14 OLEORESINS OF SOME WESTERN PINES. 



161.3; ether number, 12.5. The specific rotation of the rosin was 

 determined for an alcoholic solution, using the formula [a] D = r~rT 

 in which 



a= 0.66, the optical rotation in a 1-decimeter tube at 20 C. 



Z=l, the length of the tube in decimeters. 



p = 6.22, the number of grams of the substance in 100 grams 



of the solution. 



d = 0.8239, the density of the solution. 

 Therefore, the specific rotation, [a] D = -12.88. 

 The coarsely powdered rosin was digested with twice its weight 

 of alcohol containing 25 per cent concentrated hydrochloric acid. 

 The residue yielded about 90 per cent of crude crystals. These crys- 

 tals, recrystallized from acetone until white, melted at 159 to 160; 

 the specific rotation, [a] D , is computed from the following values : 

 a=- 2.61 p = 4.06 [a] D = -78.44 



Z= 1 d = 0.8196 



When allowed to crystallize slowly from dilute acetone and exam- 

 ined under the microscope, the crystals had the exact crystalline 

 form figured by Schkateloff, 1 Mach, 2 and Levy 3 for abietic acid. By 

 rapid crystallization they have the form of triangular plates. This 

 form can be readily obtained by dissolving the abietic acid crystals 

 in acetone and adding water to the solution until it is turbid; as it 

 cools, a mass of crystals immediately forms. 



In order to confirm the presence of abietic acid the silver salt of 

 the resin acid was prepared in the manner described on page 1 1 , and 

 its silver content determined. The results of the analysis were: 



Per cent. 



0.1396 gram silver salt gave 0.0365 gram silver=26. 15 

 .1120 gram silver salt gave .0295 gram silver=26. 34 



Mean =26. 25 



Silver abietate, Ag(C 20 H 29 O 2 ), requires 26.37 per cent of silver. 



Schkateloff 's 4 method of precipitating the resin acids works very 

 well for the rosin of Pinus ponderosa. It consists in saturating an 

 alcoholic solution of the rosin with sulphur dioxide. The resin acids, 

 which crystallize out on cooling, are white and much purer than 

 those obtained by crystallizing from alcohol and hydrochloric acid. 

 No " bleaching" of the color of the alcoholic solution, which Schka- 

 teloff noted, was observed, even though the gas was passed in for two 

 hours. 



Some of the original rosin was dissolved in acetone and allowed to 

 stand in an ice box overnight. The crystals obtained were purified 



1 Monit. Scientif., p. 218, vol. 22, 1908. * Berichte, p. 3044, vol. 39, 1906. 



2 Monatsh. f. Chem., p. 629, vol. 15, 1894. < Monit. Scientif., p. 223, vol. 22, 1908. 



