42 



FOODS AND FOOD ADULTERANTS. 



Jones 1 calls attention to the fact that the specific gravity of butter 

 increases with age. 



The specific gravities of several samples are compared in the following 

 table, the numbers in second column being obtained after eighteen 

 months :. 



Specific gravity at 37.7 C. 



In other samples there was a decrease in specific gravity. In five 

 samples out of nine there was an increase and the percentage of soluble 

 acids had also increased. 



Since butters in general are obtained for analysis without having 

 been long kept the observation of Jones does not have much practical 

 importance. 



Sendtuer and Hilger 2 find that a filtered pure butter fat does not 

 show a specific gravity less than .860 at 100 0. In the Erlangen Uni- 

 versity numerous experiments with twenty different samples of butter 

 showed variations from .860 to .8085. 



Allen 3 recommends Sprengel's tube for the determination of specific 

 gravity of oils at the temperature of boiling water. 



The weight of the Sprengcl tube and that of water contained in it at 15. 5 C. bring 

 known, the tube should bo completely filled with the oil by immersing one of the 

 orifices in the liquid and gently sucking the air from the other orifice of the tube. 

 The tube is then placed in the mouth of a conical flask containing water kept in a 

 rapid ebullition, and the cover of a porcelain crucible placed over it. As the oil gets 

 hot it expands and is expelled in drops from the horizontal capillary orifice of the 

 tubes. When the expansion ceases any oil adhering to the orifice is removed by 

 cautious application of filter paper, the tube removed from the bath, \vipod dry, al- 

 lowcd to cool, and weighed. The weight of the contents divided by the weight ol 

 water at 15. 5 C. previously known to be contained by the tube will give the density 

 of the oil at tho temperature of the boiling water ; water at lo.5 C. being taken as 

 unity. 



Bendikt 4 prefers the Sprengel tube to all the other methods of esti- 

 mating the specific gravity of oils. He also recommends the Westphal 

 balance as used by Bell and Walkenhaar. 



1 Analyst, 1879, p. 39. 



- Vcreinbarnugen betreffs d. Untcrsuch. n. Bcnrteiluug v. Nahrungs-GenuRStnittelu, 

 pp. 221-2. 



3 Com. Organic Analysis, Vol. 2, 2d ed..p. 15. 



4 Analyse der Fette, &c., p. 53. 



