Ordinary Meeting, January 25 th, 1.870, 
E. W, Binney, F,RS., F.G.S., Vice-President, in the Chair. 
“ Stannic Arsenate,” by William Carleton Williams, 
F. C.S., Demonstrator in the Chemical Laboratory of the 
Owens College. 
A mixture of moderately concentrated aqueous solutions 
of stannic chloride and arsenic acid gradually thickens on 
standing, and after the lapse of two or three weeks solidi- 
fies, forming a transparent colourless noncrystalline mass. 
In order to ascertain the composition of this substance I 
subjected a considerable quantity of it to dialysis; hydro- 
chloric acid and the excess of arsenic acid or stannic chloride 
passed through the dialyser, leaving a gelatinous residue of 
pure stannic arsenate. This jelly is heavier than water, it 
floats in a liquid having a specific gravity P135. Strong 
acids, and solutions of caustic potash or soda, dissolve it 
readily. In water it dissolves very slowly. From this 
aqueous solution certain reagents reprecipitate the arsenate 
of tin as a gelatinous mass, identical in its appearance, proper- 
ties, and composition with the original jelly. These reagents 
are hydrochloric, nitric, and sulphuric acids, the chlorides of 
barium, calcium, ammonium, and iron, also silver nitrate 
and potassium iodide. Alcohol, acetic acid, sodium phos- 
phate, mercuric chloride, and the carbonates of sodium, 
potassium, and ammonium, do not produce any change. 
This substance contains a large amount of water, the 
greater part of which is expelled at a temperature of 100° C. 
A small quantity however is retained most pertinaciously, 
and is not driven off at 200°, Below a dull red heat decom- 
position takes place and fumes of arsenious oxide escape. 
51*9 grm. dried at 100° C. left 1*9 grim, residue. Loss of 
water = 50 grm. or 9 6 ’3 per cent. 
The residue somewhat resembles gum arabic in appear- 
Proceedings— Lit. & Phil. Soc.— Vol. XV.— No. 6.— Session 1875-6. 
