DETECTION OF PETROLEUM AND MINERAL OIL

2. DETECTION OF PETROLEUM AND MINERAL OIL

a. Oleum Test. 

The saturated paraffinic hydrocarbons, found in petroleum oils, are chemically very inert ; they are not destroyed by fuming sulfuric acid. Other compounds are attacked, giving rise to reaction products which are soluble in sulfuric acid.

Procedure:¹⁷⁸ Place 20 cc. of fuming sulfuric acid in a dry cassia flask¹⁷⁹ of 150 cc. capacity, and cool thoroughly in an icesalt mixture. Add slowly 5 cc. of the oil in question from a small burette. The oil should be added drop by drop, with frequent shaking and cooling in the ice-salt mixture, since too rapid addition of the oil is apt to cause the liberated sulfur dioxide to carry part of the acid and oil out of the flask. After the oil has been added, the flask is again shaken and permitted to stand at room temperature for 10 min. It is then warmed on a steam bath for 5 min. with frequent agitation. The flask is permitted to cool to room temperature and is then filled with 95% sulfuric acid. After standing overnight, the mineral oil will rise into the neck and separate as a colorless, or strawcolored liquid. As a confirmatory test, a small amount of the separated mineral oil may be removed from the cassia flask (by means of capillary action, using a glass tube drawn out to a small tip). The refractive index of this separated oil should be less than 1.4400.

A flavor test often will prove of value for the detection of kerosene. In this connection, see the discussion of adulteration of "Orange Oils of French Guinea” Vol. III.

Since petroleum fractions often contain aromatic and unsaturated compounds as well as paraffins, the separation of the paraffinic portion described above does not usually represent the total amount of added petroleum. In general, such actual separation usually is a small percentage of the adulterant.

The test may be rendered more sensitive by preliminary fractionation of the oil.

The addition of petroleum fractions to an oil causes a lowering of the specific gravity, index and optical rotation. The solubility of the oil usually is affected : this is the basis of the well-known Schimmel Test for citronella oils described below.

b. Schimmel Tests.

The "Old Schimmel Test."¹⁸⁰ In order to limit the amount of adulteration of citronella oils with petroleum fractions, the chemists of Schimmel and Company introduced the well-known Schimmei Test. Several modifiations of this test have been proposed, but the trade accepts the following itrocedure in writing contracts for oils.

Procedure: Into a glass-stoppered, graduated cylinder introduce exactly 1 cc. of the oil. Add dropwise 80% alcohol until a clear solution results. This should occur at 1 to 2 volumes. Add sufficient 80% alcohol to bring the amount of added alcohol to 10 volumes. The solution may show a slight opalescence, but should not separate oily droplets even after standing for several hours. When adding the alcohol, violent shaking should be avoided to prevent an emulsion that will separate only after very prolonged standing.

A citronella oil meets the Schimmei Test if it yields a clear solution in to 2 volumes of 80 per cent alcohol and does not separate oily droplets when the amount of alcohol added is increased to 10 volumes. This test limits the amount of added petroleum fractions to about 10 per cent. If more than his amount has been added, oily droplets will form on the surface of the alcoholic solution. Additions of fatty oils will result in the formation of oily droplets which settle to the bottom.

“The "New Schimmei Test."¹⁸¹ At a later date the description of the original test was modified resulting in the so-called "New Schimmei Test." This test is somewhat more stringent than the "Old Schimmei Test" deicribed above. However, the trade has not accepted the new version. A description of this test follows:

Oil of oitronella Ceylon must be clearly soluble in from 1 to 2 volumes of X0% alcohol by volume at 20. Upon the further addition of alcohol of the same strength, the solution should show an opalescence at the most, but no turbidity or direct cloudiness. The alcohol must be added slowly, drop by drop; the addition being at once interrupted if a cloudiness or turbidity appears. The alcohol is then added slowly, drop by drop, until the point of highest or maximum cloudiness or turbidity is obtained. The mixture is carefully set aside and maintained at 20 to observe if any oily constituents separate out. Ten volumes of 80% alcohol at the most are added. If oil separates out immediately or after prolonged standing, the oil does not pass the "New Schimmei Test." Strong or violent shaking must be avoided since any possible oily separation will become finely dispersed and will not separate out on standing.

Many oils will show an oily separation at the point of highest cloudiness or turbidity, but will show no oily separation if 10 volumes of 80 per cent alcohol are added.

The "Raised Schimmel Test"182 In order to limit adulteration with mineral spirits to 5 per cent, the "Raised Schimmel Test" was introduced. This test has never attained commercial importance.

Oil of citronella Ceylon is mixed with 5% of kerosene and the "Old Schimmel Test" is applied, disregarding any intermediate stages of cloudiness or turbidity; i.e., simply add 80% alcohol up to 10 volumes. A fresh unadulterated citronella oil will show no oily separation. Oils containing small amounts of petroleum will show an oily separation either immediately or after prolonged standing at 20⁰.

This test is by far the most stringent of the three.

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178 This procedure is essentially the Oleum Test of "The National Formulary," Eighth Edition, 643 (Turpentine Oil).

179 A narrow necked Babcock bottle may be used in place of the cassia flask; this offers the further advantage of permitting the bottle and contents to be centrifuged for better separation.

180 Ber. Schimmel & Co., October (1889), 22; (1917), 14.

181 Ber. Schimmei & Co. (1923), 18.