were used, of which one 

 volume was required to produce one volume of carbonic 

 anhydride, whilst the one-quarter volume was used in burn- 

 ing one-half a volume of hydrogen. 



Gay-Lussac concluded that the acid "contained one 

 volume of carbon-vapour, one-half volume of azote and 

 one-half volume of hydrogen," but no oxygen. The correct- 

 ness of this analysis was proved (i) by the density of the 

 gas, (2) by passing it over iron heated in a porcelain tube, 

 when carbon was deposited and a gaseous mixture of equal 

 volumes of hydrogen and nitrogen was set free (Ann. de 

 Chimie, 1815, 95, 147-152). 



Gay-Lussac regards prussic acid as a hydracid. After 

 completing his analyses, Gay-Lussac writes : 



