VOL. fi, No 3
THE CHEMISTRY STUDENT
535
and in which oxidation of some substance in solution takes place a t one pole and reduction of some other substance in solution takes place at the other pole. Almost any oxidation-reduction reaction can be carried on by placing a solution of the reducing agent in one vessel and a solution of the oxidizing agent in another vessel and permitting a current to flow by connecting the vessels by means of a salt bridge and a pair of connected electrodes. For this reason, partial equations such as those which we have just employed are sometimes called pole reaction equations. One partial equation describes the action taking place a t the oxidizing pole; the other describes the reaction taking place at the reducing pole. It is evident that any distinction between so-called oxidation-reduction cells and cells of the Daniel1 type is artificial and based upon convention rather than upon the fundamental characteristics of the respective systems.
Solvent Extraction of Oil from Seeds. Although the process of solvent extraction has been known and in use far very many years, it is comparatively recently that its extended use has been developed in the vegetable oil industry, as an alternative to the expression of the oil from seeds by hydraulic pressure. All classes of oil seeds can he treated effectively by the solvent process, and both the oil and the residue can he guaranteed entirely free from any trace of the solvents used. Rose Downs and Thompson, Ltd., of Hull, well known as makers of solvent extraction plant, have sent us a pamphlet dealing with the subject in which i t is pointed out that the primary advantage offered by the solvent process is that, instead of leaving from 5 t o 10 per cent of oil in the residue, practically the whole of the oil can he removed from the seed. The per cent, and although i t is possible residue from the solvent process is as little as to extract all the oil, this latter procedure is not usually commercially economic. The theory of solvent extraction is that when ground oleaginous seed is saturated with some suitable chemical solvent, the oil is dissolved by the solvent and can be drained off with it. The mixture is subjected t o heat to evaporate the solvent, the vapor of which is condensed and used again. Benzine is the solvent chiefly employed in the vegetable oil industry. The process, briefly explained, consists of the following operations: after the preliminary preparation of the seed, the solvent is allowed t o percolate the ground seed in an enclosed pan. The mixture of oil and solvent is drained into an evaporator, and the solvent driven off by heat, passing as vapor to condensers, where it liquefies. The residue in the form of meal is treated with steam t o remove anyremaining solvent, which is also condensed. Rose Downs and Thompson, Ltd., have designed numerous large solvent extraction plants a t work on vegetable oils in this country, for dealing with quantities up to 1200 tons a week and are in a position to advise as t o what plant will function best in given circumstances; since it is obviously impossible to have a standard universal plant. In some instances a combination of pressing and solvent plants is employed, as, far example, to treat castor seed when a high quality medicinal oil is required. For this purpose, the medicinal oil is expressed by cold pressing in one of their "Premier" or cage type presses. The cakes from this first pressing are then broken up, and further treated in a solvent extracting plant, which extracts practically the whole of the remaining oil, less than 1 per cent usually being left in the residue.-Ckem. Age, 20, 112 (Feb. 2. 19201.
