“224 Analysis of the Substance 
His memoir is printed among the proceedings of the 
Royal Academy of Sciences for the year 1715. We may 
therefore consult his observations for every thing that re- 
Jates to the position of the mines and the extraction of the 
turquoises. 
As to the experiments made by M. Reaumur with the 
view of depriving them of their colour, although not alto- 
gether conclusive, yet it will be useful to ‘mention them 
here, as they are connected with the means I resorted to in 
order to ascertain the nature of the turquoise. I shall there- 
fore present my readers with that part of M. Reaumur’s 
memoir. 
<¢ The colouring matter,”’ he says, ‘ which fills the cel- 
hues of the turquoise, and which tinges the whole stone, is 
certainly a distinct substance. But is it a simple mineral 
substance like cobalt, or the substance of which azure and 
sapphire are formed, and which give such a fine blue colour 
to china and earthen-ware; or is it a metallic substance ?”’ 
This is a question which I have not been able to resolve to 
my own satisfaction. 
<< I supposed at first that our turquoises derived their co- 
lour from copper, this metal yielding a blue and a green co- 
lour; but I saw that we might discharge the colour from 
them as we do from coral: of all the solvents I tried, di- 
stilled vinegar succeeded best with me. If a thickish piece 
of turquoise is steeped for an hour or two in this vinegar, its 
corners become white; and in two or three days all the sur- - 
face of the stone, and even almost all its interior, assumes 
the same colour. 
<< The vinegar, besides taking away the colour, also dis- 
solves the stone, which is always covered with a kind of 
white cream composed of the particles which had been de- 
tached from it. Citron juice also dissolves these kind of 
stones, but it only weakens their colour; and that part 
which is below the sort of cream above mentioned is blue 
when the stone has been steeped in this juice. 
“¢ As to aqua-fortis and aqua-regia they are not proper for 
extracting the colour from our turquoises: they dissolve 
very speedily the whole substance of the stone; but they 
supply 
