648 ANNUAL REPORT OF THE Off. Doc. 



bottles when they are whirled, but in case of the breakage of 

 bottles may protect the face and eyes of the operator from injury by 

 pieces of glass or hot acid. The machine should be frequently 

 examined to make certain that there is no slipping of belts or 

 frictional bearings which may cause too slow motion and result in 

 an imperfect separation of the fat. Managed in this way no extra 

 heat is required, as that caused by the chemical action is sufficient 

 to keep the fat liquid. If the bottles have stood, after the acid 

 is added, until the contents are cooled below 100 degrees F., they 

 should be warmed to about 200 degrees F. by placing them in hot 

 water before whirling. 



(2.) Filling the Bottles with Hot Water. — As soon as the bottles 

 have been sufiiciently whirled, they should be filled only to the neck 

 with hot water. If practical, distilled or rain water should be used 

 for the purpose. The bottles are most conveniently filled by placing 

 a vessel containing boiling water above the machine, and by moans 

 of a syphon made from a small rubber tube with a glass tip, run 

 the water directlv into the bottles without removing them from 

 the wheel. The flow of water can be perfectly controlled by a 

 pinch-cock upon the rubber tube. If only a few tests are to be 

 made, the bottles may be easily filled with a pipette, or by pour- 

 ing from a graduate. The cover should then be replaced and the 

 machine turned for about one minute, after which the neck of each 

 test bottle is filled with hot water to the upper limit of the scale 

 or nearly so, and the whirling is then repeated for another minute. 

 Unless the hot water is added in two portions, the fat is often apt 

 to be mixed with particles of various impurities, which render 

 the reading uncertain. 



84. Measuring Amount of Fat. 



After the last whirling is completed, the test bottles are removed 

 from the machine and placed in water which has a temperature 

 between 140 degrees and 150 degrees F. The per cent, of fat is 

 read at this temperature. To measure the fat, hold the test bottle 

 upright, having the graduated scale on a level with the eye; notice 

 the divisions which mark the highest and lowest limits of the fat. 

 The difference between gives the per cent, of fat directly. The read- 

 ing can easily be taken to half divisions or to one-tenth of one per 

 cent. 



The line of division between the fat and the liquid beneath 

 is nearly a straight line and no doubt need arise concerning the 

 reading at this i)oint, but, the upper surface of the fat being 

 concave, errors often occur by reading from the wrong place. The 

 reading should be taken at the line where the upper surface of 



