MODIFIED METHODS OF ANALYSIS. 29 



REFRACTIVE INDEX. 



Determine the refractive index with a Zeiss direct reading re- 

 fractometer at 20 C. 



DETECTION OF ROSIN SPIRITS. 1 



Note the initial distilling temperature and to one portion of the 

 first fraction distilling below 160 C. (320 F.) add sulphurous acid 

 and to another hydrochloric acid. An initial distilling temperature 

 below 154 C. (309 F.), together with the development of a decided 

 red color with sulphurous acid and a green color with hydrochloric 

 acid, when accompanied by a polymerization residue of less than 5 

 per cent on the original sample, is indicative of rosin spirits. Re- 

 fractionate 50 to 100 cc of the first fraction, distilling below 160 C. 

 (320 F.) with a column, note the initial distilling temperature, and 

 repeat the color and polymerization tests. If they are more positive 

 than before, rosin spirits is probably present. 



DETECTION OF COAL-TAR OILS. 1 



To 150 cc of sulphuric acid (4:1) in a separatory funnel, add 100 cc 

 of the suspected turpentine, being careful to prevent a rise in tem- 

 perature above 40 C. Mix thoroughly, keeping the temperature 

 below 40 C. (104 F.), draw off the polymerized portion, transfer 

 the unpolymerized portion to a small distilling flask, and distill 

 slowly, stopping the distillation when the temperature reaches 

 180 C. (346 F.), or before if the distillate becomes cloudy, colored, 

 or oily. Determine the refractive index, which should be 1.475 or 

 more, and add cautiously a little nitric acid. The odor of nitro- 

 benzol or nitro-xylol proves the presence of coal-tar oils. 



DETECTION AND ESTIMATION OF MINERAL OIL. 



The method used for the detection and estimation of mineral oil 

 is an improvement of the Hertzfeldt method of polymerization with 

 sulphuric acid and is based on the fact, observed by Mr. Donk, that 

 the residue from turpentine is practically constant and negligible if 

 the acid used is of a certain exact concentration. The method has 

 been in use in this laboratory for about three years with perfectly 

 satisfactory results. 



Preparation of add. The sulphuric acid used is 38 times normal. 

 This solution contains 100.92 per cent of sulphuric acid by weight 

 and is prepared by adding fuming acid to the concentrated until a 

 strongly fuming mixture is obtained. The exact strength is then 

 determined by diluting and titrating a weighed portion (6 to 8 

 grams), using methyl orange as indicator. An accurate determina- 

 tion of the acid strength is absolutely necessary, as an acid contain- 



1 See page 19 for further details as to the determination of these adulterants. 



