hillebband.] WATKK TOTAL OK COMBINED. 45 
central section of the U-shaped absorption tube l<> avoid Large air chan- 
nels. Through this, or any apparatus based on similar principles, the 
air current should always be forced, not drawn. A warm blast directed 
upon the exit tube near its entrance into the absorption tube greatly 
shortens the time required and is to be recommended. 
In this apparatus only the water expelled above 100° to L10 should 
as a rule be determined, and to effect drying of the mixed mineral 
powder and sodium carbonate, after luting the tubulated cap on the 
cylindrical crucible with sodium tungstate, the tube is sunk through a 
round hole in the cover into a small cylindrical air bath (fig. 8), which 
can be heated from beneath by the same ring burner which is subse- 
quently to fuse the flux. A slow current of air is then forced through 
and the drying satisfactorily accomplished. 
The reason why it is unsafe to attempt estimation of u hygroscopic" 
moisture in this apparatus is, that the luting of the two parts must be 
done b} r direct application of a flame to the tungstate, and considerable 
water vapor may enter the apparatus and be in part retained by the 
dried sodium carbonate. 
ChatarcPs apparatus. — The platinum apparatus devised by Dr. Cha- 
tard 1 overcomes the permeability of the metal to gases and affords 
sharp results, moreover permitting of determining by direct absorp- 
tion not only the hygroscopic water, but that which may be driven off 
at any desired temperature, either with or without fluxes. It is, how- 
ever, perhaps even more costly than the Gooch apparatus, and the 
supposed nonliability to injury by warping, because of the protective 
layer of borax and asbestus, can hardly be considered as proved. v 
Merits of the above three forms of apparatus. — All of these appa- 
ratus, except the glass tube of the modified Brush method, permit of 
the estimation of other constituents besides water in the same portion 
if necessary, and by the use of lead chromate or potassium chromate, 
instead of sodium carbonate, graphite, or the carbon of organic matter, 
can be simultaneously determined with the water. 
To one accustomed to its use, and with a drying and suspension 
Attachment permanently set up, the Gooch apparatus, considering its 
limitations above set forth, offers perhaps the most handy and conven- 
ient means for the determination of Avater in rocks. Its high first cost, 
in comparison with the glass tube, is fully made up in time by its 
lu nihility. 
Jannascfts methods. — This zealous deviser of methods for mineral 
maty sis has published in the Zeitschrift fur anorganische Chemie and 
:he Berichte der deutschen chemischen Gesellschaft several papers 
lealing with the problem of water determination in minerals, and in 
lis text-book 2 these are collected in more or less modified form. 
i Am. Chem. Jour., Vol. XIII, p. 110, 1891; Bull. U. S. Geol. Survey No. 78, p. 84, 1891. 
apraktiscner Leitfaden der Gewichtsanalyse. Leipzig, von Veit & Co., 1897. 
