Worstall 1) sets aside 0,1 g. of oil with 40 ccm. of Hubl's iodine solution in a glass-stoppered flask over night and then titrates back the excess of iodine. The theoretical iodine value demanded by the change of C10H10 to C10Hl6l4 is 373. The average found in the examination of 55 samples of pure turpentine oil is 384. Further investigation revealed the fact that the iodine absorption as indicated above is completed within 4 to 6 hrs. and that a large excess of iodine and prolonged action induces secondary reactions.
The iodine value of rosin spirit was found to be 185, that of rosin oil 97, of "refined wood turpentine" 212, and of "water white" 328, whereas the petroleum hydrocarbons of kerosene and naphtha add no iodine.
Hence even small additions of petroleum distillate may be detected by a reduction in the iodine value. According to Worstall, a turpentine oil with an iodine value below 370 is to be regarded as suspicious.
Mc. Gill2) corroborates Worstall's results and likewise places the lower limit for pure turpentine oil at 370.
It must be remembered, however, that comparable results are obtainable only when the conditions maintained are absolutely the same.
Thus Harvey3) who used Wijs' solution obtained iodine values ranging from 166 to 221, corresponding to the absorption of two atoms of iodine to one molecule of C10H16. According to Veitch and Donk4), genuine turpentine oil has an iodine value of 350 to 400 if Wijs' solution is employed.
A more detailed investigation, made because of the great discrepancy in the results, revealed the fact that the amount of halogen absorbed by the turpentine oil depends on the duration of the action and also on the excess of the Wijs' solution employed.
1) Journ. Soc. chem. Industry 23 (1904), 302; Chem. Zentralbl. 1904,1.1676.
2) Journ. Soc. chem. Industry 26 (1907), 847; Chem. Zentralbl. 1907, II. 1124.
3) Journ. Soc. chem. Industry 23 (1904), 413; Chem. Zentralbl. 1904, II. 265. Comp. also F. W. Richardson and E. F. Whitaker, Journ. Soc. chem. Industry 30 (1911), 115; Chem. Zentralbl. 1911, I. 1012.
4) U. S. Dept. of Agriculture, Bur. of Chemistry, Bull. Mo. 144, 1911, p. 22.
Bromine Absorption. The value of this method is denied on the one hand as it is defended on the other1). Hence a final judgement cannot be passed thereon at present.
According to Vaubel2) the bromination of turpentine oil is conducted in the following manner:
"To a solution of 1 to 2 g. of turpentine oil in chloroform, about 100 cc. of water, 5 g. of potassium bromide and 10 cc. of hydrochloric acid or the equivalent amount of sulphuric acid are added. The mixture is then titrated with a standardized potassium bromate solution until a permanent bromine reaction is produced. The end reaction can be recognized either by the coloration of the chloroform or by transferring a drop of the aqueous solution to potassium oxide-starch test paper." According to the equation C10H16 + 4 Br = C10H16Br4, 100 g. of pinene should add 254 g. of bromine. For several pure turpentine oils Vaubel ascertained bromine values of from 220 to 240. The directions issued by the German Customs Authorities for determining the bromine absorption3) are as follows:
"A mixture of 50 cc. of 98 per cent. (by weight) alcohol and 5 cc. of concentrated hydrochloric acid, sp. gr. 1,124 is introduced into a 150 cc. beaker. To this mixture 0,5 cc. of the oil to be examined are added, the amount being measured by means of a standardized pipette. The oil is completely dissolved by stirring the mixture with a glass rod. "By means of a burette of about 30 cc. capacity and calibrated into one-half cubic centimeters or less the bromine solution described below is added with constant stirring.
"At first the bromine set free by the action of the hydrochloric acid combines instantaneously with the turpentine oil. After about four-fifths of the requisite bromine solution have been added, the mixture is colored yellow. This color, however, disappears after a few seconds though it has been decidedly lemon-yellow. When, however, the disappearance of the bromine color lasts 1/2 minute, only 1/2 cc. of the solution is added at a time and the length of time required for the disappearance of the color is noted.
1) Comp. Evers, Chem. Ztg. 23 (1899), 312. - Schreiber and Zetzsche, ibidem 23 (1899), 686. - Bohme, Chem. Ztg. 30 (1906), 633. - Utz, Pharm. Zentralh. 49 (1908), 10. - Marcusson, Chem. Ztg. 33 (1909), 966, 978, 985. - Mansier, Annal. de la Chim. analyt. appl. 14 (1909), 417; Zeitschr. f. angew. Chem. 23 (1910), 46.
2) Pharm. Ztg. 51 (1906), 257.
3) 5. Nachtrag zu der Anleitung fur die Zollabfertigung. Herausgegeben vom Reichsschatzamt. Berlin 1910, p. 56.
"If the period of decoloration lasts 1 minute or more, the reaction is regarded as being ended. In some of the less pure turpentine and pine tar oils a permanent yellow color is produced before the end of the reaction has been reached. In such a case, a few drops of the liquid, removed one minute after the last addition of the bromine salt solution, are added to a diluted zinc iodine-starch test solution. (See below.) If a deep blue color is produced at once, but not otherwise, the reaction may be regarded as ended.
"If 25 cc. or more of bromine salt solution have been used, the turpentine oil is free from mineral oils. If less than 25 cc. have been used it is doubtful. In this case the sample should be examined by a chemist according to method 2 (i. e. with fuming nitric acid)1)."
The bromine salt solution required for the above test is prepared by dissolving 13,93 g. of pure potassium bromate and 50g. of potassium bromide in sufficient distilled water to make 1000cc.