434 FOODS AND FOOD ADULTERANTS. 



the ice-cold water as before and weighed. Before weighing it should 

 be allowed to stand for one hour in the water at zero. 



Let t' represent the weight of the empty crucible in the air. 



Let t" represent the weight of the empty crucible in the water. 



Let b' represent the weight of the filled crucible in the air. 



Let b" represent the weight of the filled crucible in the water. 



Let S represent the specific gravity. Then S is computed as follows : 



= b' b" t'+t"' 



(b) In the same manner the specific gravity can be computed at 15, 

 20 or 25, or at any higher temperature at which the fat or steariue will 

 remain in solid condition. 



(c) Specific gravity by SprengePs tube. (For account of this method of 

 procedure consult Allen's Commercial Organic Analysis, vol 1, page 5.) 



Much confusion has arisen concerning the real meaning of the spe- 

 cific gravities reported for lards and lard adulterants because of failure 

 on the part of the authors to state all the conditions. All statements 

 of specific gravities should be accompanied by the temperature at which 

 they were taken and the temperature of the equal volume of water with 

 which they are compared. It would be convenient if some uniform 

 practice of stating specific gravities could be adopted by all analysts. 



(d) Notes onmethods of computing specific gravities. The rates of expan- 

 sion of lard and the fat oils used as lard were carefully studied by Dr. 

 C. A. Crainpton, and I insert here his observations thereon. 



All the determinations were made very carefully by the methods described, and the 

 figures given are in all cases the average of two or more duplicates. In the densities 

 taken at low temperatures the flasks filled with the samples were placed in a vessel 

 containing water somewhat above the temperature at which the determination was 

 to be made, and when it had dropped to this point they were carefully stoppered, taken 

 out of the vessel, allowed to cool, and weighed. The determinations at high temper- 

 ature were made by placing the flasks in an oil bath. The heat was raised *> as high 

 a point as was deemed safe, and at the temperatures used, 190 to 200 C., there was 

 scarcely a darkening of the contents of the flasks, and I am convinced that no decom- 

 position had taken place which would alter appreciably the density of the sample. 

 From the densities taken at these two widely different temperatures tbe mean in- 

 crease in density and the mean co-efficient of expansion was determined for each 

 sample. 



The formula used lor this was the one usually given in the books :* 



_D O -DO' 



~ (t' OD ' 

 in which 



DO = density at the lower observed temperature. 

 Do' = density at the higher observed temperature. 



t = lower temperature. 



f = higher temperature. 



* Watts Dictionary, Vol. Ill, p. 71.) 



