the AttraSllve Powers of Mineral Acids. 1 7 
vitriolic air and fulphur. 100 grs. of iron, diflolved without 
heat, afford upwards of 400 of vitriol. 
100 grs. of the vitriol cryftallized contain 25 of iron, 20 of 
real acid, and 55 of water. When calcined nearly to rediiels 
thefe cryftals lofe about 40 of water. 
The calces of iron are more or lefs foluble in this acid 
according to their degree of dephlogiftication. Thofe that are 
phlogifticated (as that recently precipitated from a folution ot 
vitriol by fixed alkalies) are all'o moll; foluble, and upon eva- 
poration afford cryftals, though paler than thofe formed of ge- 
nuine iron. Thofe that are leaf! phlogifticated are alfo leaft 
foluble, that is, require more real acid for their folution, and 
afford no cryftals, but only a magma or mother liquor. Hence 
a-lfo, folutions of iron newly made diminilh, and confequently 
phlogifticate the fuper-incumbent air, and confequently gra- 
dually emit phlogifton : and hence the calx, being more de- 
phlogifticated, gradually falls unlefs more acid be added to keep 
it in folution. 
Iron in the nitrous acid . 
100 grs. of iron, to be perfectly diflolved, and not barely 
calcined, require 142 grs. of real nitrous acid, fo diluted as 
that its proportion to water ftiould be as 1 to 1 3 or 1 4 ; and 
when this laft proportion is ufed, the heat of a candle may be 
applied for a few feconds, and the accefs of common air pre- 
vented. In this cafe not above 18 cubic inches of nitrous 
air are produced, all the reft is abforbed by the folution, 
and no red vapours appear. But if the proportion of ; acid 
and water be as 1 to 8 or 10, and heat be applied, a much 
greater quantity of iron will be dephlogifticated, though 
very little of it be held in folution ; and by this means 
I have obtained from 100 grs. : of iron, 83,87 cubic inches 
Vox. LXXIII. D * of 
