438 



FOODS AND FOOD ADULTERANTS. 



It will be seen that the results confirm, in the main, Allen's * conclusions in regard 

 to the generally uniform rate of expansion of all fats and oils. The average increase 

 in density in my samples would be rather lower than the figure ho gives (.00064) for 

 each degree C., as his figure was evidently calculated from the formula 



. Do-PC 1 



Kopp t gives a figure very nearly the same as mine, for the mean absolute expan- 

 sion co-efficient of olive oil, viz : .00080348. 



In the lards and oils in the above table, I also determined the density by the plum- 

 met at 4-35 C. These results, together with results'calculated from the flask deter- 

 minations. so as to make the figures comparable, are given in the following table : 



Comparison of results with plummet and with specific-gravity flask. 



This short series of comparisons adds testimony to the accuracy of the Archimedean 

 method for taking specific gravities, and it is certainly a most rapid and convenient 

 means to this end. I went through nearly the entire series of samples used in our 

 lard investigation, about 150 in all, in three days. I would call attention to a slight 

 inaccuracy in Allen's description of the method. On page 14 (Vol. II), ho says: "The 

 plummet should have a displacement of exactly 5cc (in water). This should, of 

 course, be 5 grams, otherwise ho would bo comparing rolniin- with <////</, as it is tho 

 weight of the sample displaced which is used as the numerator of the fraction of which 

 the weight of water displaced is the denominator in tho expression of its specific 

 gravity. Tho error would not bo so great where the volume and density of wafer 

 were taken as being identical at 15.5 C., but still quite an appreciable error would 

 be introduced when the determination on the sample wasmadeat35 -tor>0 C.,asona 

 fafc, for example. There is much need for more exact mathematics in calculating 

 specific gravities, and more uniformity in methods of expressing them among chemists 

 ia greatly to bo desired. 



" Op. cit., p. 20. 



tLieb. Ann., IKt, p.1'J'.. 



