256 CHEMISTRY. 



time Lave been slaves to the habit are in good health even 

 at the age of sixty years or more. 



360. Arsenetted Hydrogen. Arsenic, like nitrogen and 

 phosphorus, combines with hydrogen in the proportion of 

 one atom to three. This body, arsenetted hydrogen, AsH 3 , 

 or hydrogen arsenide, as it is sometimes called, is a gas, 

 neither acid nor alkaline, and very poisonous. A German 

 chemist, named Gehlen, was fatally poisoned by it in 1815, 

 while investigating its properties. It is easily obtained 

 by throwing a little arsenious anhydride into an apparatus 



for generating hy- 

 drogen by means 

 of zinc and sul- 

 phuric acid. The 

 arsenious oxide 

 is deprived of its 

 oxygen, and part 

 of the metal com- 

 bines with the hy- 

 drogen, forming ar- 

 senetted hydrogen. 

 This gas is inflam- 



Fi s- 97 - mable, and burns 



with a lambent flame ; if a cold porcelain plate be held in 

 the flame a moment, the gas being decomposed by the 

 combustion, metallic arsenic will be deposited on the por- 

 celain, forming gray-black spots. This formation of ar- 

 senetted hydrogen and of a metallic deposit by the flame 

 is made use of in testing for arsenic. The delicacy of the 

 test is remarkable : -^^-QQ of a gramme can be detected in 

 this manner, using suitable precautions not necessary to 

 describe here. Antimony forms a similar compound with 

 hydrogen, SbH 3 , and the flame of this gas deposits a black 

 metallic coating on a cold porcelain surface just like ar- 



