EXAMINATION OF COTTONSEED OIL 25 



{a) LewkowitscK s Nitric Acid Test. — One c.c. of the 

 oil is vigorously shaken up in a test-tube with an equal 

 volume of nitric acid of specific gravity 1-37. Pure 

 cotton-seed oil gives a dark brown coloration after 

 being allowed to separate for fifteen minutes or longer, 

 while olive oil containing cotton-seed oil as impurity 

 will give lighter colours ; from the intensity of the 

 coloration some idea as to the amount of cotton-seed 

 oil present may be arrived at. 



{U) Becchi's Test. — Ten c.c. of oil are shaken in a test- 

 tube with I C.C. of an alcoholic solution of silver nitrate 

 to which a few drops of ether have been added. Ten 

 C.C. of amyl alcohol containing 1 5 per cent, of rape oil 

 (colza oil) are then added, the mixture well shaken, 

 divided into two equal parts, and one part heated on the 

 water-bath for fifteen minutes. 



The production of a dark brown colour is character- 

 istic of cotton-seed oil, although this test does not 

 always give reliable results. 



if) Halphens Test. — To i c.c. of the oil dissolved in i 

 c.c. amyl alcohol in a test-tube are added i c.c. of carbon- 

 bisulphide in which i per cent, of ground roll sulphur 

 has been dissolved.^ The mixture is well shaken, then 

 heated on the water-bath for fifteen to twenty minutes. 

 A deep red colour is produced with pure cotton-seed 

 oil, while smaller proportions of the oil in olive oil give 

 lighter colorations. 



This colour test is an extremely delicate one, and 

 is, moreover, very reliable, it failing only in the 

 case of cotton-seed oil previously heated to 200° C. 

 The test is sufificiently sensitive to detect cotton-seed 

 oil in the milk of cows fed on cotton-seed cake, and 

 is perhaps the best colour test that can be employed 



1 Flowers of sulphur should not be used, as this contains an 

 allotropic modification of sulphur which is insoluble in CS2. 



