CHEMICAL PRINCIPLES. 
U57 
purple colour given to animal and vegetable treated with the mu- Oudes ofjold* 
riate of gold, is owing to this degree of oxidation. Tiie third 
circumstance (being the presence of a large quantity of water) 
tends to weaken the affinity of the muriatic acid. I'he purple 
varies in the intensity of its colour according as the liquid is 
more or less diluted j and with its colour its composition also 
varies. Not, however, that there exists more than one pro- 
portion constituting the true combination ; but that, when 
the quantity of water is too small, the precipitate contains a 
considerable portion of the black metallic alloy, and when 
the quantity is too great, a quantity of the white oxide of tin 
is precipitated with the purple, and gives a greater brightness 
and transparency to its colour. This will immediately appear 
on pouring some of the muriate of tin into a large quantity of 
water, when the oxide of tin will be gradually deposited in the 
form of a vidiite voluminous, semi-transparent powder. 
As to the problem, how is the purpleformed P its most pro- 
bable solution seems to be the following. The murias stannuaus, 
diluted with a quantity of water sufficient to diminish the affinity 
of the muriatic acid to the higher degrees of oxidation of the 
tin, reduces the murias auricus to the state of an inter- 
mediate oxide of a purple colour (oxidum aureum.) A por- 
tion of the oxidum stanneum, formed by this reduction of the 
oxide of gold, combines with the oxidum aureum ; and, as the 
acid can no longer hold them in combination, they are pre- 
cipitated, whilst another portion of the oxidum stanneum re- 
mains in the solution, in form of a supermuriate. If this 
explanation be the true one, it follows, that the real composi- 
tion of the purple must take place in such manner as that if 
the oxigen in the oxidum aureum be = 1, that of the oxidum 
stanneum will be = 6, and that of the water «= 3. 
I very much regret, that I have not been able to contrive any 
experiment whereby this point might be put beyond doubt, and 
the existence or the non-existence of an intermediate oxide 
clearly established. 
FT. 
