W. Gibbs—Analytical Notices. 113 
The mean of these analyses is 51°73%, which is precisely the 
percentage required by the formula K,Cr, Cr = 52°2). 
hese analyses show that mercurous nitrate gives very accu- 
rate results. The employment of this salt in separating chrom- 
ium from uranium is indicated only in those cases in which the 
chromium exists as chromic acid, in which relatively small 
quantities of chlorine or sulphuric acid are present, and in 
which no other acid is present which, like phosphoric acid, gives 
an insoluble mercurous salt not completely volatilized by igni- 
tion. In the presence of chlorine, sulphuric acid, &c., the fol- 
lowing process may be very advantageously employed. The 
solution is to be boiled for a few minutes with a small excess 
of sodic hydrate, the precipitate of godic uranate filtered off and 
washed with hot water containing a little sodic hydrate until 
the washings no longer give any turbidity, with a solution of 
mercurous nitrate. ‘The sodic uranate in the filter is then to 
be dissolved in chlorhydric acid, and the uraniuni determined 
in the usual manner. The filtrate contains all the chromium 
as €rO,Na,. After adding chlorhydric acid in excess, the 
chromic acid may be most conveniently reduced to chromic 
oxide by adding a solution of potassic or sodic nitrite and boil- 
ing for a few minutes, after which the oxide may be precipi- 
tated by ammonia in the usual manner. An alkaline nitrite is 
a better reducing agent than alcohol, as the chromic oxide may 
be precipitated immediately after the reduction. 
the precipitate, which has a deep orange color, is to be dis- 
solved in hot nitric acid, the solution boiled for a few minutes 
ignited in the same crucible with the chromic oxide obtained 
as above from the sodic chromate in the filtrate. The filtrate 
is free from uranium. Repeated attempts to determine uran- 
tum by precipitation with sodic phosphate and final weighing 
as uranic pyro-phosphate, have led as yet to no satisfactory 
results. It is, however, worth noting that the Somer phos- 
phate becomes pulverulent, and easily washed by simple evap- 
oration to dryness, 
Am. Jour. ol Fark Sanine, Vou. V, No. 26.-- Fes., 1873. 
