MODIFIED METHODS OF ANALYSIS. 31 



(As the destruction of the turpentine deperds upon its contact 

 with the sulphuric acid, which in turn is dependent upon the minute- 

 ness of the turpentine particles suspended in the acid, it follows, and 

 this is convincingly borne out by experience, that thorough mixing 

 is one of the salient features of the method.) 



Cool to room temperature, add ordinary sulphuric acid until the 

 contents rise in the graduated portion of neck, and whirl at 1,200 

 revolutions per minute for three or four minutes, or allow to stand 

 over night; read the amount of supernatant residue. 



Discussion. With a pure turpentine the residue will be straw 

 colored, viscous, and if read at once will give a refractive index at 20 

 C. of 1.5050 or higher and amount to from 0.02 to 0.05 cc. When 

 adulterated with mineral oil the residue is a limpid, colorless liquid, 

 having a refractive index of 1.4900 to 1.4300 or lower, depending on 

 the kind and amount of adulterant present. When a small amount 

 of adulterant has been added it is preferable to use a centrifugal 

 machine reading the refractive index immediately, using the upper 

 portion of the residue, as the mineral oil and residual turpentine are 

 thus stratified, the low-reading mineral oil constituting the upper 

 portion. A capillary pipette is used in transferring a small portion of 

 the residual oil to the refractometer. 



The results are always low, as members of the unsaturated aliphatic 

 series are partly soluble in the acid used. When a mineral oil of an 

 asphaltum base has been used as an adulterant, results are usually 

 approximately too low by from 80 to 50 per cent. That is the percent- 

 age of mineral oil present that is polymerized by acid of the strength 

 employed or that remains mixed with the acid is higher with low 

 percentages of mineral oil and lower with high percentages. The 

 method has been in use in this laboratory for several years in con- 

 nection with pure food and drug work as well as in testing turpentine, 

 paint, varnish, oils, etc., bought under Government contracts, and 

 an experienced operator following the method strictly has no difficulty 

 in detecting 2 per cent of adulterant. 



