ARSENIC. 
§ 768.] 
591 
just above its melting-point sodium is mixed with it in the proportion of 
about 1 grain to each pound of zinc. The crucible is then heated until 
the zinc is completely fluid, and the zinc is poured into a second heated 
crucible and back again into the first crucible to ensure thorough 
melting. The crucible, with the lid on, is then put back into the 
furnace and heated to a dull-red heat, when the furnace and crucible 
lids are both removed, and the heating is continued for one hour. A 
scum rises to the top and forms a crust on the surface. This crust, 
when the crucible has cooled a little, is pierced at one side and the molten 
mass is poured into a second heated crucible and skimmed if necessary. 
The crucible is then heated to bright redness, any scum removed, then 
allowed to cool and the zinc granulated just before the solidifying 
point is reached. Arsenic-free zinc prepared in this manner, and much 
of the commercial arsenic-free zinc, is often “ insensitive,” i.e. it retains 
a certain amount of arsenic, so that qualititive results may be too low 
or traces overlooked. 
M. Blondlot, 1 several years ago, made the observation that if 
stannous chloride be added to the contents of the flask in the Marsh- 
Berzelius process, the whole of the arsenic is given off even in the 
presence of pure zinc and acid, and Chapman and Law 2 have recently 
found that 1 to 2 grms. of cadmium sulphate, lead acetate, or 
stannous chloride completely overcome the “ insensitiveness ” of the 
pure materials. The same authors have shown that such salts as 
palladium chloride, platinum chloride, nickel sulphate, and cobalt 
sulphate cause, on the other hand, a retention of large quantities of 
arsenic; working also with alloys of zinc with iron, nickel, cobalt, 
copper, silver, platinum, sodium, tin, and cadmium, they found that all 
of these, with the exception of tin and cadmium, caused retention of 
arsenic, but in every case the insensitiveness ” was removed by the 
addition of 2 grms. of cadmium sulphate, lead acetate, or stannous 
chloride, except in the case of some metal alloys. 
Hydrochloric Acid .—Various methods have been proposed for freeing 
hydrochloric acid from traces of arsenic. Of these we will only give 
two of the most recent and convenient. 
Ling and Rendle’s Method . 3 —This is based upon the fact, observed 
by H. Cantoni and J. Chautenis, 4 that methyl arsenite is readily formed 
and is very volatile, and that the Reinsch method as modified by Dr 
L. T. Thorne 5 may be used for the purification of hydrochloric acid. 
1 Blondlot, “ Transformation de l’arsenic en hydrure solide par l’hydrogene faissant 
sous l’influence des composes nitreux,” Jour, de Pharm. et de Chim., 3 e ser., xliv. 486. 
2 A. C. Chapman and H. D. Law, “ The Reducing Action of Hydrogen,” Analyst, 
Jan. 1906, p. 3. 
3 Arthur R. Ling and T. Rendle, “ Note on the Removal of Arsenic from Hydro¬ 
chloric Acid for use in the Marsh-Berzelius Method,” Analyst, Feb. 1906, p. 37. 
4 Arch. Sc. Phys. Nat. Geneve (4), xix. 364. 5 Proc. Chem. Soc., 1902, p. 118. 
