14 TESTING MISCELLANEOUS SUPPLIES. 



2. Specific Gravity. 



Determine the specific gravity with a pyknometer, plummet, or hydrometer at 

 15.5 C. Pure gum turpentine should have a density between 0.862 and 0.875. 

 Wood turpentine may, however, range from 0.860 to 0.910 or even higher. 



3. Distillation. 



Connect a distilling flask of 150 cc capacity with a condenser having a ther- 

 mometer. Introduce 100 cc of turpentine and heat with a Bunsen burner. The 

 initial boiling point should be about 156 C., and 95 per cent should distil over 

 between 153.5 and 165.5 C. 



4. Residue on Evaporation. 



Evaporate 10 grams on the steam bath; the residue should be less than 2 

 per cent. 



5. Refractive Index. 



Determine with a Zeiss direct reading refractometer at 20 C. The index of 

 refraction for gum turpentine should be from 1.4690 to 1.4740; for wood tur- 

 pentine, 1.4685 to 1.5150. 



6. Action of Sulphuric Acid (Polymerization). 



Measure 6 cc of turpentine in a stoppered, thin-walled tube graduated to 0.1 

 cc (carbon tubes). Place the tube in cold water and pour in slowly a mixture 

 of four parts of strong sulphuric acid and one part of fuming sulphuric acid. 

 Add the acid slowly, and avoid an excessive rise in temperature. Shake the 

 tube so as to mix the turpentine and the acid, add finally about 20 cc of the 

 acid, stopper the tube, mix thoroughly, cool, allow to stand thirty minutes, and 

 note the volume of unpolymerized oil that collects on top of the acid layer. 

 Then let stand for eighteen hours and again note the volume. A pure turpen- 

 tine should show less than 0.3 cc unpolymerized at the end of thirty minutes, 

 and less than 0.5 cc after eighteen hours. 



This method will indicate gross adulteration, but will not detect admixtures 

 of very small amounts of mineral oil. Donk has perfected a method which 

 determines the presence of as little as 1 per cent of mineral oil in turpentine. 

 This method is as follows : 



Sulphuric acid of 38 times the normal strength (101.5 per cent) is prepared 

 by mixing very strong sulphuric acid with fuming sulphuric acid. It must be 

 determined by titration that this reagent is of the exact strength required, for 

 with 37.5 times normal acid (100 per cent) the turpentine is not completely 

 destroyed, and with .-u-id stronger than 101.5 per cent the amount of mineral 

 oil dissolved becomes excessive. 



Place about 25 cc of the special sulphuric acid in a flask having a narmw 

 graduated neck (n Babcock bottle does very well), cool in ice water, add 5 cc 

 of tlie turpentine to be tested and cool the flask again, shaking it carefully and 

 :n. hi ing any excessive rise in temperature by frequent cooling. The flask 

 should m>\vr !< too hot to hold in the palm of the hand. Then place it in a 

 bath of cold water and heat the bath at such a rate that in about five minutes 

 the tempera MI iv will lu> 65 C. During the heating shake the bottle about every 

 fifty seconds, finally shaking very thoroughly so as to insure the contact of 

 p:irtir|(> of the sample with the acid. Cool to room temperature and add 

 ordinary strong sulphuric acid in sufficient amount to bring the unpolymerized 

 li'inid up in tin- graduated neck. Let stand over night or whirl in a centrifuge 

 and read the volume oil the neck. 



