a mineral Substance from North America, 55 
deep blue, with a tinge of purple, but, when held between the 
eye and the light, it appears of a greenish gray colour, 
C. 
It is perfectly insoluble, and remains unchanged in colour, 
and in every other respect, when digested in boiling concen- 
trated nitric acid. 
D. 
It is dissolved by boiling sulphuric acid, and forms a tran- 
sparent colourless solution, which is however only permanent 
while the acid remains in a concentrated state ; for, if a large 
quantity of water be added to the solution, or if the latter be 
poured into a vessel of distilled water, the whole in a few 
minutes assumes a milky appearance, and a white precipitate is 
gradually deposited, which cracks as it becomes dry upon the 
filter, and, from white, changes to a lavender-blue colour, and 
again, when completely dry, to a brownish gray. It is then 
insoluble in water, has not any flavour, is semi-transparent, and 
breaks with a glossy vitreous fracture. 
This substance is much heavier than the original white pre- 
cipitate ; and in a very slight degree may be dissolved by boiling 
muriatic acid, or by boiling lixivium of potash. 
Upon examining these solutions, I found that both contained 
the original white substance, together with some sulphuric acid; 
so that the precipitate obtained from the sulphuric solution by 
the addition of water, is a sulphate of the white matter.* 
The whole is not however precipitated by water ; for a part 
* This sulphate is also precipitated when the sulphuric solution has been long ex- 
posed in an open vessel to the air ; and, according as this may be moist or dry, the 
effect is produced sooner or later. 
