A solution of commercial tin chloride is prepared by pouring on 1 part of the salt 6 of boiling distilled water, and the solution is filtered through a cloth into a cylindrical glass vessel, in order to allow the foreign substances which are sometimes found in the chloride to deposit. The filtration by means of filtering-paper is too slow, and it is always attended with the loss of a subchloride which does not pass through filtering-paper; therefore this filtration is not practicable, and may be completely replaced by passing the solution through linen. Into the still hot and almost clear solution of tin chloride is poured a concentrated solution of oxalic acid; a white precipitate of oxalate of protoxide of tin is formed. After complete cooling, the liquor is decanted, and the precipitate is washed on a cloth with cold water until the washing water has no longer an acid reaction. The tin oxalate is afterwards heated, dried on an iron plate, or in a boiler of the same metal, over a small charcoal fire. The decomposition of the salt commences at red heat, and there remains, after the disengagement of carbonic acid gas, and carbonic oxide, a quantity of tin oxide in the state of extreme division.

During the decomposition, which must be accelerated by stirring with an iron wire, the matter undergoes a considerable increase of bulk, consequently it is necessary to employ for this operation very spacious vessels, so as to avoid loss. (Watt.)