484 SMITH'S INTERMEDIATE CHEMISTRY 



phenol) by nitrating phenol. Picric acid* is a strong acid and forms 

 salts which, with the exception of ammonium picrate, are more 

 sensitive to shock and friction than the acid itself. The action 

 of this explosive on the metals with which it comes in contact 

 must therefore be guarded against. TNT, however, is inert 

 towards metals, and is insensitive towards ordinary shocks. It 

 melts at a low temperature (80), and so can be readily lique- 

 fied and poured into shells. Mixed with ammonium nitrate, it 

 gives amatol (p. 302). 



Toxic Gases. The poisonous substances employed in the 

 Great War were mainly synthetic organic products. Most of 

 these, it is true, were not gases, but liquids or solids of low volatil- 

 ity. Their vaporization was, however, favored by the explosion 

 of the shell in which they were contained, part of the material 

 being converted to gas by the heat of the explosion and the 

 remainder being scattered around in a finely-divided condition. 

 Some of the substances used were so powerful in their action upon 

 the human system that a concentration of 1 part in 10,000,000 

 in the air was sufficient to incapacitate anyone unprotected with a 

 gas-mask. 



The first method employed in gas warfare was to release a 

 highly-volatile poisonous substance (chlorine, or a mixture of 

 chlorine and phosgene COC1 2 ) from cylinders under pressure. A 

 cloud of gas was thus evolved, which under favorable wind condi- 

 tions was carried over the enemy's lines. This cloud method was 

 soon abandoned in favor of the shell method described above. 

 Among the substances thus employed may be mentioned chlor- 

 picrin CC1 3 .NO 2 (made by the action of bleaching powder and 

 lime upon picric acid) and mustard gas (CH 2 C1.CH 2 )2S. The 



* Picric acid is an interesting example of the close interrelation of synthetic 

 organic compounds. It is used in dyeing to give a yellow color, in warfare 

 as an explosive and in medicine as an antiseptic. It may happen that picric 

 acid is used in a base hospital to cure the wound that picric acid caused. 



