416 FOODS AND FOOD ADULTERANTS. 



tious are as follows : "Brownish pink," "trace of yellow," "market! 

 .red brown," "no color," "slight coloration, etc. 



(d) Refractive index. The deviation produced in the direction of a 

 ray of light in passing through a film of melted fat is also a valuable 

 physical characteristic. This deviation is usually measured as the quo- 

 tient r l the sine of the angle of incidence divided by the sine of the angle 

 of refraction and is kuowu as the refractive index. The refractive index 

 of pure water, at 25 on the instrument used in these investigations was 

 1.3300. The refractive index of the samples of lard was made at as low 

 a temperature as possible to preserve fluidity, viz : between 30 and 3G. 

 In the tables the temperature at which the index was taken is not given, 

 but the number representing the index corrected to the uniform temper- 

 ature 25. The rate of variation in the refrative index for each degree of 

 temperature, experimentally determined, for lard oil was .000288. This 

 number may also be taken to represent the variation for lard. The re- 

 fractive index varies inversely as the temperature. The mean number 

 for a pure lard at 25 is about 1.4G20. The variation from this number 

 can be seen in the analytical tables which follow. The refractive index 

 of pure lard is distinctly less than that of cotton-seed oil at the same 

 temperature, and is therefore a valuable characteristic for analytical 

 purposes. 



(e) Rise of temperature icith sulphuric cid. More valuable for di- 

 agnostic purposes than the physical properties already considered is 

 the rise of temperature which lard undergoes when mixed, under proper 

 conditions, with sulphuric acid. -There is such a marked difference be- 

 tween the numbers representing the rise of temperature in pure lard 

 and those of the adulterants usually employed in the manufacture of 

 mixed lard as to give this number a high analytical value. With 

 steam lards, ten samples, the extremes, as registered by the thermom- 

 eter, were 38.8 and 42.1. For pure lards of miscellaneous origin, one 

 from Deerfoot Farm, Southborough, Mass., gave a rise of temperature 

 37.1, and a pure leaf lard from S perry & Barnes, New Haven, Oonn., 

 a rise of temperature of 46.2. 



The value of this characteristic is so great as to lead me to expect ap- 

 proximately reliable quantitative results from a general determination 

 of the actual amount of heat produced in an appropriate calorimeter. 

 I am at present attempting to devise an instrument by which the actual 

 number of calories produced by mixing definite quantities of fats and 

 oils and sulphuric acid can be accurately determined. 



(/) Crystallization point of fatty acids. The method described in the 

 work of Dalicau for determining the crystallizing points of fatty acids 

 gives valuable data concerning the nature of pure lard, and also of the 

 relative amount of stearic and oleic acids present in the mixture. The 

 crystallizing point was found to vary in the ten samples of prime steam 

 lard already mentioned from 35.4 to 30.5. In pure lards of other 

 kinds the variation was found to be from 32.1 to 42.7. 



