Page:The American Cyclopædia (1879) Volume II.djvu/726

 706 BLEACHING BLEACHING POWDER minous, and oily bodies present in the manu- factured goods, are by this method resolved in- to soluble compounds and removed ; and when in 1837 the process as practised became known to the scientific bleachers and printers of Miihl- hausen, it drew forth their expressions of ad- miration for its completeness. This method is founded on the two following principles : 1. The conversion of the fatty and waxy matters into soaps ; and for security and economy, it is preferable that these soaps should have alkali- no-earthy bases ; caustic lime becomes, there- fore, a most effectual agent. 2. The decompo- sition of the basic soaps formed, so as to con- vert them into soluble soaps, which is effected by the action of an alkaline carbonate. These are the cardinal principles on which this almost perfect process is founded, but there are prac- tical points of interest. After the principles were published, M. Auguste Scheurer of Muhl- hausen suggested the passing of the goods from the lime into diluted acid. This step, by no means essential, increases the certainty of an easy decomposition of the lime soap, as the acid seizing the base enters into combination with it, leaving the fatty acid free to combine with the base of the alkaline carbonate, and form soluble soap. In describing the process as almost perfect, a point was in view which called for this qualifying phrase. Dr. Dana found that after the new process had been ap- plied, and modified applications had been made, there still remained adhering to the fibre a sub- stance which has many of the characters of wax. This substance he studied at great length, separating it from bleached cotton by means of boiling alcohol, which deposits it on cooling. Its few affinities do not allow of the application of any special agent for removing it wholly ; while the solution of rosin in alkali, combining with it, dissolves a portion. This body, unlike wax in its relation to coloring matter, becomes tinted in ordinary madder printing at the points where it is desirable that white ground only should appear, and no modi- fication of bleaching methods has yet met or overcome this difficulty. The steps of the pro- cess are as follows : 1. Steep the cloth in wa- ter at a temperature of about 90 F. for 24 hours. 2. Pass through a bath of milky caus- tic lime, containing 60 Ibs. for 2,500 Ibs. of cloth. 3. Boil the cloth as it passes from the second operation six hours, counting from the moment ebullition actually occurs, under a pressure of 40 to 50 Ibs. to the square inch. 4. Wash through the washing machine. 5. Pass through a bath of sulphuric acid, diluted till it marks 2 B. 6. Wash in machine. 7. Boil six hours, under a pressure of 40 to 50 Ibs. to the square inch, in a solution of carbonate of soda, containing 100 Ibs. for 2,500 Ibs. of cloth, and in which 40 Ibs. of common rosin have been previously dissolved. 8. Wash in machine. 9. Pass in washing machine through a clear solution of chloride of lime, marking 1 B. 10. Expose the cloth, as it is folded from the machine into pits with open sides, to the ac- tion of the air and carbonic acid, still satu- rated with the solution of chloride of lime. 11. Pass in washing machine through sulphu- ric acid and diluted to 2 B. 12 and 13. Wash twice in machine. The boiling is done in Bar- low's kiers, which are especially adapted to this process, which has come to be regarded both in this country and Europe as the sim- plest and best in use. ULEAUII.VG POWDER. By the action of chlorine gas upon hydrate of lime, a compound is produced which is known by the common name of chloride of lime. By the calico printers, and others who make use of it for its bleaching properties, it is called bleaching powder. It is also known as bypochlorite of lime, chlorinated lime, &c. The compound was first prepared by Mr. Tennant of Glasgow, in experimenting upon the best applications of chlorine to bleaching purposes. He first made it in the form of the saturated liquid solution ; and in 1799 he took out a patent for impregnat- ing dry quickline with chlorine. By the sug- gestion of one of his partners, slacked lime, or the hydrate, was substituted for the quicklime, having the property of absorbing large quan- tities of the gas, which the quicklime has not. In preparing it, a pure quality of lime is re- quired, free from iron, clay, and magnesia, the presence of which would seriously affect the bleaching process. It should also be well and freshly burned, and freed from all carbonic acid. Enough water is then to be added to it to cause it to fall into a fine white powder, which is the hydrate of lime. Chlorine is prepared by several different processes. One of these, still common, though becoming superseded by other methods and by modifications, consists in decomposing hydrochloric acid by heating it in contact with coarsely pulverized black oxide of manganese. This substance furnishes a large amount of oxygen gas, which in mutual decomposition unites with the hydrogen of the hydrochloric acid to form water, setting free the chlorine, an atom of which takes the place of the oxygen, forming chloride of manganese, and another atom escapes. These changes are represented by the following formula, the first part of the equation being the materials em- ployed, and the second the products obtained : 4HCl + Mn 2 O s =2H 2 q + 2MnCl + 2Cl. Another process consists in mixing the manganese ox- ide with common salt and adding sulphuric acid. The changes which are then effected are represented as follows: 2XaCl + 2II 2 S- O,+ Mn 2 0.,= Na 2 SO,+ Mn 2 S0 4 + 2H 2 O + 2C1. It is important that the manganese ore should be of the purest quality, in order to obtain from it the largest quantity of oxygen gas. Black oxide of manganese when pure gives up at a white heat 33'1 per cent, of its weight of oxygen, and passes into the red oxide. Chlo- rine gas is thus prepared in large alembics or stills, which are made of cast iron, where ex- posed to strong heat, and in part of strong