It is noteworthy that the angle of rotation decreases with age. Comp. p. 26, footnote 1.

Refraction. Concerning the index of refraction, or nD, of turpentine oils only a few reliable data are available. At 15° the index of refraction is about 1,470. According to Coste1), the correction for every degree centigrade is 0,00037. Old, hence modified, turpentine oils have a higher refraction capacity than freshly distilled ones.

Abnormal refraction indicates adulteration: pine tar oil increases the refractive index, petroleum hydrocarbons lower it. The presence of the latter is verified by determining the index of refraction of the several fractions. Compare p. 46.

Solubility. In absolute alcohol turpentine oil is soluble in all proportions, but rather difficultly in dilute alcohol. In many instances this property makes relatively easy its detection as adulterant. However, the solubility of turpentine oil in alcohol undergoes decided changes upon aging. Whereas the solubility of most volatile oils diminishes with age, the case is reversed with turpentine oil2). In order to obtain a clear solution, more alcohol is required for freshly distilled or rectified turpentine oil, than for an old oil which has been in contact with the air for a long period. The explanation for this observation is based on the formation of oxygenated compounds which are more readily soluble.

1) Analyst 33 (1908), 209 to 230; Chem. Zentralbl. 1908, II. 731.

2) A normal American turpentine oil originally required 6 parts of 90 p. c. alcohol to effect solution. After standing seven weeks, only 3 parts were required to produce a clear solution. French oil, which had been standing 4 years in a flask not completely filled, was soluble to a clear solution in 1 part of 80 p. c. alcohol. Compare also the statements on p. 26, footnote 1.

Solubility of several turpentine oils in alcohol of various percentage strength, according to Ledermann and Godeffroy1).

Strength of alcohol expressed in percentage by volume

Kind of terpentine oil

d15o

70

80

85

90

95

The following number of parts are required

1. French, crude ....

0,861

66

18

14

7

2

2. French, rect......

0,860

80

17

12

6,7-7

2 - 2,4

3. American, crude . . .

0,862

56

20

12

5

2

4. American, rect.....

0,862

60 - 64

17 - 19

12 - 14

5-6

2,2

5. Austrian, crude ....

0,865

-

-

-

6

-

6. Austrian, rect.....

0,862

13

8

3

7. Polish (Kienol) ....

0,866

___

___

5

8. Russian (Kienol) . . .. .

0,860

49

16

11

5,6

2

Because of this changeability, little reliance can be placed on solubility as a test for purity. As a rule, good turpentine oil is soluble to a clear solution in 5 to 8 parts of 90 p. c. alcohol.

As to the relative solubility of turpentine oil and alcohol, this subject has been investigated by M. Vezes2) together with M. Mouline and R. Bredon. They determined the ratio of solubility of a large number of mixtures of turpentine oil and dilute alcohol of varying percentage strength. The results have been tabulated and represented graphically by curves. Turpentine oil and absolute alcohol are miscible in all proportions and do not separate when the temperature of the mixture is greatly decreased. However, the temperature of solutions of turpentine oil and dilute alcohol cannot be lowered ad libitum without bringing about separation. The temperature of separation depends on the strength of the alcohol, the ratio between alcohol and turpentine oil, and upon the pressure to which the mixture is subjected. In these experiments the pressure was always the normal atmospheric pressure, hence negligible.

1) Zeitschr. d. allg. osterr. Apoth. Ver. 15 (1876), 381; Jahresber. f. d. Pharm. 1877, 394.

2) Bull. Soc. chim. III. 31 (1904), 1043. - Proces-verbaux des seances de la Societe des Sciences physiques et naturelles de Bordeaux (seances du 16 juin 1904, du 28 juin 1906, du 13 juin et du 24 octobre 1907); Report of Schimmel & Co., April 1905, 77; April 1907, 99; April 1908, 104.

If a complete separation of the components of the turpentine oil-alcohol mixture is to be effected by means of water, sufficient water should be added to reduce the alcohol to 18,4 per cent, by volume. The upper layer then consists of pure oil, and the lower or aqueous-alcoholic layer contains only traces of oil, hence the separation may be regarded as complete.

Turpentine oil is soluble in all proportions in ether, chloroform, carbon disulphide, benzene, petroleum ether, aniline (compare also p. 34), glacial acetic acid') (compare also p. 33), and the fatty oils. The ratio of solubility of turpentine oil and dimethyl sulphate has been studied by M. Dubroca2), that of turpentine oil and aniline by Queysanne3), also by Louise4).

When turpentine oil is mixed with other volatile oils, turbidity occasionally is observed (compare vol. I, footnote 2 on p. 567). Oil of turpentine is itself an excellent solvent for fats, resins and most varieties of caoutchouc.

Boiling Temperature. Turpentine oil begins to boil somewhat below 155°. By far the largest part, namely 75 to 80 p. c, boils between 155 and 162°. Above 162° the thermometer rises rapidly and finally there remains in the flask a viscid, resinous mass the odor of which resembles that of colophony. According to Vezes5), the requirements as to the boiling temperature of turpentine oil can be formulated in the following manner: Turpen1) The mixture of equal volumes of glacial acetic acid and turpentine oil remains clear at 14,5 to 16,5°, provided the glacial acetic acid is 99,5 p.c. strong. The mixture is turbid or separates into two layers if the glacial acetic acid is 98,9 p. c. strong or weaker. P. W. Squire and C. M. Caines, Pharmaceutical Journ. 68 (1902), 512. tine oil begins to boil between 152 and 156° (760 mm). At least 80 per cent, by weight should distill over below 16401). So far as rectified American turpentine oil is concerned, detailed reports as to the amounts that distil over in the several fractions, also as to the optical rotation and the specific gravities of these fractions have been made by Kremers2).

1) Journ. de Chim. phys. 5 (1907), 463; Report of Schimmel & Co. April 1908, 104.

3) Sur la solubilite r6ciproque de pessence de te're'benthine et de paniline. Bordeaux 1909.

4) Compt. rend. 150 (1910), 526. Comp. also Vezes, ibidem 698; P. E. Gallon, Sur la solubilite reciproque de pessence de terebenthine dextrogyre et de Vaniline. Bordeaux 1911.

5) Sur la definition de pessence de te're'benthine commercialement pure. Bordeaux 1910, p. 7.