40 
SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
is likewise laid on the tube, as well as beneath and behind, and the 
blast flame is given a horizontal direction, so as to play upon the side 
of the apparatus. In this way a most intense temperature can be 
reached. 
In whichever way the apparatus may be used, the water found is 
Fig. 5.— Penfleld's fire-brick and charcoal oven for use in determining water. 
the total water, from which that found separately at 105° C. may be 
deducted if desired. 
DIRECT WEIGHING OF THE WATER IN ABSORPTION TUBES. 
PenfieWs procedure. — The simplest of these methods as to apparatus, 
and one permitting, by the use of auxiliary arrangements such as 
are shown and described on page 37, the determination of the hygro- 
scopic as well as any other fraction of the water, is the following glass- 
tube arrangement (fig. 6) of Dr. Penfleld's, 1 whereby the brick and 
charcoal oven already referred to (fig. 5) comes again into play, but 
without the half brick shown in that figure. 
The tube is of about 15 mm. internal diameter, and is fitted with 
two platinum cylinders at A, one inside, the other outside, where the 
heat exposure is to be most intense. 
These are made from pieces of platinum foil, about 0.07 mm. in thickness and 
8 by 11 cm. in diameter, which have been previously bent around glass tubes of such 
U 
Fig. 6.— Tube for water determination according to Penfield. A, outer protecting covering of plati- 
num foil. A second similar foil on the inside prevents the glass from collapsing when heated to 
softness. 6, cross section of platinum boat. 
a size that when applied to the combustion tubing the spring of the metal will hold 
them in place. A large platinum boat, 7 to 8 cm. long and 11 to 12 mm. in diame- 
ter, with a cross-section like b, should be used, since this will readily hold a gram 
of mineral mixed with 5 grams of sodium carbonate. * * * The tube is placed 
in the angle formed by the charcoal lining, some pieces of charcoal are placed at the 
sides in front, leaving an opening through which the flame may be directed, and an 
additional piece is laid on top. The tube can readily be brought to a full white heat, 
'Am. Jour. Sci., 3d series, Vol. XLVIII, p. 37, 1894; Zeitscb. fiir anorg. Chemie, Vol. VI, p. 22, 1894. 
