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tin, by their yielding a fparkling red precipitate with 
volatile fpirits, &c. A far more minute proportion 
of platina, mixed Avith gold, is more dihinguifhable 
by thefe procehes, than by thofe with alkaline falts 
above-mentioned ; thefe exhibiting the whole of the 
platina diflolved by itfelf, thofe only a part of it. 
4. By metallic Solutions . 
All the metals, which precipitate gold from aqua- 
regia, have been already (hewn to precipitate platina 
alfo. As gold is thrown down by fome metallic fo- 
lutions, as well as by the metals in fubhance, par- 
ticularly thofe of mercury and iron, it remains to 
apply thefe liquors as precipitants for platina. 
1. A faturated folution of mercury in aqua-fortis, 
which readily and totally threw down gold in its me- 
tallic form, being added to a folution of platina, the 
liquor became immediately turbid, and, on handing 
for a little time, nearly the whole of the platina fell 
to the bottom. A folution of mercury in the ma- 
rine acid, or of corrofive fublimate, likewife preci- 
pitated platina, but lefs perfectly, and with this dif- 
ference, that the former precipitate was of a greyilh 
brown colour, the latter of a fparkbng red. 
2. Solutions of iron in the vitriolic acid, or of 
common green vitriol in water, which totally threw 
down gold, happily made no change in folutions of 
platina. Compofitions of platina and gold being dif- 
folved in aqua-regis, the folutions diluted with about 
twice their quantity of water, and a filtered folution 
of the vitriol gradually added ; the mixtures inhantly 
grew turbid, and,, on handing, depofited the gold in 
form 
