18 COMMERCIAL TURPENTINES. 



called, as improved by Mr. Donk and conducted in the Bureau of 

 Chemistry, is as follows: 



Place approximately 25 cc of exactly 38 times normal sulphuric acid in a flask 

 holding approximately 50 cc and having a graduated neck. The ordinary Babcock 

 milk-test bottle serves admirably, and being a stock article is readily obtainable. Cool 

 the flask in ice and run in without mixing 5 cc of the turpentine to be tested. If 

 the turpentine is pure and recently distilled, the charred surface will have a green 

 fluorescence when held to the light and the underlying sulphuric acid will be clear 

 and slightly colored. As little as 5 per cent of mineral oil prevents the green fluores- 

 cence and gives the sulphuric acid a muddy appearance. Gum and wood turpentine 

 containing considerable quantities of heavy terpenes also lack fluorescence and are 

 muddy in appearance. Mix the turpentine with the acid by cautious shaking, 

 keeping the temperature below 65 C. (149 F.) by frequent immersion in ice. When 

 the temperature no longer increases on shaking (determine by the touch), shake vig- 

 orously to insure perfect contact between the acid and the turpentine, place the flask 

 in water at about 40 C. (104 F.), and heat slowly to 65, shaking vigorously and fre- 

 quently. When this temperature is attained, give a final vigorous shaking; cool, 

 bring the unpolymerized layer into the neck by running in ordinary sulphuric acid, 

 centrifuge or let stand for two hours, read the volume of unpolymerized clear top 

 layer and immediately determine its refractive index, withdrawing a portion from 

 the top of the clear layer only for this purpose. The character and quantity of this 

 layer or residue will show whether or not the turpentine is adulterated with mineral 

 oil. If the turpentine is pure, the residue will seldom exceed 1 per cent; it will be 

 very viscous, and will have a refractive index at 20 C. of 1.5000 to 1.5200. If the 

 sample contains mineral oil, however, the residue will be limpid or oily and colorless 

 and will have a refractive index at 20 C. between 1.4200 and 1.4950. 



It is characteristic of mineral oils that the refractive index of the 

 unpolymerized oil is lower than that of the original sample, while 

 that of the residue from turpentine is higher. The results are not 

 quantitative, as when 5 per cent of mineral oil is present approxi- 

 mately 80 per cent of it is taken up by the sulphuric acid, when 10 

 per cent of mineral oil is present approximately 60 per cent, and 

 when 20 per cent is present approximately 50 per cent of mineral oil 

 is destroyed in polymerization. When a straight mineral oil is 

 treated with the 38 normal sulphuric acid, about 25 per cent of it is 

 acted upon. For kerosene these figures are much lower. In this 

 report residues greater than 1 per cent are considered to be mineral 

 oil and no correction is made for the amount destroyed in polymer- 

 ization. These results are therefore low, giving the benefit of the 

 known action of the acid on the mineral oil entirely to the seller. 



In a number of instances when the volume of the residue after 

 polymerization did not indicate the presence of mineral oil but its 

 refractive index or limpidity did, the turpentine was distilled, and the 

 portion which did not distill below 170 C., and several of the frac- 

 tions from the distillation were subjected to the sulphuric-acid test. 

 As a rule, the portion which did not distill below 170 C. left more 

 residue after polymerization than the original turpentine did and it 

 possessed more decidedly the characteristics of mineral oil, i. e., low 



