METALLIC OXIDES. 
123 
white precipitate, as well as the carbonate ; but this precipitate Oxides of tin* 
is easily dissolved in a large portion of caustic alkali ; and it 
does not become the least grey, even the moment before its 
dissolution. 
The white stanneous oxide, precipitated by the carbonate of 
kali, dissolved easily, and without disengaging carbonic acid 
in the acids, and even in the nitric. It is, therefore, not a 
carbonate. When heated in a small retort, which was half 
full, it yielded pure water, and left a greyish powder, which 
was black at the bottom. I filled the retort a second time 
entirely with the white oxidp, and heated it anew. I obtained 
water, but the oxide which remained was quite black. On 
being taken out of the retort, and triturated into a fine powder, 
it had a colour composed of green, brown, and grey. Heated 
at the point of the flame of a candle, the oxide took fire, and 
continued to burn like amadou, or tinder fungus, leaving a 
white greyish powder. It follows from this, that the stanneous 
oxide is black, and that the white powder precipitated by the 
alkali was only a hydrate of the oxide. This hydrate is 
exactly the same as the oxide itself, very combustible, and, 
when lighted at the point of flame, it continues to burn of 
itself, though with less brightness than the pure oxide. If the 
hydrate be carefully washed and mixed with water, and the water 
heated to ebullition, the hydrate is decomposed, and the black 
stanneous oxide remains by itself. The phial in which I made 
this experiment was, by accident, laid aside in a place where it 
remained four months $ and the black oxide was, at the expi- 
ration of this time, very little altered ; for it had only a slight 
layer of the white oxide on the surface. 
These experiments prove, that there is nothing in the cha- 
racters of the stanneous oxide, which justifies the conclusion, 
that the black film produced on melted tin, is a sub-oxide, and, 
consequently, the existence of this sub-oxide, is yet very pro- 
blematical. 
In order to determine the composition with regard to quan- 
tity of the stanneous oxide, it not being possible to be done in 
a direct manner, I employed the following method : 
I melted together, in a glass retort, pure tin and sulphur, and 
obtained a greyish mass, which was porous, and had a metallic 
lustre 3 I then reduced it to powder, and mixed it with half of 
its 
