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Nitre upon Gold and Platina. 
Having found that nitre would dissolve gold, I tried whether 
it would produce any effect upon platina. 
It has been formerly observed that the grains of platina, in 
the impure state in which it is originally found, might, by be- 
ing long heated in a crucible with nitre, be reduced to powder. 
Lewis, from his own experiments and those of Margraaf, 
thought that the iron only which is contained in the grains of 
platina was corroded by the nitre. But by heating nitre with 
some thin pieces of pure platina in a cup of the same metal, I 
found that the platina was easily dissolved, the cup being much 
corroded, and the thin pieces entirely destroyed. By dissolving 
the saline matter in water, the greater part of the platina was 
precipitated in the form of a brown powder. This powder, 
which was entirely soluble in marine acid, consisted of the 
calx of platina, combined with a portion of alkali, which could 
not be separated by being boiled in water. The platina which 
was retained by the alkaline solution communicated to it a 
brown-yellow colour. By adding an acid to it a precipitate 
was formed, which consisted of the calx of platina, of alkali, 
and of the acid which was employed. 
Silver, I found to be a little corroded by nitre. But as its 
action upon that metal was very inconsiderable, it did not ap- 
pear to be deserving of a more particular examination. 
alkali of the nitre does not assist in producing this effect. Nitrous acid alone, which 
does not contain its full proportion of oxygen, occasions the same precipitation, unless 
it is very strong ; and if a mixture of such strong nitrous acid, and of a solution of 
gold in nitrous acid, is dropped into water, the gold is deprived of its oxygen, and is 
precipitated of a blue colour. Two causes contribute to produce this effect upon the 
addition of vyater. The adhesion of the calx of gold to nitrous acid is by that means 
weakened, and the oxygen is attracted more strongly to the imperfect nitrous acid, in 
consequence of their attraction for water when they are united. 
