H. Wurtz on the Indigo Test. 55 
-to in a former paper. Some — details, however, of a spe-_ 
a character are necessary 
The chlorids of cobalt and nine are used reciprocally, after 
the manner of Dr. Gibbs, to neutralize the colors of each other. 
- The color of the mixture, as I have obtained it, is when concen- 
trated rather graytsh than brownish as it is designated by Dr. 
Gibbs.* This slight residual color is however of no conse- 
guenes as all that is necessary is to get rid of all admixture of 
dlue tint, before adding the indigo solution. In working with 
cobalt solutions it must be carefully borne in mind that the or- 
~ 2 eha 
he green colors of solutions of copper, chromium, and ura- 
nium are neutralines 3 in the same manner as solutions of nickel, 
water it is combined with, sae? in dilute solutions Bie but on 
admixture with strong muria uriatic acid or on heating, assuming a 
tint. Now it is only the green chlorid which 
neutralizes the chlorid of cobalt, so that it is necessary to have 
sufficient muriatic acid present to ensure the existence of the 
copper salt in the green modification, at least while the liquid i 
hot. The color produced is then very similar to that 
with the chlorids of cobalt and nickel. In the onion aleae 
lution of chlorohydrate of uranic acid, the green tint is perfectly 
obliterated by chlorid of cobalt, a light salmon tinge being pro- 
duced which does not interfere with the in sess ) 
SO ME ae 
of chlorid of chromium is precisely similar in its action to one | ere 
of chlorid of nickel, the resultant color with  ahtorid of « 
: ny identical in appearance. A concentrated green solution of 
The chlorid of cobalt used was chemically pure, having been prepared by the 
ine (am or, Sr [2 i 200) whch os are 
the dissolving the residual 
id and sesquioxyd of ¢ ate muriatic acid an ling 
+ Lieb. and Kopp’s Jahresb. 1855, 414. 
ecole of ts pra! evaporation, a Giles tae  exiresly i 
color. The chlorid of el used was also prepared with care, and was of high | 
