270 EXAMINATION FOE ARSENIC 



si urn), the nitre, and the hydrate of potassa (for the 

 third case), which must first be converted into sul- 

 phate by adding sulphuric acid. The quantities em- 

 ployed for testing should not be too small ; at least 

 an ounce of each reagent should be taken. 



When the reagents have been tested in this manner, 

 and shown to be absolutely free from arsenic, the 

 examination of the substance may be proceeded with. 

 The solution to be tested, containing any arsenic which 

 may have existed in the body, is poured through the 

 funnel tube b into the apparatus filled with hydrogen, 

 and from which hydrogen is being evolved, the tube e 

 being already heated to redness at the same spot. In 

 order that none of the liquid may remain in the tube 

 b, the latter is rinsed with about the same quantity of 

 pure water, care being taken that no air is poured in 

 with it. 



If arsenic be present, there will soon appear, in the 

 portion of the tube e, beyond the heated spot, a dark 

 stain, which is at first brownish, and afterwards becomes 

 lustrous and gradually increases until, when large 

 quantities of arsenic are present, it forms an opaque 

 metallic mirror. At the same time the gas issuing 

 from the tube e may be kindled, and a dish of white 

 genuine porcelain held in the flame, which should not 

 be too feeble; lustrous black or brownish spots of 

 metallic arsenic will then be deposited, and a great 

 many may sometimes be obtained. When the heated 

 portion of the tube is not very long, more or less 

 arsenetted hydrogen escapes decomposition and fur- 

 nishes the above-mentioned spots. No imitation of 

 porcelain (stone-ware or delf) should be employed for 

 this purpose, since the glaze of these materials very 

 often contains lead, the reduction of which might pro- 

 duce dark spots even though no arsenic were present. 

 If a large quantity of arsenic be contained in the mix- 

 ture, so that many thick arsenic-spots can be obtained, 



