(5) Estimation of the Oleic, Stearic, and Palmitic Acids.—To do this, advantage is taken of the solu bility of oleate of lead in ether, so enabling its separation from the stearate or palmitate of the same metal. As formerly conducted, this was a tedious and not over accurate process ; but by the apparatus and process devised by Dr. Muter, the estimation is rendered simple. Three cases pre sent themselves, as follows :— (a) For the Oleic Acid in non-drying Oils and Fats.—A small quantity (not more than 1.5 grm.) of the purified fat is saponified by alcoholio potash in a flask, washed into a basin with boiling distilled water, and the alcohol is removed by evaporation, all as described before in the estimation of the total fatty acids. The solution is kept boiling, and treated with acetic acid, drop by drop, until a decided permanent turbidity is produced ; dilute solution of caustic potash is then added by drops, with constant stirring, until the liquid just clears again.
The clear solution is then precipitated by plumbic acetate in slight excess, and stirred until the precipitated soap settlea thoroughly. The supernatant liquor is poured off, and the soap is at once washed by boiling with a large volume of distilled water, and decanting. By this process, are obtained the perfectly neutral lead salts, containing :—Plumbic oleate plumbic palmitate and plumbio stearate The first is readily soluble in ether ; the two last are quite insoluble. The soap is scraped from the basin with a platinum spatula, and transferred to a flask of 100 c.c.
capacity. The basin ie rinsed into the flask with absolute ether, and then the flask is filled up with the same solvent, corked, shaken at intervals for some hours, and finally set to subside. The whole is then filtered through white blotting paper, and the precipitate is washed with ether, till the wash ings cease to blacken with ammonium hydrosnlphide. The filtrate and washings (which should not exceed 200 c.c.) contain the plumbic oleate, while the palmitate and stearate remain on the filter. Having thus got a solution of pure neutral oleate of lead in ether, it is transferred to a long tube of 250 c.c., graduated from the bottom upwards, furnished with a well ground stopper, and having a stopcock placed at 50 c.c. from the bottom (Fig. 1045). About 20 c.c. of a mixture of one part hydrochloric acid and two parts water are then added ; the tube is stoppered, well shaken, and set to subside, when a clear solution of oleic acid remains, the plumbic chloride sink ing to the bottom. When sufficiently settled, a fixed portion of the ethereous solution is run off through the stopcock into a tared platinum dish, evaporated at a gentle heat, then dried at 100° (212° F.), and the oleic acid is weighed and calculated to the whole bulk. To make sure, it is well to run off two different quantities, and weigh them, so checking one by the other.
(13) For the Oleic Acid in drying Oils.—The process is conducted in a precisely similar manner up
to the point where the whole has settled in the tube. A definite portion of the ethereous liquid is then run into a perfectly dry wide-mouthed flask of about 6 oz. capacity, carefully tared on the balance. The flask (Fig. 1047) is then fitted with a cork a, through which pass two tubes, one going down nearly to the surface of the liquid, and the other just passing through the cork. To the long tube, are attached two U -tubes o, filled with freshly-ignited chloride of calcium ; to that again, is joined a gas-bottle b, in which a steady stream of hydrogen is generated from zinc and dilute sulphuric acid. When the air has been expelled from the flask by the stream of dry hydrogen, a basin is placed under it, and warm water is poured into the basin, so as to cause the ether to evaporate. When the ether is nearly gone, the water in the basin is kept boiling till the ether is entirely evaporated (i. e., till no more smell of ether is observable at the mouth of the exit-tube). The basin is then removed, and the flask is allowed to cool (still keeping up the stream of hydrogen); when cold, it is detached and weighed, and, the tare being deducted, the weight of oleic acid is calculated to percentage.
(7) For the Stearic and Palmitin Adds.—The residue left on the filter, after extraction with ether, is carefully scraped off, and heated for some time (with constant stirring), which will liberate ti* acids, so that they will, on cooling, form a cake ; this is washed, dried, and weighed, as described in section (4). The filter-paper is also to be burned in a weighed porcelain crucible, and the ash treated with a drop or two of sulphuric acid, and again ignited. After cooling, the crucible is weighed, and, the tare being deducted, leaves the equation—as 303: 568 : : the weight of the residue ; the answer, added to the weight of the cake already found, gives the total solid fatty acids (stearic and palmitic), which is then calculated to percentage. If it be desired to find the approxi mate proportion of each of these acids, the process is as follows. Several glass tubes are drawn out at one end to a long thin point, as in Fig. 1046 (natural size). The cake of mixed acids is then melted, and a little is sucked up into a pair of such tubes, until the drawn-out parts are entirely filled, and both are allowed to cool. They are then suspended side by side with a delicate thermo meter, in a small beaker filled with water, taking care that the thermometer has a long narrow bulb placed exactly between the two tubes. Heat is now applied to the beaker, and at the moment that the fat in the thin tubes becomes transparent, the degree of heat is read off. The whole is allowed to coal gradually, and the temperature is again read at the moment of resolidification. By refer ring to the following tables, an approximate result is obtained.