METALLIC OXIDES. 
131 
with alkalis, earths, and metallic oxides, are soluble in acids. Oxides of tin. 
whilst the combinations of the oxide at a maximum, always 
leave the hydrate of the oxide undissolved. 
The hydrate of the ojjnde at a maximum, is easily dissolved 
in caustic alkali. The solution produces crystals by evaporation, 
which are white, and in the form of grains, and have a 
caustic and alkaline taste, but as it was not possible to purify 
them from the very concentrated lixivium in which they were 
deposited, I have not been able to analyse them. If, on the 
contrary, the alkali be diluted with water, and as much oxide 
of tin added to it as the alkali will dissolve, a fluid is obtained 
which is of a dusky yellow colour, and when looked at through 
the light, becomes opal and whitish. This liquor does not 
afford crystals, but on evaporation forms a jelly which dries 
slowly, and then becomes a yellowish mass, which is soluble 
again in water. At a red heat this combination is decomposed, 
the oxide becomes insoluble, and the alkali remains and may be 
separated from it by water. If, on the contrary, this mass is 
burned with an excess of alkali, it becomes white, and the 
oxide is rendered soluble in acids. This experiment proves, 
that the affinity of the oxide of tin is so weak, that heat de- 
prives it of the power of remaining in combination, and re- 
duces it to a state of insolubility, notwithstanding the affinity 
of the bodies with which it is actually combined. The effect 
of an excess of alkali in the fire seems, in part, to be analo- 
gous to what we see in silex, alumine, &c. and in part depends 
on the circumstance, that the oxide is reduced to an inter- 
mediate degree of oxidation. 
(To be continued.) 
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