2 BULLETIN 56, U. S. DEPARTMENT OF AGRICULTURE. 
DESCRIPTION OF THE SPECIAL FLASK. 
The flask, the dimensions of which are shown in figure 1 , is double 
walled and can be made of copper or glass. The inner flask has a 
capacity of approximately 900 cubic centimeters and the space 
^ between the two walls should hold not less 
than 250 nor more than 300 c. c. If the flasks 
are made of copper, the thickness of the 
copper before it is spun should be 22 thou- 
sandths of an inch or 16 ounces to the 
square foot. The copper flasks will have 
to be made in two sections and soldered 
together in the middle with a very hard 
solder. The soft solder commonly used by 
plumbers is nob suitable for this work. 
Success with these flasks has been attained 
only when they were soldered together with 
a silver solder. The neck of the flask must 
be of but one thickness of copper, for if it is 
too heavy it will melt 
the rubber stoppers. 
The glass flasks 
when made in ac- 
cordance with the 
proper specifications 
will give as accurate 
results as the copper 
ones. They should 
be made of the best 
grade of resistant 
glass and well an- 
nealed, and the necks 
should be sufficiently 
heavy to stand tight 
corking. When 150 
c. c. of oil is poured 
in between the two 
walls, the top of the oil should be about halfway up the sides of the 
flasks. If the flasks do not meet these specifications they should not 
be used. 
Fig. 1. 
A distillation flask, showing its dimensions and the correct 
adjustment of the thermometer. 
HOW TO MAKE A WATER TEST OF FLOUR OR MEAL. 
To make a water test pour 150 c. c. of oil in the inner flask and then 
150 c. c. of oil between the two wallsT Weigh an average sample of 
50 grams on scales that are sensitive to at least one-twentieth of a 
