PIERRE EUGENE MARCELLIN BERTHELOT 111 



followed in 1870 by investigations on the explosive force 

 of powders, the explosions being carried out in a calori- 

 meter. 



In 1871 Berthelot proceeded to investigate the detona- 

 tion of mixtures of gases, and he made measurements of 

 the heat of formation of nitro-glycerine. In 1874 and 

 1876 the work was continued ; and in 1877 it was extended 

 to the temperatures of explosive mixtures, and to the 

 velocity of combustion. In 1878 explosive mixtures of 

 dust with air, and in 1880 fulminating mercury, were 

 examined. A research on the velocity of the explosive 

 wave in gases followed in 1882 ; and in 1884 measure- 

 ments of the specific heats of gases at high temperatures 

 were made. In the same year the calorimetric bomb was 

 invented ; and in 1892 it was adapted to the requirements 

 of organic analysis. 



Allotropic varieties of the elements also claimed Ber- 

 thelot's attention. In 1857 he commenced with a study 

 of allotropic varieties of sulphur ; and in 1870 he investi- 

 gated these varieties thermally. In 1869 he examined 

 the allotropic varieties of carbon, and this led him to the 

 preparation of various forms of graphitic oxides. Allo- 

 tropic silver and other allotropic forms were also the 

 subject of his research. 



Berthelot also did much work by help of the 'silent 

 discharge.' Attracted to it in 1876, when he submitted 

 mixtures of organic substances with nitrogen to its 

 influence, and succeeded in causing the nitrogen to enter 

 into combination, he repeated Brodie's experiments, and 

 reproduced the oxide C 4 4 . In 1878 he produced by the 

 same means the higher oxide of sulphur, S 2 7 , in needles 

 often a centimetre in length, and in 1881 pernitric 

 anhydride. In 1895 he carried out similar work with 

 argon, and later with helium. 



From an early date Berthelot interested himself in 



