1) Chem. Ztg. 29 (1905), 807. 2) Ibidem 31 (1907), 1145.
Marcusson1) recommends the above reaction as serviceable.
According to Grimaldi2), Halphen's reaction can likewise be applied to the fractions of a questionable oil. It produces a yellowish-green color when bromine vapors are passed into a solution of the rosin essence in carbon tetrachloride in the presence of phenol. The fractionation is modified so as to collect at first six fractions of 1 cc. each (as above) and then fractions of 5° each. Fractions obtained from pinolin-containing oils show a coloration that varies between lemon yellow and an intense yellow which, after a few minutes changes to malachite green. The color is very intense and is produced with a single drop of oil. The presence of alcohol or water does not interfere with the reaction. With turpentine oil the reagent produces no coloration, with pine tar oil, rosin oil, camphor oil etc. a color intermediate between red and violet.
Grimaldi carries out the test in the following manner: Into a white porcelain dish, 4 cm. in diameter, there are placed a drop of the substance to be examined and 2 cc. of a mixture consisting of 1 cc. of molten, crystallized phenol and 2 cc. of carbon tetrachloride. By means of a special apparatus, provided with a rubber bulb and containing a solution of 3 cc. of bromine in 12 cc. of carbon tetrachloride, bromine vapors are spread above the dish. The uniform distribution of the bromine vapors is accomplished by means of a funnel-like attachment blown on to the spray and fitting closely to the rim of the dish. The action of the vapors is continued until a yellow coloration (ranging between lemon yellow and an Intense yellow) is observeable along the sides of the capsule and on the surface of the liquid. Rosin essence of the boiling temperature of 170° yields a yellow color which soon changes to malachite green. The time necessary for the appearance of the color varies according to the rosin essence content of the oil under examination. If the reaction is but faint, a larger amount of oil is needed as in the previous test. Fractions of 20 cc. are first collected and these are then refractionated into fractions of 1 cc. each.
1) Chem. Ztg. 33 (1909), 966.
2) Ibidem 31 (1907), 1145; 34 (1910), 721.
As already pointed out under "Acid Content" on p. 22, traces of rosin oil almost invariably distill over with the turpentine oil. With the more primitive methods of distillation this cannot be avoided, hence a moderate rosin essence content must be tolerated.
According to Vezes1), the presence of abnormal amounts of rosin oil can be detected refractometrically by testing the five equal fractions into which the turpentine oil has been resolved. This method likewise throws light on the presence of direct adulterants ("adulterants anormaux"), such as petroleum hydrocarbons, carbon disulphide, etc.
Test: 250 cc. of turpentine oil are resolved, by means of fractional distillation, into five parts of 50 cc. each, four of which are distillates, the residue constituting the fifth. Assuming that the boiling points of the adulterants vary from that of the turpentine oil, the middle fraction 3 may be regarded as pure turpentine oil and the adulterants looked for in the extreme fractions. Under like physical conditions the indices of refraction n1 n3 and n5 of fractions 1, 3 and 5 respectively are determined. From the differences of the values found, viz. n3 - n1 = 6 and n5 - n3 = a, conclusions are drawn as to the purity of the oil. A systematic study of d and A for mixtures of rectified turpentine oil with practically possible adulterants has established the fact that in the presence of exclusively normal impurities d remains almost unchanged. (For rectified turpentine oil 0,0000 <<S< 0,0010). However, with the increase of the percentage of added substances, A increases. This increase corresponds to the formula A = 0,0032 + 0,0037. X (X = p. c. rosin oil + colophony). The determination of the acid value A enables the computation of the percentage of colophony C according to the equation C = A/17, hence the difference X - C will yield the percentage of rosin oil. The addition of adulterant brings about a lowering of the boiling point and causes appreciable differences in the values for d and A. Pure turpentine oil should reveal the following values. d should vary between 0,0000 and 0,0010, A <C0,0125 (corresponding to 2,5 p. c. of normal impurities), A<1,51).
1) Bull. Soc. chim. III. 29 (1903), 896.
Detection of Pine Tar Oil. The proof for the admixture of pine tar oil in turpentine oil is commonly afforded by demonstrating the presence of the byproducts of destructive distillation by means of color reactions. However, such a method yields no results if the malodorous byproducts have been carefully removed by means of chemicals. A considerable number of patents2) have been awarded to such processes. The detection of an adulteration with pine tar oil is possible only when the physical properties of the mixture have been greatly modified or if its chemical composition (comp. pine tar oils p. 102) differs materially from that of turpentine oil.
Inasmuch as higher boiling terpenes predominate in pine tar oils the addition of such an oil increases the boiling temperature of the adulterated turpentine oil. The specific gravity is but slightly increased by the addition of pine tar oil. The index of refraction is also slightly increased. The optical rotation affords no clue.
1) In the paper referred to in footnote 1, p. 46 the statement occurs that A<1,0. The permissible acid content A was later increased by Vezes (Sur la definition de /'essence de te're'benthine commercialement pur. Bordeaux 1910, p. 9) to 1,5.
2) The treatment of pine tar oil, with alkali and subsequently with acid, formerly in vogue, does not suffice completely to remove the undesirable constituents. According to the following patents, the oils thus treated are subsequently treated in a variety of ways: Ger. Pat. 170 543 (Kaas), Treatment with alcoholic potassa and then with sulphuric acid. - Ger.Pat. 170542 (Heber), Action of permanganate solution. - Ger.Pat. 180 499 (A.Hesse), Distillation over alkali or alkali earth metals. - Ger. Pat. 202 254 (Pellnitz), Treatment with ozonized air after the addition of acids, distillation with lime. - Ger. Pat. 204 392 (Ahlers), Action of zinc dust. - Ger. Pat. 239 546 and supplemental patents (Schindelmeiser), Heating with ammonia, with or without cyanides.