72 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
been fully broken up, and the precipitated manganese is to be redis- 
solved by a few drops of ammonium bisulphite or of sulphurous acid 
solution. 
Ammonia is then added in slight excess, followed at once by acetic 
acid in considerable excess, and the boiling is continued for a few 
minutes. Thereby the titanium is freed from most of the alumina, and 
from lime and magnesia if they had not. been earlier removed, also 
from most of the manganese introduced. The precipitate is filtered 
and washed with water containing acetic and sulphurous acids, then 
ignited, fused thoroughly with sodium carbonate, and leached with 
water to remove phosphoric acid and most of the remaining alumina. 
The residue is again ignited and fused with sodium carbonate. To 
the cooled melt in the crucible strong sulpuric acid is to be added, 
wherein it dissolves readily by aid of gentle heat. This solution is to 
be poured into a small volume of cold water and the platinum it con- 
tains precipitated by hydrogen sulphide at or near boiling temperature. 
After filtering and cooling, ammonia is added till the titanium is just 
precipitated, and a measured volume, containing a known weight of 
absolute sulphuric acid, is then added — just enough to redissolve the 
precipitate. The solution is then made up with acetic acid in such 
amount that the final bulk shall contain from 7 to 11 per cent of 
absolute acid, and then enough solid sodium acetate is stirred in to 
more than take up the sulphuric acid introduced. Upon rapidly 
bringing the liquid to ebullition the titanium is precipitated in 
flocculent and easily filterable condition, and the precipitation is com- 
plete after a minute's boiling, provided all the prescribed conditions 
have been followed and zirconium is absent. 
The precipitate is washed first with acetic acid of 7 per cent strength 
and then with hot water. After 15 to 20 minutes' ignition over a good 
burner it is in condition for weighing and will lose no more weight 
over the blast lamp. For large amounts of titanium a repetition of 
the sodium carbonate fusion, etc., should be made. The actual carry- 
ing out of all these operations, when once the method is understood, 
requires much less time than the detailed description would indicate. 
gooch's method not directly applicable to rocks containing zirconium. 
Prior to the adoption of the colorimetric method, Dr. Gooch's was 
invariably used in this laboratory. Occasional inability to secure clean 
and complete precipitation by it was experienced, especially with a 
certain series of rocks rather poor in titanium. Long research showed 
the difficulty to be due to the presence of zirconium, which acts as a 
marked preventive of the precipitation of titanium by boiling in an 
acetic acid solution under the conditions of the Gooch method. 
The above rocks were found to contain up to 0.2 per cent of Zr0 2 , 
and this amount was able to prevent precipitation of 0.3 per cent of 
