BULLETIN 56, U. S. DEPARTMENT OF AGRICULTUEE, 



120° in less than 15 minutes, the flame should be turned down, 

 so that the temperature will rise approximately 5 degrees a minute. 

 If it takes more than 15 mmutes to reach 120°, the flame may 

 be turned up, so that the temperature wUl rise at the rate men- 

 -^ tioned. The temperature of the oil in the 

 inner flask should rise from 120° to 150° in 

 approximately 6 minutes. If the oil between 

 the walls is not emptied and another test is 

 made before the oil gets cool, the time required 

 to reach 120° will be less than 15 minutes with 

 a proper flame. 



METHOD OF FINDING THE PROPER TEMPERA- 

 TURE. 



The proper temperature at which to extinguish 

 the flame in the apparatus was found by check- 

 ing duplicate samples in the common type of 

 double-walled water oven that was 11 mches 

 high, 11 inches wide, and 10 inches deep, outside 

 ^ „ „, . , dimensions, and having a 1-mch space between 



Fig. 6.— Strainer for reeov- . ' _ o ^ 



ering the oil. the outer- and the inner wall for the water. 



The water in the oven was kept boiling by two gas flames and was 

 kept at a uniform height. The different substances were allowed to 

 remain in the oven until they came to a constant weight. 



Fig. 7. 



-Rubber stoppers, showing the effect of heat when tested in a copper flask. Stopper A was 

 tested unce, B 30 times, and C'ouce. 



POINTS TO REMEMBER. 



(!) Both in the inner flask and Ix'tween the two walls 150 c. c. of 

 oil should be used. 



(2) The thermometer in the copper flasks can be easily adjusted 

 by so placing the bulb of the thermometer in flour or meal that a thin 

 coating is left upon it. The thermometer is put into the flask and 



