Sulphuric Acid Method. It may be pointed out in advance that the differences of opinion regarding this method are as great as those concerning the nitric acid method. The idea to utilize the stability of the petroleum hydrocarbons toward strong sulphuric acid in order to detect their presence in turpentine oil, dates back to Armstrong2). Herzfeld3) improved the method by supplementing the treatment of concentrated sulphuric acid with a second treatment with fuming sulphuric acid. Eibner and Hue4) attribute the varying results obtained by analysts5) when treating turpentine oil with sulphuric acid to the different strength of the fuming sulphuric acid employed and to variations in the conditions observed. The fuming sulphuric acid of commerce varies greatly and this variation is not sufficiently recognized by analysts. Hence they determined the conditions under which comparable results can be obtained provided the apparatus employed by them is used.
1) Marcusson, Chem. Ztg. 33 (1909), 966, 978, 985; 34 (1910), 285; 36 (1912), 413, 421. - Herzfeld, ibidem 33 (1909), 1081; 34 (1910), 885.
2) Journ. Soc. chem. Industry 1 (1882), 478; Chem. Zentralbl. 1883, 206.
3) Zeitschr. f. off. Chem. 9 (1903), 454; Chem. Zentralbl. 1904, I. 548.
4) Chem. Ztg. 34 (1910), 643, 657.
5) Wilson, Zeitschr. f. angew. Chem. 1890, 371. - Bohme, Chem. Ztg. 30 (1906), 633. - Mc. Candless, Journ. Americ. chem. Soc. 26 (1904), 981; Chem. Zentralbl. 1904, II. 1074. - Marcusson, Chem. Ztg. Repert. 32 (1908), 325. - Coste, Analyst 33 (1908), 219; 34 (1909), 148; Chem. Zentralbl. 1908, II. 731;
The burette adapted to shaking (fig. 3) used by Eibner and Hue consists of a lower narrow portion of about 10 cc. capacity. 7 cc. of this part are calibrated into 1/10 cc. The wider, middle portion has a capacity of about 25 to 50 cc. It is provided with two projections of glass, by means of which the burette can be suspended from a clamp. The upper, narrow portion is likewise calibrated like the lower portion and is capped with a glass ground stopper provided with a small opening on the same side with the calibration, as illustrated in the cut. The object of the wider, middle portion is to enable a thorough mixing of the liquids. The upper calibration enables the reading off of the amount of residue six hours after the treatment with the concentrated sulphuric acid. The lower calibration enables a like reading of the amount of residue 40 to 50 minutes after the treatment with the fuming sulphuric acid.
Directions: "By means of a burette, 15 cc. of concentrated sulphuric acid sp. gr. 1,84 are transferred to the shaking burette. From a 10 cc. burette 1/2 cc. of the turpentine oil to be examined is added at a time. After each addition the stopper is inserted in such a manner that the small perforation is open. The burette is grasped about the middle, wider part and shaken thoroughly until the principle reaction ceases. The burette is then grasped about the upper portion, placed in as nearly a horizontal position as possible and shaken again so that all of the sulphuric acid comes in contact with the turpentine oil. This procedure is repeated until the 10 cc. of turpentine oil have been added. Finally the stopper is turned so as to close the perforation and the mixture is once more thoroughly shaken. According to the amount of benzin present, the time of addition of the turpentine oil will vary from 15 to 50 minutes. Concentrated sulphuric acid is then poured down the sides of the burette until the liquid has risen to about the 2 cc. mark of the upper calibration. After 6 hours the volume of the residue is read off. If this does not amount to more than 2 cc. the turpentine oil was probably pure. The polymerization products are then drawn off and, according to the volume, the residue is treated with varying amounts (see table) of fuming sulphuric acid containing 20 p. c. of anhydride. If the volume varies but little from the volumes recorded in the table, the nearest one is choosen. If the variation is greater interpolation is resorted to. 1 cc. of fuming sulphuric acid is added at a time. After each addition the stopper is placed in position so that the perforation is open. The liquid is allowed to flow into the middle portion of the burette, the lower portion is grasped with the left hand, the middle or wider portion with the right hand, the apparatus placed in as nearly a horizontal position as possible and the contents shaken thorougly.
1909, I. 1614. - Marcusson, Chem. Ztg. 33 (1909), 966, 978, 985; 34 (1910), 285. - Herzfeld, ibidem 33 (1909), 1081; 34 (1910), 885. - Nicolardot u. Clement, Bull. Soc. chim. IV. 7 (1910), 173. - Morrell, Journ. Soc. chem. Industry 29 (1910), 241. - Coste, Analyst 35 (1910), 112; Chem. Zentralbl.
1910, I. 1297.
After no more heat is produced, the burette is grasped at the upper end with the right hand and the contents are given another thorough shaking. Another cc. of acid is added going through the same procedure. After the required amount of sulphuric acid has been added the entire liquid is given a final thorough shaking and the burette suspended from a clamp. After 40 to 45 minutes the volume of the residue is read off. Pure oil yields a residue of from 0 to 3 p. c. (0 to 0,3 cc). If the residue amounts to 4 p. c, adulteration is assumed. If it is larger, the amount of the adulteration can be directly computed; cc. x 10 = p. c."
Residue after treatment with 15 cc. conc. H2So4
Quant. of fuming
H-SO* (abt. 20% SO))
Residue after treatment with 15 cc. conc. H2So4
Quant. of fuming
H2So4 (abt. 20 % So3)
P. van der Wielen1) suggests the following modification of the sulphuric acid method. To 80 cc. of sulphuric acid (d 1,698), contained in a flask of about 1 liter capacity, 20 cc. of the oil to be tested are added and the mixture set aside with frequent shaking. 300 cc. of water are added and the unchanged oil is distilled into a flask with a graduated neck. The oily distillate is dried and its index of refraction is determined, also the temperature at which its solution in aniline will separate. The refraction of the original oil should likewise be known. From these data, supplemented by the knowledge of the amount of oil that has not been polymerized by the sulphuric acid van der Wielen claims that reliable conclusions as to the addition of hydrocarbons2) can be drawn.