420 FOODS AND FOOD ADULTERANTS. 



(b) Melting point. Since cotton oil solidifies only at a temperature 

 near or below the freezing point of water its melting point has not 

 been determined. 



(c) Color reaction. The color produced in cotton oil by sulphuric and 

 nitric acids is a characteristic mark of the greatest value. This color 

 varies from deep reddish brown to an almost black color. Some of the 

 descriptions of the color produced in cotton oil, taken from the note- 

 book, are as follows: "dark brown," "very brown black," "deep red 

 browE " very red," "yellow brown," etc. It must not be forgotten, 

 however, that these colors can be produced by other oils, and hence 

 their occurrence is not conclusive evidence of the presence of cotton oil. 



(d) Refractive index. The refractive index of cotton oil is distinctly 

 higher than that of lard. The variation in the index of refraction is in- 

 versely as the temperature. The mean rate of variation for each de- 

 gree is .000288. For a temperature of 25 the mean refractive index of 

 the samples examined was 1.4674. The rate of variation in the index 

 of refraction in cotton oil is sensibly the same as that for lard. 



(c) Rise of temperature with sulphuric acid. The rise of temperature 

 which cotton oil suffers when mixed with sulphuric acid is a very promi- 

 nent diagnostic sign. In the samples examined the lowest increment 

 of temperature noted was 80.4 and the highest 90.2. The mean rise of 

 temperature was 85.4. Cotton oil, therefore, gives more than double 

 the increment of temperature shown by pure lard under the same con- 

 ditions. 



(/) Crystallization point of fatty acids. Since cotton oil is fluid even at 

 low temperatures (viz, 0) the determination of its melting point is 

 only a matter of scientific interest. The point at which its free acids 

 crystallize is, however, easily determined according to the method of 

 Dalican. 



Degrees. 



The mean crystallizing point of the acids examined was 3:>. ~> 



The minimum was :i(l - ' 



The maximum was 35. (5 



The high temperature reached in the crystallization of the fat acids 

 is a peculiar characteristic of cotton oil. In lard there is not a very 

 great difference between the temperatures indicated by the melting 

 point of the glycerides and the crystallizing point of the fat acids. In 

 cotton oil, however, these temperatures are widely removed. 



(y) Melting point of fatty acids. The melting point of the free acids 

 of cotton oil was determined both in capillary tubes and by observing 

 the deportment of the add on the bulb of a delicate thermometer pro- 

 tected by a glass Mask. The two sets of data were almost identical. 



Degree*. 



The menu inciting ; |oh il, of the .-iritis examined was ._ 



Maximum ' ' ' 



Mini mil in :>>1 - () 



