46 
SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
For the majority of silicates he finds dehydrated borax powder a 
most efficacious flux, usually at a very moderate temperature. The 
fusion is accomplished either in a platinum boat within a glass tube 
or in a tube of the form and dimensions shown in the accompairying 
fig. 10. 
For rocks or minerals containing not much fluorine a retaining layer 
of granular lead chromate, or of previously fused and powdered lead 
oxide, is used as shown at a. Plugs of glass wool are used at <?, c. 
Whether or not the boat is employed the borax is first introduced 
Fig. 10. — Glass tube for determination of water (Jannasch). b, mixture of mineral powder with 
borax; c, c, plugs of glass wool; a, layer of lead chromate or lead oxide. Total length of the tube, 
33 cm.; inside diameter, 12-14 mm. 
and, together with the retainer, is thoroughly dried out in an asbestos 
oven by a hot-air current. Then, after cooling, the mineral powder 
is added and thoroughly mixed with the borax. Heat is applied by a 
flat flame to the mixture, which soon melts and forms a clear fusion, 
when the action is complete. The blast may be used in extreme cases. 
The layer of retainer must be kept warm by an auxiliary flame, and 
the absorption tube must be removed before the flame under the fused 
mass is extinguished, for the glass breaks as soon as this is done. 
Carbon dioxide can simultaneously be determined by attaching a soda- 
•^CE 
I£I_JI1 
Fig. 11.— Glass tube for determination of water in special cases (Jannasch). Length from a to e, 
26 cm.; inside diameter somewhat over 1 cm.; volume of bulb b, 25 cm 3 , c d, retaining layer of lead 
oxide between plugs of glass wool; /, calcium chloride absorption tube; g, protective tube. 
lime tube to the calcium-chloride tube. For one-half to 1 gram of 
silicate Jannasch uses li to 2 grams of borax. 
Regarding the borax method, its inventor insists upon the following 
points as essential to success, especially when the blast can not be 
applied: Most thorough mixing of flux and mineral powder and a 
most impalpable fineness of the latter. 
The borax itself is prepared by heating pure ciystallized borax in a 
platinum dish till a small portion has melted. That remaining unf used 
is powdered and again heated in the dish to dull redness for fifteen 
minutes, with constant stirring. The powder is placed in a tube with 
