§§ 773> 774 -] arsenic. 603 
warm-blooded animals, and found at various periods arsenic, not alone 
in the intestinal canal, but also in the spleen, liver, and kidneys. 
§ 773. Analysis of Wall-Paper for Arsenic. —The separation of 
arsenic from paper admits of great variety of manipulation. A quick 
special method is as follows :—The paper is saturated with chlorate of 
potash solution, dried, set on fire in a suitable plate, and instantly 
covered with a bell-glass. The ash is collected, pulverised, and ex¬ 
hausted with cold water, which has previously thoroughly cleansed the 
plate and bell-glass ; the arsenic in combination with the potash is dis¬ 
solved, whilst oxides of chromium, copper, aluminium, tin, and lead 
remain in the insoluble portion. 1 
Fresenius and Hintz 2 have elaborated a method for the examination 
of wall-papers, fabrics, yarns, and similar substances, which, provided 
the reagents are pure, is accurate and easy. Twenty-five grms. of the 
substance are placed in a half-litre distilling flask or retort, and 250 c.c. 
of HC1, specific gravity 1-19, added ; after digestion for an hour, 5 c.c. 
of a saturated solution of ferrous chloride are added, and the liquid 
slowly distilled until frothing stops any further distillation. A further 
quantity of 100 c.c. HC1 is then added, and distilled over. The re¬ 
ceiver, in each case, contains water, and must be kept cool. The united 
distillates are diluted to 800 c.c. and saturated with SH 2 . The arsenious 
sulphide is collected on an asbestos filter. After partial washing, it is 
heated with bromine in HC1 of 1*19 specific gravity, and the solution 
again distilled with ferrous chloride. The distillate, on now being 
treated with SH 2 , gives arsenious sulphide free from organic matter. 
§ 774. Estimation of Arsenic. —Most of the methods for the quanti¬ 
tative determination of arsenic are also excellent tests for its presence. 
It may be regarded, indeed, as an axiom in legal chemistry, that the 
precise amount of every substance detected, if it can be weighed or 
estimated by any process whatever, should be accurately stated. In¬ 
definite expressions, such as, “ a small quantity was found,” “ traces were 
detected,” etc., are most objectionable. The more perfect of the methods 
of evolving arsine are now quantitative, because the arsenical ring can 
be compared with standard rings produced under as nearly as possible 
the same experimental conditions. Pure arsine, passed into nitrate 
of silver solution, decomposes it in such a manner that, if either the 
silver deposited or the free acid is estimated, the quantity of arsenic 
can from such data be deduced. A very convenient method, applicable 
in many cases, is to throw out the silver by hydrochloric acid, alkalise 
the filtrate by bicarbonate of soda, and titrate with iodine solution. 
The latter is made by dissolving exactly 12-7 grms. of pure dry iodine 
by the aid of 19 grms. of potassic iodide in one litre of water, observing 
1 Kapferschlaeger, Rev. Universelle des Mines , 1876. 
2 Zeit. anal. Chem., xxvii. 179-182. 
