When it is not important to obtain all of the acid present, the process may be simplified in the following manner:

The fat acids obtained from twenty grams of oil are dissolved in 300 cubic centimeters of ether and treated at the temperature of ice-water with a quantity of the alcoholic lead acetate solution mentioned above. Lead oleate remains in solution and the precipitate which forms after a few hours consists almost wholly of the lead salts of the solid fat acids. The precipitate is collected, washed with ether and identified in the usual manner.

362. Cottonseed Oil, Bechi’s Test.—Crude, fresh cottonseed oil, when not too highly colored, and generally the refined article, may be distinguished from other oils by the property of reducing silver salts in certain conditions. The reaction was first noticed by Bechi and has been the subject of extensive discussions.[328]

The process as proposed by Bechi has been modified in many ways but apparently without improving it. It is conducted as follows: One gram of silver nitrate is dissolved in 200 cubic centimeters of ninety-eight per cent alcohol and forty cubic centimeters of ether and one drop of nitric acid added to the mixture. Ten cubic centimeters of the oil are shaken in a test tube with one cubic centimeter of this reagent, and then with ten cubic centimeters of a mixture containing 100 cubic centimeters of amyl alcohol and ten of colza oil. The mixture is divided into two portions, one of which is put aside for future comparison and the other plunged into boiling water for fifteen minutes. A deep brown or black color, due to the reduction of silver, reveals the presence of cottonseed oil.

In this laboratory the heating is accomplished in a small porcelain dish on which is often deposited a brilliant mirror of metallic silver. The white color of the porcelain also serves as a background for the observation of the coloration produced. In most instances a green color has been noticed after the reduction of the silver is practically complete. Unless cottonseed oil has been boiled or refined in some unusual way, the test, as applied above, is rarely negative. The reduction of the silver is doubtless due to some aldehydic principle, present in extremely minute quantities, and which may be removed by some methods of technical treatment. The silver nitrate test therefore is reliable when the reduction takes place, but the absence of a distinct reaction may not in all cases prove the absence of cottonseed oil.

363. Milliau’s Process.—Milliau has proposed the application of the silver salt directly to the free fat acids of the oil instead of to the oil itself.[329] About fifteen cubic centimeters of the oil are saponified with alcoholic potash in the usual manner, 150 cubic centimeters of water added to the dish and the mixture boiled until the alcohol is evaporated. The fat acids are freed by the addition of decinormal sulfuric acid and as they rise to the surface in a pasty condition are removed with a spoon. The free acids are washed with distilled water. The water is drained off and the free acids dissolved in fifteen cubic centimeters of ninety-two per cent alcohol and two cubic centimeters of a three per cent solution of silver nitrate. The test tube containing the mixture is well shaken and placed in a water-bath, out of contact with light, and left until about one-third of the alcohol is evaporated. Ten cubic centimeters of water are added, the heating continued for a few minutes and the color of the supernatant fat acids observed. The presence of cottonseed oil is revealed by the production of a lustrous precipitate which colors the fat acids black. In some cases the process of Milliau gives better results than the original method of Bechi, but this is not always the case. It does away with the use of amyl alcohol and colza oil, but its manipulation is more difficult. In all doubtful cases the analyst should apply both methods.

364. Detection of Sesame Oil.—Milliau has pointed out a characteristic reaction of this oil which may be used with advantage in cases of doubtful identity.[330] The identification is based on the fact that the free acids of sesame oil, or some concomitant thereof, give a rose-red color when brought in contact with a solution of sugar in hydrochloric acid.

The analytical process is conducted as follows: About fifteen grams of the oil are saponified with alcoholic soda and when the reaction is complete treated with 200 cubic centimeters of hot water and boiled until the alcohol is removed. The fat acids are set free with decinormal sulfuric acid and removed with a spoon as they rise to the surface in a pasty state, in which condition they are washed by shaking with water in a large test tube. When washed, the acids are placed in an oven at 105° until the greater part of the water is evaporated and the acids begin to become fluid. At this point they are treated with half their volume of hydrochloric acid saturated with finely ground sugar. On shaking the mixture, a rose color is developed which is characteristic of the sesame oil. Other oils give either no coloration or at most a yellow tint.

365. The Sulfur Chlorid Reaction.—Some vegetable oils, when treated with sulfur chlorid, give a hard product similar to elaidin, while lard does not. This reaction is therefore helpful in discriminating between some vegetable and animal glycerids. The process which is described by Warren has been used with some satisfaction in this laboratory.[331]

Five grams of the oil or fat are placed in a tared porcelain dish and treated with two cubic centimeters of carbon bisulfid and the same quantity of sulfur chlorid. The dish is placed on a steam-bath and its contents stirred until the reaction is well under way. The heating is continued until all volatile products are evaporated, the hard mass being well rubbed up to facilitate the escape of imprisoned vapors. The powdered or pasty mass is transferred to a filter and washed with carbon bisulfid to remove all unaltered oil. The washing with carbon bisulfid is hastened by pressure and about 200 cubic centimeters of the solvent should be used. After drying, the weight of insoluble matter is obtained and deducted from the total weight of the sample used.

The color and tenacity of the hard, insoluble portion are characteristic. The quantitive part of the operation appears to have but little value, but applied qualitively in this laboratory it produces hard, leathery masses with cotton, olive and peanut oils, and but little change in lard and beef fats. Qualitively applied, the process is conducted as described above but without making the weighings. In this instance it is as easy of application as the process of Bechi and is deserving of greater attention than has been given it by analysts.

