366 METHODS OF ANALYSIS 



excess of ammonium hydroxid to an aliquot, evaporate to dryness, dry to constant 

 weight at 120°-130°C. and weigh as ammonium sulphate. Calculate the sulphur 

 trioxid content of the acid and add sufficient concentrated sulphuric acid to make 

 it exactly 82.38% of SO3. The acid must be carefully protected against absorption 

 of water from the air. 



46 DETERMINATION. 



Place 20 cc. of the 38N sulphuric acid (100.92%) in a graduated, narrow-necked 

 Babcock flask, stopper, place in ice water and cool. Add slowly 5 cc. of the turpen- 

 tine. Mix the contents gradually, cool from time to time and do not allow the tem- 

 perature to rise above 60°C. When the mixture no longer warms up on shaking, agi- 

 tate thoroughly, place in a water bath and heat to 60°-65°C. for about 10 minutes, 

 keeping the contents of the flask thoroughly mixed by vigorous shaking 5-6 times. 

 Cool to room temperature and fill the flask with concentrated sulphuric acid until 

 the unpolymerized oil rises into the graduated neck. Centrifugalize 4—5 minutes at 

 about 1200 revolutions per minute, or allow to stand for 12 hours. Read the un- 

 polymerized residue, notice its consistency and color and determine its refractive 

 index. 



BIBLIOGRAPHY. 



» U. S. Bur. Chem. Bull. 152, p. 239. 



2 .1. Ind. Eng. Chem., 1915, 7: 519. 



3 Ibid.. 1914, 6:665. 



* U. 8. Bur. Chem. Bull. 162, p. 197. 



*> J. Ind. Eng. Chem.1915, 7: 681. 



"Ibid., 1912, 4:374. 



■< U. S. Bur. Chem. Circ. 94, p. 4. 



8 Am. J. Pharm., 1911, 83: 359. 



3 Trans. Roy. Soc. Edinburgh, 1885, 32: 67. 

 i« U. S. P., VIII, 1905, p. 334. 



" Stillman. Engineering Chemistry. 4th ed., 1910, p. 503. 

 « U. S. Bur. Chem. Bull. 135, p. 2(3. 

 13 U. S. Bur. Chem. Circ. 85, p. 12. 



