70 On the Oxides of Gold, Tin, &c, 



cipitate. All these changes will take place more rapidly 

 if, before performing the precipitation and re-solution by 

 the liquor of caustic potash, the muriatic solution of tin is 

 diluted with six or eight parts of water. In this case there 

 uill be no perceptible extrication of caloric, and there will 

 be no precipitation of tin in a metallic state. This solution, 

 the oxidation of which approaches to the term of minimum, 

 preserves in general, without any precipitation of oxide, an 

 aqueous transparency. Exposed for a long time to the at- 

 mospheric air, it does not lose the property of changing the 

 yellow oxide of gold into gray, and of extracting the blackish 

 brown colour of the oxide of manganese fixed upon a piece 

 of cotton. 



The oxide of manganese may present itself under different 

 degrees of oxidation. If we impregnate a piece of cotton 

 cloth with a transparent solution of sulphate of manganese, 

 it will preserve its whiteness in drying ; upon plunging the 

 piece of cotton cloth thus impregnated into a solution of 

 potash in a state of carbonate or of causticity, it will, when 

 washed, be changed into a brown colour by the action of the 

 atmospheric air. This colour will acquire a very dark hue, 

 almost approaching to black, upon being allowed to remain 

 some time in an alkaline oxymuriatic solution. This oxy- 

 genated alkaline liquor will assume a purple colour, of a more 

 or less transparent intensity, on leaving therein exposed, a 

 longer or shorter time, some brown precipitate of manganese 

 in place of a piece of cloth coloured with this metallic sub- 

 stance, which therein dissolves itself, being oxidated by the 

 fluid. 



In general, it is proper to attend to particular results in 

 exposing all the metallic oxides to the action of this oxyge- 

 nated niiiriatic alkaline liquor. This, perhaps, would be the 

 means of giving them acid properties, and of proving at the 

 same tin)e more and more' the gradual oxidation of most 

 metals. Above all, it may be remarked of the white oxide 

 of lead, which becomes gradually more and more coloured 

 by a long exposure in this oxygenated liquor, in which it i« 

 necessary, nevertheless, to stir it often. 



The muriatic and nltro-muriatic solutions of tin, 'very 



much 



