BLEACHING. 



worn in this state, or as preparatory to 

 being dyed or printed, it is obvious that 

 the art of bleaching" is one of great im- 

 portance. The substances upon which 

 the bleacher is required to exercise his 

 art are, cotton, flax, hemp, wool, and silk. 

 The three former being- of vegetable 

 origin, require a somewhat similar treat- 

 ment, which in many particulars differs 

 from that which is applicable to the two 

 latter. 



The art of bleaching- consists, not mere- 

 ly in discharging- the colour of the thread, 

 but likewise in Removing- the colouring- 

 matter itself, as otherwise a sensible shade 

 would be retained. In the old method 

 this was attained by alternate exposure of 

 the thread or cloth to the action of light, 

 humidity, and atmospheric air, and to^an 

 alkaline ley, the cloth being- macerated* in 

 a solution of potash, exposed on the field 

 to the air and sun, and frequently sprin- 

 kled with water ; and these alternate 

 practices being- continued until the 

 bleaching- was complete. In the new me- 

 thod, the action of the oxymuriatic acid is 

 substituted for that of the light, air, and 

 water ; and it answers the same purpose 

 by affording oxygen to the colouring 

 niatter, thus impairing the colour, and 

 probably rendering the matter soluble 

 in the alkaline solution. 



At first this process was performed by 

 exposing the cloth to the action of the 

 pure acid in the state of gas. It was 

 found, however, to act unequally on the 

 cloth, the texture being injured in one 

 part, while in another it was imperfectly 

 xrhitened. The solution of it therefore 

 in water was substituted, and even this 

 requires to be considerably diluted. The 

 bleaching liquor, according to the direc- 

 tions given by Berthollefc, is prepared by 

 putting six parts of black oxide of man- 

 ganese, and sixteen of muriate of soda, 

 into a glass or earthen retort, or a leaden 

 bottle, and pouring upon them twelve 

 parts of sulphuric acid, diluted with nine 

 f water. The retort, or bottle, is con- 

 nected by a tube with a receiver, designed 

 to retain any common muriatic acid that 

 may pass over : from this vessel another 

 tube issues, which is inserted in a large 

 wooden cask filled with water. The tube 

 descends nearly to the bottom of the cask, 

 so that the gas has to rise through the 

 whole body of the water, at. the same time 

 the absorption of it is promoted by the mo- 

 tion of a circular frame placed in the mid- 

 dle of the cask, and which can be turned 

 round at the top. The oxygenated acid 

 is thus easily condensed. After the first 



disengagement of the gas has ceased, 

 heat is applied to the retort, by placing it 

 in a sand bath, or, if a leaden bottle be 

 used, by placing it in a vessel of boiling- 

 water. So much water is used, that the 

 oxygenated acid is very weak ; it requires 

 to be stronger for coarse than fine cloth, 

 and for linen than for cotton ; the ave- 

 rage quantity stated by Berthollet is 100 

 quarts for every pound of muriate of so- 

 da that has been used. The cloth to be 

 bleached is prepared by macerating it in 

 warm water for some hours, to take up 

 what part of the colouring- matter may be 

 soluble. It is then boiled in an alkaline 

 ley, prepared from 20 quarts of water and 

 one part of the potash of commerce, ren- 

 dered more active by having been mixed 

 with one-third of lime. After sufficient 

 boiling, it is washed with water, and put 

 into close wooden troughs, containing 

 the oxygenated acid, in which it is allow- 

 ed to macerate for three or four hours, 

 pressing the cloth frequently, and expos- 

 ing its surfaces to the action of the liquor. 

 It is thus alternately exposed to the ac- 

 tion of the alkaline ley and the oxygenated 

 acid, till its colouring matter is complete- 

 ly extracted, or it is sufficiently bleached., 

 which requires in general from four to 

 eight immersions, according to the nature 

 and coarseness of the cloth, cotton re- 

 quiring fewer immersions in the bleaching 

 liquor than linen. The subsequent steps 

 of the process are, to rub the cloth strong- 

 ly with soft soap in warm water. This 

 renders the surface more smooth and 

 uniform, and takes away the smell of the 

 oxygenated acid, which otherwise re- 

 mains a considerable time. The cloth is 

 again washed, and is lastly immersed for 

 a short time in water, in which, from one- 

 sixtieth to a hundredth part of sulphuric 

 acid has been dissolved. The cloth thus 

 acquires a much finer whiteness from the 

 sulphuric acid dissolving the remaining 

 colouring matter, which has resisted the 

 action of the alkali and oxygenated acid, 

 as well as a small quantity of iron and 

 calcareous earth contained in all vegeta- 

 ble matter, or even deposited in the cloth 

 by the alkaline leys. Lastly, the cloth is 

 generally exposed to the air for some 

 days, and watered, to carry off any re- 

 mains of either of the acids, and to re- 

 move completely the odour of the oxy- 

 genated acid. The theory of the action of 

 the oxygenated muriatic acid in bleaching 

 is very simple, as stated by Berthollet. 

 Its analogy to the common process by ex- 

 posure to the air and light, he observes, 

 is cqmplete. The end obtained by either 



