hillebrand.] WATER — TOTAL OR COMBINED. 89 
vents loss of water by circulating air currents. The tube being hold 
horizontally, the bulb is heated to any required degree by the Bunsen 
or blast flame. Moistened filter paper or cloth wound about the cooler 
parts of the tube insures condensation of all water. The heated end 
being finally pulled off, the tube is weighed after cooling and external 
cleansing, and again after the water has been removed by aspiration. 
For most rocks, as they contain little water, central enlargements of 
the tube are hardly needed. 
Various forms of tubes used by Penfield are shown in fig. 4. 
Before using, even if apparently dry, "these tubes must be thor- 
oughly dried inside, which is best accomplished by heating and aspirat ing 
a current of air through them by means of a glass tube reaching to the 
bottom." 
How this simple tube is made to afford entirely satisfactory results 
3 
Fig. 4.— Penfield's tubes for water determination in minerals, a, b, c, different forms of tubes; 
d, thistle tube for introducing the powder; e, capillary-tipped stopper. 
with minerals, even when carbonates are present, is fully set forth in 
the paper cited. 
Few rocks, comparatively, arc altogether free from other volatile 
constituents. Hence, for refined work the application of this appa- 
ratus in the simple manner above set forth is limited. It may, how- 
ever, be used with the addition of a retainer for fluorine, sulphur, etc., 
in the shape of calcium, lead, or bismuth oxides. 
For minerals not easily deprived of their toater. — When minerals are 
present which do not give up their water wholly, even over the blast, 
as talc, topaz, chondrodite, staurolite, etc. , Penfield's simple combina- 
tion of fire-brick and charcoal oven, depicted in fig. 5, must be used, 
either with or without a retainer for fluorine, as circumstances demand. 
The part of the tube in the fire is to be protected by a cylinder of 
platinum foil tightly sprung about its end, and the part outside by 
asbestos hoard, as well as b}^ wet cloth or paper. A piece of charcoal 
