162 oT, H, LABY. 
tion of the nickel and cobalt as sulphides. The electro- 
lytic determination, which is highly accurate and con- 
venient, cannot be readily combined’ with the acetate 
process as some experimenters find that ammonium chloride 
is detrimental to the deposition of the nickel and cobalt. 
Test Analyses. 
In the following experiments, Table I., the amount of 
iron mentioned was taken in the form of a solution of the 
nitrate together with cobalt or nickel nitrates and evapor- 
ated in a porcelain dish on a water bath to dryness. It 
was found that the iron is precipitated as ferric hydrate 
most readily when the evaporation is stopped just before 
dryness, and the formation of a very basic nitrate of iron 
is avoided. The residue from the evaporation was diluted, 
brought to the boil and the lead monoxide added while the 
solution was boiling either in the dish or preferably ina 
conical flask. On the addition of sufficient lead oxide (six 
times the weight of the iron present) ferric hydrate sepa- 
rated out in a form which was readily filtered; but often 
the washing was most tedious, and some of the precipitate 
passed through the filter paper. In the first experiments 
hot water was used, but it was found better as would be 
expected, to wash with a solution of some salt, lead nitrate 
being the one used. The presence of a small quantity of 
ferric hydrate does not interfere with the accuracy of the 
electrolytic deposition of nickel and cobalt. The filtrate 
contains the nitrates of lead and cobalt or nickel. This 
lead was removed in some cases by evaporating the filtrate 
nearly to dryness, adding an excess of sulphuric acid, 50 cc. 
of 5 HK. to every 1—2 grams of lead present, decomposing 
the nitrates, diluting, and finally filtering off the lead sul- 
phate. In the case of experiments 5, 6, 8 and 9, Table I., 
1 Electrolytic Methods of Analysis—Neumann; but compare Oettel,: 
Zeitschr. f. Electro chem. 1894,1 , 194. 
