BULLETIN 56, U. S. DEPARTMENT OP AGRICULTURE. 



DESCRIPTION OF THE SPECIAL FLASK. 



The flask, the dnnensions 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 not 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 

 J- will give as accurate 

 !j^ results as the copper 

 I- 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 oU between the two walls. Weigh an average sample of 

 50 grams on sca,les that are sensitive to at least one-twentieth of a 



