TURQ.UOIS STONE. | 85 



His memoir is printed among those of the Royal Academy of Reference to 

 Sciences, for the year 1715, which may be consulted for every *rquoTses,"&e. 

 thing which bears relation to the situation of the mines, and the 

 extraction of the turquoises. 



With regard to the experiments made by the author, in or- 

 der to discolour these substances, though not very conclusive, 

 it appears to me, nevertheless useful, to bring together these 

 facts along with the means which I have employed to ascertain 

 the nature of the stone. I shall first present a few fragments 

 of this part of Reaumur's memoir. 



The colouring matter, says theau!hor, which fills the cellules Rea^u^^^^.g ^^^ 

 of the turquois, and which afterwards tinges the whole stone, servations on 

 is, no doubt, a particular substance; but is It a simple mineral 'l^e colouring 

 matter, like cobalt, or (he material from which azure and sap- 

 phor are made, from which the finest blue of porcelain, and 

 pottery is served ; or, is it a metallic matter ? I have not been 

 able to satisfy myself in this respect. 



I at first suspected that our turquoises might probably derive 

 their colour from copper. This metal is capable of affording a 



blue, and a green But I have found that the turquoises it^r^j taken up 



may be extracted like that of coral ; of all the solvents, which I by vinegar. 

 have used, distilled vinegar succeeded the best. If a thin 

 piece of turquois be steeped in this vinegar, its angles, after 

 an hour or two, become white ; and in two or three days, the 

 whole of the upper surface of the stone, and even its internal 

 parts, assume the same colour. 



Vinegar, while it extracts the colour, likewise dissolves the 

 stone ; it is always covered with a kind of white cream, com- 

 posed of parts ,which have been detached. Juice of lemons 

 likewise dissolves this kind of stone, but it only weakens the 

 colour; and that which is found under the kind of cream, we 

 have described, is blue, when the stone has been put into this 

 liquid. 



As to aquafortis, and aquaregia, they are not proper to ex- . f - • &r 

 tract the colour from our turquoises ; they very speedily dissolve applied to 

 the whole substance of the stone, but they afford the means of these stones, 

 distinguishing the Persian turquoises from those of France. 

 Aquafortis does not act upon those of Persia ; whence it fol- 

 lows, that these two kinds of stone, though similar in ap- 

 pearance, are nevertheless of a very different nature ; it would 

 fee wrong, however, to draw a consequence to the disadvan- 

 tage 



