The zinc iodide-starch test solution is prepared by triturating 4 to 5 g. of starch with a little water to a milky liquid and adding this mixture in small amounts and while stirring to a boiling solution of 20 g. of pure zinc chloride in 100 cc. of water. The boiling is continued with the replacement of water lost by evaporation, until the starch is dissolved as completely as possible and the liquid has become clear. The solution is then diluted with water, 2 g. of pure, dry zinc iodide are added, the dilution completed to 1 liter and the solution filtered. Stored away in the dark, in well stoppered bottles, the clear solution can be kept. Previous to the test, one part of this solution is diluted with ten volumes of water. Of this diluted solution 3 to 4 cc. are transferred to test tubes in which the tests for bromine are made as indicated above.
1) See p. 36.
Detection Of Petroleum. Ordinary kerosene as well as lighter and heavier fractions of petroleum are used for the adulteration of turpentine oil. The lower petroleum products are recognized by the lowering of the specific gravity, also by the depression of the inflammability test1). The heavier petroleum products are not volatile with water vapors. Hence, when turpentine oil is rectified with water vapor they remain behind as a fluorescing residue that is not acted upon by concentrated nitric acid and sulphuric acids.
The following fractions of American petroleum are mentioned by ). H. Long2) as suitable for adulteration. With their specific gravities they are here enumerated.
Gasolin...... d15o 0,6508
Gasolin...... „ 0,7001
Benzin....... „ 0,7306
Standard White. ... „ 0,7999
Water White .... „ 0,7918 with petroleum, however, it does not. For the complete solution of turpentine oil-petroleum mixtures the following amounts of this acetic acid are required (99+1): Head Light..... „ 0,7952
Mineral Seal..... „ 0,8293
Paraffin Oil..... „ 0,8906
As so-called patent turpentine oils, a number of products have made their appearance under a variety of fanciful names. They are mostly mixtures of petroleum with turpentine oil or camphor oil, or consist entirely of petroleum hydrocarbons. Some of the names applied to these products are3) "Canadian turpentine oil, patent turpentine, turpentyne, turpenteen, larixolin, paint oil."
According to Dunwody4) mixtures of turpentine oil and petroleum can be distinguished from pure turpentine oil by their solubility in 99 per cent. acetic acid (Comp. p. 18). Absolute acetic acid (99,5 to 100 p. c.) is miscible in all proportions with both petroleum and turpentine oil. An acetic acid made by adding 1 cc. of water to 99 cc. glacial acetic acid yields a clear solution with turpentine oil when mixed in the proportion of 1:1;
1) Comp. p. 21.
2) Journ. anal. and appl. Chemistry 6, No. 1; Journ. Parfum. et Savonn. 24 (1911), 112.
3) Pharm. Zentralh. 33 (1892), 131.
4) Americ. Journ. Pharm. 62 (1890), 288.
Require for solution in acetic acid (99+1)
Conradson1) detects the presence of petroleum in turpentine oil according to the following method: On a water bath 50 cc. of oil are evaporated to 1 to 2 cc. If the oil is free from petroleum, the residue dissolves to form a clear solution in 5 to 10 cc. of glacial acetic acid. If 10 p. c. or more of petroleum are present, the mixture is turbid and upon standing separates into two layers.
Formerly the Prussian Customs Authorities directed the use of the different solubility of turpentine oil and mineral oils in aniline (comp. p. 18) as a means to detect patent turpentine oils.
"To a measuring cylinder of 50 cc. capacity which is calibrated into cubic centimeters and which is provided with a glass stopper, 10 cc. of oil are transferred and then 10 cc. of aniline. The cylinder is then stoppered and thoroughly shaken. If after five minutes the liquid no longer appears uniform but reveals two layers, patent turpentine oil is present."
For the quantitative determination of petroleum in turpentine oil H. C. Frey2) uses somewhat different proportions. He recommends that 10 cc. of the oil be shaken with 30 cc. of aniline in a graduated tube for five minutes and that the mixture be then set aside. If petroleum be present it rises to the surface as a separate layer so that the amount can be read off. Care should be taken to have the aniline perfectly anhydrous. In order to test the utility of the method which, according to Frey, gives excellent results, Schimmel & Co.3) have tested turpentine oil to which varying amounts of petroleum had been added. With the above method the following results were obtained: 1) Journ. Soc. chem. Industry 16 (1897), 519; Chem. Zentralbl. 1897, II. 449. 2) Journ. Americ. chem. Soc. 30 (1908), 420. 3) Report of Schimmel & Co. October 1908, 123.
Amount of oil separated cc. %
Turpentine oil + 5 % petroleum
+ 10 %
+ 15 %
+ 20 %
+ 30 %
+ 50 %
The reading should be postponed for at least 24 hrs. since a turpentine oil to which petroleum up to 15 p. c. has been added yields, first of all, a clear solution. Later on this becomes turbid and the petroleum separates gradually. From the above table it becomes apparent that a petroleum content up to 5 p. c. cannot be detected according to Frey's method. A petroleum content between 5 and 10 p. c. is revealed but not in its entirety. In isolated cases even an oil to which 15 p. c. of petroleum had been added remained clear permanently so that even in such an instance the method was not reliable. Again, results that are too high are found when the petroleum content is greater, for then the aniline does not dissolve out all of the turpentine oil from its mixture with petroleum. Moreover, if as much as 15 p. c. be present, the adulteration is indicated by the specific gravity of the mixture, which for turpentine oil should not be below 0,864. These results scarcely render applicable the attribute "excellent" as applied to Frey's method. Nevertheless the method may prove useful provided the amount of petroleum added is not too small1).