708 foisons : their effects and detection. [§§ 906 , 907 . 
production of Rinman’s green. The supposed sulphide is dissolved off 
the filter with hot nitric acid, a drop or more (according to the quantity 
of the original precipitate) of solution of cobalt nitrate added, the solution 
precipitated with carbonate of soda and boiled (to expel all carbonic 
anhydride) ; the precipitate is then collected on a filter, washed, dried, 
and ignited in a platinum dish. If zinc be present in so small a pro¬ 
portion as 1 in 100,000, the mass will be permanently green. 
Minute quantities of zinc, as, for example, may occur in drinking- 
water, may be separated by the method of Bertrand and Javillier. 1 
500 c.c. of the aqueous liquid is mixed with 50 c.c. of lime water, excess 
of ammonia added, then filtered ; the filtrate is boiled until the ammonia 
is expelled. A precipitate forms of highly refractive crystalline hydrated 
calcium zinc oxide, Ca(—0—Zn0H) 2 4H 2 0 ; the crystals are minute, and 
under the conditions mixed with lime carbonate. The crystals may be 
collected on a small filter, dissolved in dilute HC1, the lime separated 
by NH 3 and oxalate of ammonia; the filtrate from the lime oxalate 
is evaporated to dryness, gently ignited, first adding a little sulphuric 
acid so as to convert into zinc sulphate, a soluble salt easily identified. 
§ 906. Other methods of procedure are as follows :—The supposed 
zinc sulphide (after being well washed) is collected in a porcelain dish, 
and dissolved in a few drops of sulphuric acid, filtered, nitric acid added, 
evaporated to dryness, and heated to destroy all organic matter. When 
cool, the mass is treated with water acidulated by sulphuric acid, and 
again filtered. The solution may contain iron as well as zinc, and if the 
former (on testing a drop with ferrocyanide of potash) appears in any 
quantity, it must be separated by the addition of ammonia in excess to 
the ammoniacal fdtrate ; sodic carbonate is added in excess, the liquid 
well boiled, and the precipitate collected on a filter and washed. The 
carbonate of zinc thus obtained is converted into zinc oxide by ignition, 
and weighed. If oxide of zinc, it will be yellow when hot, white when 
cold ; it will dissolve in acetic acid, give a white precipitate with sul¬ 
phuretted hydrogen, and, finally, if heated on charcoal in the oxidising 
flame, and moistened with cobalt nitrate solution, a green colour will 
result. Zinc may also be separated from liquids by electrolysis. The 
best results are obtained from alkaline solutions and a strong current 
at a temperature of 50°. 
2. NICKEL—COBALT. 
§ 907. The salts of nickel and cobalt have at present no toxicological 
importance, although, from the experiments of Anderson Stuart, 2 both 
1 Compt. Bend. 1 , 1906, p. 900. By suitable concentration of a liquid, zinc can in 
this way, be separated if less than T V grain per gallon. 
2 “ Nickel and Cobalt : their Physiological Action on the Animal Organism,” by 
T. P. Anderson Stuart, M.D., Journ. of Anat. and Physiol., vol. xvii., Oct. 1882. 
