Estimation of Nickel in Pyrrhotites and Mattes. 179 
separating the iron by ammonium hydrate, even with all the 
precautions recommended by various authors, has given very 
unsatisfactory results in our hands, By far the best success 
was obtained in the use of the method given by Frederick 
Field, in the Chemical News, vol. i, page 5 (1859). The method 
is as follows: 
“In the case of nickel and iron, the nitrates are evaporated 
nearly to dryness, and, after the addition of water, oxide of lea 
(litharge) is added, and the whole boiled for ten minutes or a 
quarter of an hour. The iron is entirely precipitated, the ni- 
trates of nickel and lead remaining in solution. After filtration, 
which can be effected with great readiness, dilute sulphuric 
acid is added, and on standing for sixteen hours the sulpha‘e 
of lead is filtered off, and the nickel precipitated and estimated 
in the usual manner.” 
This process uniformly gave good results as to the separation 
of iron and nickel, all the nickel being left in solution. The 
containing acetic acid. The filtrate is heated nearly to boiling 
and caustic potash added until the odor of ammonia is distinctly 
