HILLEBRAND.] TITANIUM. 7l 
cover is removed at the top next the glass end to permit of the inser 
tion of the glasses side by side in such a way that no light shall pene- 
trate around their sides or between them. Immediately hack of the 
glasses is a partition P, with openings of appropriate size cut in it. 
A stiffly sliding black cardboard shutter S is movable up and down 
immediately back of the partition, so that all light can be cut oil except 
that which comes through the liquid. 
Precautions of this kind are necessary if accurate results are to be 
counted on. Except for mere traces, this combination of glasses and 
darkened box insures greater accuracy and rapidity of work than Ness- 
ler tubes, and is preferable likewise, so far as the writer's experience 
goes, to expensive instruments like the colorimeter of Soleil-Duboscq, 
etc. In making the color comparisons the box is best held close to a 
window, so as to get a full, strong light. Daylight is far preferable to 
artificial light. 
gooch's gkavimetric method. 
When titanium is present in excess of 4 to 5 per cent and whenever 
for any reason it is desired to employ a gravimetric method, among 
the few that have been thoroughly tested that of Dr. Gooch 1 is 
uncqualed. With one or two minor modifications introduced by Dr. 
T. M. Chatard, 2 it is as follows: 
Any solution of the rock freed from silica can be used, and the first 
step is to remove the iron. This is best done, after adding tartaric 
acid and reducing the iron by means of hydrogen sulphide to the fer- 
rous condition, by rendering the solution ammoniacal and introducing 
more hydrogen sulphide. If the iron is not thus reduced before pre- 
cipitation, titanium will be in part thrown down also. 3 The amount of 
tartaric acid is to be gauged according to the combined weights of the 
oxides to be held by it in solution, and three times this weight is ample. 
After removing the iron sulphide by filtration — little washing suffices, 
because of the relatively small amount of titanium commonly pres- 
ent — the tartaric acid is destroyed as follows: 
Potassium permanganate to the extent of two and one-half times the 
weight of the tartaric acid used is made into a strong solution, and to 
the ammoniacal filtrate from the iron sulphide enough sulphuric acid 
is introduced to leave some excess after all the permanganate has been 
reduced. After expulsion of hydrogen sulphide by boiling the per- 
manganate is added gradually to the hot solution contained in a large 
beaker or flask. A vigorous reaction ensues. When a permanent 
brown precipitate of manganic hydrate appears the tartaric acid has 
iProc. Am. Acad. Arts Sci., n.s., Vol. XII, p. 435; Bull. U. S. Geol. Survey, No. 27, p. 16, 1886; Chemical 
News, Vol. LII, pp. 55 and 68, 1885. 
2 Am. Chem. Jour., Vol. XIII, p. 106, 1891; Bull. U. S. Geol. Survey, No. 78, p. ^7; Chemical New-. Vol. 
LXIII, p. 267, 1891. 
3Cathrein: Zeitschr., fur Kryst., Vol. VI. p. 213, 1882; Vol. VII, p. 250, 1883. 
