20 COMMERCIAL TURPENTINES. 



carefully refractionated, the initial distilling temperature noted, and 

 the refractive index, behavior with sulphuric acid (color, heat devel- 

 oped, refractive index of residue, if any), and odor closely observed. 

 An initial distilling temperature of less than 154 C. (309 F.) with 

 a refractive index of the first fraction of more than 1.475, together 

 with a reddish color and but little development of heat on mixing 

 with the sulphuric acid, and the characteristic odor of the oils, is proof 

 of the presence of coal-tar oils. 



When the proportion of coal-tar oils is small, this examination may 

 not always give positive evidence of their presence. As little as 5 

 per cent of xylol, however, may be identified by the following 

 procedure: 



To 150 cc of 4 to 1 sulphuric acid, in a separatory funnel, add 

 100 cc of the suspected turpentine, being careful to prevent a rise in 

 temperature above 40 C, (104 F.). Mix thoroughly, keeping the 

 temperature below 40 C., draw off the polymerized portion, transfer 

 the unpolymerized portion to a small distilling flask, and distill 

 slowly, changing the receiver when the distillate ceases to be clear, 

 colorless, and limpid. The temperature at this time should not 

 exceed 180 C. (356 F.). A turpentine containing 5 per cent of 

 xylol, when treated in this way, gave about 3 cc distilling below 

 180 C. (356 F.). The refractive index was 1.475, the odor that of 

 xylol, and on adding nitric acid a strong odor of nitro-xylol was- 

 obtained. This treatment of turpentine with dilute sulphuric acid 

 converts it into a heavy oil (with a refractive index of 1.5 + ), and 

 not more than a few cubic centimeters will distill from ,the mixture 

 below 300 C. (572 F.). The method has not so far been sufficiently 

 developed to be of quantitative value, so that the proportion of coal- 

 tar oils present can only be approximated within wide limits. 



Nonvolatile oils are, of course, readily detected by distillation, and 

 their nature, so far as it may be determined, is learned by the usual 

 methods. 



DISCUSSION OF DATA ON UNADULTERATED SAMPLES. 



It will be observed in studying the detailed analytical data that a 

 few samples, which undoubtedly do not contain added adulterants > 

 show some inconsistencies among the figures for specific gravity , 

 refractive index, and behavior on distillation. While, as has been 

 mentioned, this fact is partially accounted for by the use of emergent 

 stem thermometers and the variation in barometric pressure, it is 

 certainly not always due entirely to these causes, but also partly to 

 the fact that, in examining so large a number of samples, it was imprac- 

 ticable to make all the determinations on each sample at one time, 

 and changes occurred in these few turpentines in the time that elapsed 

 between the beginning and the ending of their analysis. For some of 



