LARD AND LARD ADULTERATIONS. 461 



rnent be .903, then the number of cubic centimeters required to weigh 5 

 grams would be 5-j-.903=5.54cc. In a case of that kind, therefore, o.Gcc 

 of the fat should be measured into the flask and its weight accurately 

 determined. 



Certain precautions are necessary in weighing the samples of fat in 

 order to secure uniform results. Since the temperature at which the 

 fat is manipulated must be kept approximately at from 35 to 40, the 

 method, of weighing from a weighing-bottle is objectionable. Not only 

 is it difficult to gauge the amount poured out from the weighing-bottle, 

 but the falling temperature influences considerably successive weights. 

 The samples should therefore be weighed in the flasks in which the 

 saponitication is to take place. In case this is done in an Erlenmeyer 

 flask, it can be placed directly upon the pan of the balance. If the 

 round-bottom flasks are used, however, they may either be held in a 

 light beaker glass on the pan of the balance or suspended from a hook 

 of the balance by a linen thread. The flasks in which the weighings 

 are to be made should not be wiped with a towel or silk handkerchief 

 within fifteen minutes of the time the weight is taken. It is best in 

 weighing these flasks to remove the desiccating material from the inte- 

 rior of the balance, so as to avoid changes in the amount of moisture 

 deposited on the sides of the flask during the time the weighing takes 

 place. The flask should stand in or near the balance for not less than 

 fifteen minutes before the weighing is made. The flask should be 

 counterpoised on the weight-pan of the balance by a duplicate flask 

 treated in the same way. The empty flask having been weighed, it is 

 removed from the balance and a measured quantity of the fat run into 

 it from a graduated pipette. The flask is now replaced upon the pan 

 of the balance or suspended from a hook by a linen thread, as before 

 described. The reweighing of the flask should not take place before 

 five minutes, so that the fat may have time to cool. 



Example. Grams. 



Weight of flask counterbalanced 4.3611 



Weight of flask plus fat 9.3711 



Weight of fat 5.0100 



In the above case the weight of fat which was required was 5 grams, 

 and the amount as measured, as seen by the above results, was almost 

 exactly that required. At the end of the operation the results can be 

 calculated to exactly 5 grams by simple proportion. 



(b) Saponification equivalent. About 2.5 grams fat (filtered and free 

 from water) are weighed into a patent rubber-stoppered bottle or flask, 

 as described above, and 25cc approximately semi-normal alcoholic pot- 

 ash added. The exact amount taken is determined by weighing a small 

 pipette with the beaker of fat, running the fat into the bottle from the 

 pipette, and weighing beaker and pipette again, or the method described 

 above may bo used. The alcoholic potash is measured always in the 

 same pipette, and uniformity further insured by always allowing it to 



