BENZIN AND LIGHT PETROLEUM OILS. 15 



Pure turpentine should leave ;i residue <>f not over 0.04 cc, which is not 

 limpid and which has a refraetive index of not less than 1.r>00. 



If the unpolyinerized residue is 0.04 cc or less, mineral oil may be assumed 

 to be absent. If the residue is greater, calculate from It the percentage of 

 mineral oil present. This will be, of course, only approximate, for there is 

 some residue from pure turpentine and some mineral oil is dissolved by the 

 acid; but for all practical purposes it may be assumed that the errors balance 

 one another, and hence it is not advisable to apply any correction. 



7. Spot Test. 



Place a drop on filter paper and allow it to dry at room temperature; It 

 should leave no stain. 



8. Flash Point. 



Support a crucible, such as is used in determining the flash point of linseed 

 oil, in a vessel of water at 15 to 20 C. ; the water should cover about two- 

 thirds of the crucible. Fill the crucible to within about 2 cm of the top with 

 turpentine, insert a thermometer, and heat the water bath slowly, 1 per minute. 

 Begin at 37 and test for the flash at each rise of 0.5. The turpentine should 

 not flash under 40.5 C. 



BENZIN AND LIGHT PETROLEUM OILS. 



The term benzin is used for a number of light petroleum oils. In the paint- 

 ing trade it generally refers to a product of about 62 Baum6 (0.7292 sp. gr.). 

 The petroleum benziu of the U. S. Pharmacopoeia is a lighter oil, being a light 

 gasoline. 



1. Specific Gravity. 



Determine with a spindle, pyknometer, or plummet at 15.5 C. The deter- 

 mination can be made at room temperature and corrected to 15.5 C. 



2. Sulphur (Sodium Nitroprussid Test). 



To 100 cc of the sample in a flask add about 1 gram of bright metallic sodium, 

 connect with a reflux condenser, and boil for one hour. Cool, add water drop 

 by drop until the metal is dissolved, separate the aqueous liquid, and test 

 with a drop of sodium nitroprussid solution. A fine violet-blue coloration indi- 

 cates sulphur. 



3. Sulphur Compounds and Pyrogenous Products (U. S. P. Test). 



To 100 cc of the sample add 25 cc of a solution of 10 per cent anhydrous 

 ammonia in 95 per cent alcohol (spirit of ammonia U. S. P.), add 1 cc of silver 

 nitrate solution. Boil gently for five minutes. A brown coloration indicates 

 sulphur compounds or pyrogenous products. 



4. Residue on Evaporation. 



Place 25 cc in a 100 cc platinum dish, heat on steam bath for thirty min- 

 utes, and weigh residue. No residue should be left by this test. 



5. Fractional Distillation. 



Light petroleum oils are usually tested only for specific gravity ; but as light 

 and heavy distillates may be mixed, the specifications would be improved by 



