On Cobalt Blue. 
47 
If, for example, in acting on a tenth of the solution, from a 
pound of cinchona, 123 divisions of the alkalimeter are used, 
they represent 1.2 grain, consequently the pound of bark con- 
tains 12 gr. 3 drachms.* 
I believe that this property of tannin may also be made use 
of to ascertain the richness of opium, nux vomica, &c. &c. 
in alkaloids, and also to isolate certain known or unknown 
organic bases in analysis. 
Jour, de Pharm. 
ART. XIV.— ON COBALT BLUE. 
By M. Gaudin. 
Montami, in the preparation of his blue, used a solution of 
arseniate of cobalt in nitric acid, mixed with chloride of so- 
dium. He evaporated this solution almost to dryness, but 
not carried so far as to drive off all the acid ; he obtained in 
this way a blue, which he exposed to the air, where it at- 
tracted moisture, became red, and soluble in water. In a few 
days he subjected the moist mass to the action of heat, to ex- 
pel the excess of acid, again exposed it to the air, and re- 
peated these processes, till the substance was no longer sus- 
ceptible of becoming red, or of tinging water of a rose co- 
lour. In this preparation, the arsenic acid attacked the oxide 
of sodium, as it gradually became separated from the nitro- 
muriatic acid ; and the oxide of cobalt thus set free was 
transformed into cobaltic acid and combined with the soda - r 
to enable it to become fully developed, the substance must be 
heated to redness after having washed it. The same result 
is obtained if the black oxide of cobalt be combined with the 
* As each division of the graduated measure, represents but a very small 
portion of quinine, no great error can arise if two or three divisions more are 
filled ; for 0,0037 gr. multiplied by 3 = quinine 0,0219 gr. or in the pound, 
multiplied by 10 = quinine 0,219 gr. 