In the combination which takes place between the sulfur and the fat it is probable that only addition products are formed, since the quantity of alkali required for saponification is not diminished by previously treating the fat with sulfur chlorid.[332] The reactions which take place are probably well represented by the following equations, in which oleic acid is treated with sulfur chlorid:

C₁₈H₃₄O₂ + S = C₁₈H₃₄S.O₂.  
C₁₈H₃₄S.O₂ + NaOH = C₁₈H₃₄SO₂Na + H₂O.

366. Detection of Cholesterin and Phytosterin in Glycerids.—Cholesterin is often found in animal glycerids and a corresponding body, phytosterin, is sometimes found in oils of a vegetable origin.[333] When one of these two bodies is present it may be useful in distinguishing between animal and vegetable glycerids. They are detected as follows: Fifty grams of the glycerids in each case are saponified with alcoholic alkali, preferably potash, in order to have a soft soap. After saponification is complete, the alcohol is evaporated and the residual soap dissolved in two liters of water. The mixture is shaken with ether and the ethereal solution evaporated to a small bulk. The residue, which may contain a small quantity of unsaponified fat, is again treated with alcoholic potash and subjected a second time to the action of ether, as indicated above, with the addition of a few drops of water and of alcohol if the emulsion separate slowly. The ethereal extract finally secured is allowed to evaporate slowly and the cholesterin (phytosterin) is obtained in a crystalline form. The melting point of the cholesterin crystals is 146° and that of the phytosterin 132°.

Cholesterin crystallizes in thin rhombic tables while phytosterin separates in stellar aggregates or in bundles of long needles.

When dissolved in chloroform the two products show different color reactions with sulfuric acid, cholesterin giving a cherry and phytosterin a blue-red tint. In a mixture of animal and vegetable glycerids the two products are obtained together and the melting point of the mixture may afford some idea of the relative quantities of each present. It is evident, however, that no reliable judgment can be formed from these data of the relative proportions of the two kinds of glycerids in the original sample.

367. Cholesterin and Paraffin in Ether Extracts.—In ethereal extracts of some bodies, especially of flowers of the chrysanthemum, paraffin is found combined with cholesterin. The two bodies may be separated as follows:[334]

The ether extract is treated with aqueous then with alcoholic potash several times; the residue soluble in ether is a solid body melting at from 70° to 100°.

If the ethereal solution be cooled in a mixture of snow and salt, a crystalline deposit is formed. This substance, purified by repeated precipitations, is obtained colorless in fine crystalline scales melting at 64°. It is very soluble in ether, benzene and chloroform, almost insoluble in cold alcohol, and somewhat soluble in hot.

Its percentage composition is:

It is therefore a paraffin.

The ethereal solution, freed by the above process from paraffin, leaves on evaporation a crystalline mass which is cholesterin, retaining still a small quantity of fat matters. In treating the crystals with alcoholic potash these fat bodies are saponified and the residue is taken up with ether. The cholesterin is obtained in fine needles melting at from 170° to 176°. It presents all the reactions of cholesterin, especially the characteristic reaction with chloroform and sulfuric acid.

368. Absorption of Oxygen.—Among oils a distinction is made between those which oxidize readily and those which are of a more stable composition. Linseed oil, for instance, in presence of certain metallic oxids, absorbs oxygen readily and is a type of the drying oils, while olive oil represents the opposite type.

The method of determining the quantity of oxygen absorbed is due to Livache and is carried out as follows:[335]

Precipitated metallic lead (by zinc) is mixed in a flat dish, with the oil to be tested, in the proportions of one gram of lead to three-quarters of a gram of oil, and exposed to the air and light of the workroom. The dish is weighed from time to time until there is no longer any increase in weight.

Instead of lead, finely divided copper has been used by Krug in this laboratory, but the percentage of absorption of oxygen is not so high with copper as with lead. Krug found the quantities of oxygen absorbed, after nine days, by the samples treated with copper and lead respectively to be the following:

Livache found that linseed oil absorbed about twice as much oxygen as indicated by the data just given.

369. Elaidin Reactions.—In discriminating between oils and fats having a preponderance of olein and others with a smaller proportion of that glycerid, the conversion of the olein into its isomer elaidin is of diagnostic value. The following will be found a convenient method of applying this test:[336]

About ten cubic centimeters of the oil are placed in a test tube together with half that quantity of nitric acid and one gram of mercury. The mixture is shaken until the mercury dissolves when the mass is allowed to remain at rest for twenty minutes. At the end of this time it is again shaken and placed aside. In from one to three hours the reaction is complete. Olive, peanut and lard oils give very hard elaidins. The depth to which a plunger of given weight and dimensions sinks into an elaidin mixture at a given temperature, has been used as a measure of the percentage of olein contained in the sample of oil, but it is evident that such a determination is only roughly approximate. Copper may be used instead of mercury for the generation of the oxids of nitrogen, but it is not so effective. The vapors of nitric oxids may also be conducted directly into the oil from a convenient generator. The reaction may also be accomplished by shaking the oil with nitric acid and adding, a drop at a time, a solution of potassium nitrite.

AUTHORITIES CITED IN PART FOURTH.