146 Method df analysing Stones. 



powder : throw this mixture, by little and little, into A 

 red-hot crucible, and repeat the operation three times^ adding 

 each time to the residue new quantities of potash and of 

 charcoal. 



The mass resulting from these detonations ought after- 

 wards to be mixed witli one part of black, flux, and exposed* 

 during an hour, in a crucible, to a red heat. Leave the 

 whole to cool, separate the metallic cobalt and pulverize it, 

 and bring the mixture to detonate with tlwi same precautions 

 indicated above. 



The iron contained in the cobalt oxidates itself very 

 stronglv, and the aciditicd arsenic combines with the pot- 

 ash. Wash several times the pulverized mass, and by ti- 

 tration separate the arseniate of potash, which has been 

 formed, from the insoluble residue which contains the co- 

 balt. 



Treat this residue with nitric acid, which dissolves the 

 cobalt without attacking the iron, which is carried to its 

 maximum of oxidation. 



Evaporate the solution to dryness ; redissolve the residue 

 in the nitric acid, and filter the liquor to separate the last 

 portions of oxide of iron which might have escaped at the 

 first operation. 



ft only remains, then, to decompose the nitrate of cobalt 

 by potash, to wash the precipitate, and to operd;tc the 

 reduction of it by means of heat. 



XXXIII. On a Method of analysmg Stones containing fixed 

 Alkali, by Means of the. Boracic ykid. .% Humphry 

 Daw, Esq. F.R. S., Professor of ChemistryAn the Royal 

 Institution* . 



A HAVE found the bcM^cic acid a very useful substance for 

 bringing the constituent parts of stones- containing a fixed 

 alkali into solution. 



Its attraction for the different simple earths is considerable 

 at the heat of ignition, but the compounds that it forn-»s 

 with them are easily decomposed by the mineral acids dis- 

 solved in water, and it is on this circumstance that the 

 method of analysis is founded, 

 • The processes are very simple. 



• From the Transactions uf tht- Royal .'^orifty for 1805. 



100 grains 



