hillebrani..] ALUMINUM, TOTAL IRON. 57 
remaining residue in hot, strong sulphuric acid and diluting with cold 
water. 1 
ESTIMATION OF IRON IN TIIK PKECTPITATE OF ALUMINA, ETC. 
Without regard to the presence of vcmadium. — The nitrate obtained 
in the preceding paragraph is reduced, hot, by hydrogen sulphide, 
boiled to collect sulphur and the platinum sulphide ' ; resulting from the 
bisulphate fusion, the hydrogen sulphide being allowed to pass for a 
short time after boiling. It is then filtered 8 hot into a flask attached 
to a carbonic-acid apparatus and brought to boiling to expel hydrogen 
sulphide. When this is fully effected the flask is cooled in water 
while the carbon dioxide still passes, and the solution is then titrated 
by potassium permanganate. The results are strictly accurate, with 
the limitations set forth in the paragraph below, when care is taken 
with the reduction by hydrogen sulphide. The method is altogether 
superior to that involving the use of zinc, since no foreign impurity 
affecting the result is introduced and the ever-present titanium is 
not affected, nor is vanadium reduced below the condition of V 2 4 , 
whereas nascent hydrogen converts it, in part at least, to V 2 3 . 
Titanium can be conveniently estimated by adding hydrogen peroxide 
to the titrated iron solution (see p. 68). 
-Some years ago, in a series of analyses of rocks from the Leucite Hills, in Wyoming, there was 
obtained at this stage, when it was customary to dissolve the melt in cold water preliminary to pre- 
cipitation of titanium by boiling the neutralized sulphuric solution in presence of sulphur dioxide, ;i 
white, more or less flocculent residue amounting to 1 to 3 per cent of the rock, which was at first 
taken to be a mixture of tantalicand columbic acids. Eventually it was found to consist apparently 
of nothing but Ti0 2 and P 2 0r„ with perhaps a little ZrOo. By repeated fusion with acid potassium 
sulphate and leaching with cold water it could be gradually brought into solution. It was these rocks 
which furnished the most striking instance of the peculiar, milky, sulphate residues mentioned on 
p. 53, as derived from the ignited silica. 
Knop (Zeitschr. fur Kryst., Vol. X, p. 73,1885) seems to have obtained a similar mixture in analyz- 
ing minerals from the Kaiserstuhl in Baden, but its nature was not ascertained, though suspected t" 
be, if not silica, columbiferous titanic acid. 
2 It may be mentioned that the precipitation of platinum from a hot sulphate solution is far quicker 
and cleaner than from hydrochloric acid. Further, this platinum sulphide, when Ignited in the 
crucible in which the bisulphate fusion was made, should weigh together with the crucible itself 
what the latter weighed before the main silica precipitate was ignited in it; in other words, the weight 
of the platinum recovered by hydrogen sulphide should equal the loss in weigh! of the crucible due 
to attack by the bisulphate. Insomewhal rare instances tins will not hi' so, but the weighl will he 
greater, showing a gain in platinum winch may amount to a milligram. Tests have shown that this 
is not due to retention of platinum by the main Al 2 3l etc., precipitate; hence, it musl come from 
platinum mechanically loosened from the dish during the drying and powdering of the silica pre 
paratory to its collection on the filter, or to some insoluble compound of platinum formed during 
evaporation and drying of the silica. It may also he in part or wholly due to contamination from 
reduction of platinum during evaporation of the filtrate from the basic acetate separation. It will 
be remembered that from this filtrate a small amount of iron and alumina isrecovered and added 
to the main precipitate. Eenceil isalwayswell in line work to colled thesulphide and weigh the 
platinum in the original crucible, deducting any excess from the alumina, or else to gel rid of the 
platinum by hydrogen sulphide before proceeding to the precipitation of alumina, etc. i see p 54 |. 
3 Filtration is not necessary if only precipitated sulphur and no sulphides are in suspension, since 
this is without reducing action on cold permanganate solution as Wells and Mitchell, and others 
before them, have pointed out. The above authors used this method of reducing ferric iron in titanic 
iron ores. i. lour. Am. chem. Sue., Vol. XVII, p. 78, L895; also Chemical News. Vol. LXXIII, p. L23, 
18%.) 
