64 
BULLETIN 1216, L T . S. DEPARTMENT OF AGRICULTURE. 
To determine the amount of residue, the flask is weighed again 
when distillation is complete. During the distillation the con* 
denser tube shall be warmed when necessary to prevent the depo- 
sition of any sublimate. The percentages of fractions shall he 
reported by weight. 
rr^ 
PlO. 6. — Distillation apparatus. 
DETERMINATION OF PERCENTAGE OF RESIDUE OF 
DESIRED PENETRATION. 
Fifty grams of the oil are placed in a 3-ounce deep, seamless 
tin box; the box is placed in a sand bath and heated over a 
Hansen burner. A thermometer Is suspended in the oil, the bulb 
not touching the bottom of the box. The temperature of the oil 
is kept at from 249° to 260° 0. (480° to 500° F.) and the oil is 
Stirred from time to time with the thermometer to prevent over- 
heating in any part. Depending upon the nature of the oil, as 
usually indicated by its flash, consistency at 25° C. (77° F.). and 
specific gravity, the operator can with experience tell about what 
percentage if will be necessary to evaporate before cooling and 
taking a penetration of the residue. It is sometimes necessary to 
make several trials before the desired result Is obtained. When 
the required penetration is reached, the residue left from evapora- 
tion is weighed and its per cent of the original sample taken is 
computed. 
