42 
SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
upturned flange of the crucible proper. Both rings and burner can be 
clamped firmly at any height. 
The rock powder, having been placed in the cylindrical crucible 
(C, fig. 7), is there mixed with not more than 3 or 4 grams of fully 
dehydrated sodium carbonate, 1 or more of lead chromate if carbon is 
to be likewise determined. The crucible is sunk in its seat S (fig. 8) in 
the upper ring R' and the tubulated cap T (fig. 7) is fitted on and attached 
to the calcium chloride drying towers — preceded by one containing 
potassium hydroxide if carbon dioxide is likewise to be estimated — on 
Fig. 7, 
-Modified form of the Gooch tubulated platinum crucible for the determination of water 
one-half natural size. Weight about 88 grams. 
the one side, and to a sulphuric-acid bulb tube B (fig. 9) on the other. 
Powdered sodium tungstate — free from arsenic, which would soor 
ruin the crucible lips — is now poured into the flanged lip L (fig. 7) ir 
which the cap rests, and a metal vessel of cold water having beer 
raised up by the lower ring R" (figs. 8 and 9) until the platinum crucible 
is sufficiently immersed, the flame of an ordinary blast lamp is turnec 
on to melt the tungfstate. As soon as this is fused the flame is removec 
1 This has been heated for a length of time to near its fusing point over a free flame or in an ai 
bath, to decompose the bicarbonate it usually contains, and then placed in a desiccator. Thusheatc 
it is not very hygroscopic. Penfield found that 2.5 grams of it, spread out on a watch glass, gaine' 
only .0002 gram in 15 minutes. Potassium carbonate and potassium-sodium carbonate are too hygrc 
scopie by far to be available. 
