ARSEXIC. 



189 



be sublimed from the copper by placing it in a narrow test-tube 

 and heating. 



9. Fleitmanris test. Zinc and solution of sodium h}-drate 

 evolve, upon heating, hydrogen gas: 



Zn + 2NaHO = Na 2 Zn0 2 -f 2H. 



If arsenious or arsenic acid be present, arseniuretted hydrogen 

 is evolved, which may be recognized by placing over the mouth 

 of the flask in which the reaction takes place a 

 piece of paper, moistened by a drop of silver 

 nitrate solution, which latter is decomposed by 

 the arseniuretted hydrogen with liberation of free 

 silver, which imparts to the paper a purplish- 

 black color. (Antimony compounds do not 

 evolve antimoniuretted hydrogen, when treated 

 with zinc and alkaline hydrates.) (Fig. 8.) 



10. Marsh's test. This test is, especially for 

 the detection of traces of arsenic, by far the best 

 and most reliable, and should never be omitted in 

 testing for arsenic in cases of poisoning. The 

 apparatus used for performing this test consists of 

 a glass vessel (flask or Woulf s bottle) provided 

 with a funnel-tube and a delivery r tube (bent at 

 right angles), which is connected with a wider 

 tube, tilled with pieces of calcium chloride or 

 plugs of asbestos ; this drying tube is again con- 

 nected with a piece of hard glass tube, about one 

 foot long, having a diameter of | inch, drawn 

 out at intervals of about 3 inches, so as to reduce 

 its diameter to | inch. Hydrogen is generated 



in the flask by the action of sulphuric acid on zinc, and exam- 

 ined for its purity by heating the glass tube to redness at one 

 of its wide parts for at least 30 minutes ; if no trace of a metallic 

 mirror is formed at the constriction beyond the heated point, 

 the gas and the substances used for its generation may be pro- 

 nounced to be free from arsenic. (Both zinc and sulphuric 

 acid sometimes contain arsenic.) 



After having thus demonstrated the purity of the hydrogen, 

 the suspected liquid, which must contain the arsenic either as 



