BLEACHING 367 



if allowed to act on it with free access of air, it destroys it in a few hours. Neither 

 can cloth stand the action of alkalis of any kind very long : if very strong, they 

 rapidly destroy it. The same thing may, in a still stronger sense, be said of acids ; 

 and chloride of lime or bleaching-powder acts in the same direction. Linen, although 

 mechanically much stronger than cotton, has not an equal chemical resistance to de- 

 composition. It has not, therefore, been possible to use chloride of lime so as entirely 

 to complete the process of bleaching linen, but only to hasten it, the completion being 

 still nearly in all cases made by crofting. The bleacher has found out these things by 

 expensive experience, and every day shows the importance of guarding against the 

 excessive action of any one of the bleaching agents. Goods are continually suffering 

 from the desire of speed on the part of the trade, and especially of the buyer ; nor is 

 it easy to find them absolutely uninjured by the process of bleaching, although it 

 seems possible to conduct the process so that no weakening will ensue. The pre- 

 cautions taken are such as cause the processes to appear very long and tedious. The 

 boiling with lime is continued as long as it is safe ; the cloth is then at once washed 

 and scoured, so as to remove all the caustic earth from the fibre. The acid is not al- 

 lowed to remain long, but is, within from two to four hours, washed out by machines 

 which cause the cloth to be frequently and rapidly saturated with water ; and when 

 one of these processes is not enough, it is found better to return to it again than com- 

 pletely to finish it at once, to the danger of the fibre ; in the same way as workmen, 

 if they find it needful to put their hands into hot water, do it rapidly and for a short 

 time, but bring them out to cool before they return to the charge. To dry the goods 

 with even a very small amount of acid would infallibly render them rotten. When 

 the chlorine has oxidised or otherwise acted on the colouring-matter, so as to render 

 it soluble, it is washed out with alkalis, but the whole may not be acted on by the 

 first process, and a second may be needful. Again, as to crofting : one exposure may not 

 be found enough ; another washing and another crofting are then needed, and a third, 

 and so on, according to the method employed and the nature of the material xised. 



The souring by vegetable substances or by fermentation may also injure the cloth, 

 not by the amount of acid existing in the solution, but the decomposition which be- 

 comes communicated from the vegetable matter to the cloth, and so renders it weak 

 and rotten. The same is peculiarly the case when putrefactive action is allowed to 

 commence. This was often the case when the gluten of the paste was removed by 

 fermentation. It has been said that the action of carbonic and acetic acid on the fats 

 is a great objection to the fermentation process, as they are thought to render the fat 

 insoluble, and produce an indelible mark. 



Experiments undertaken for the purpose have shown that the strength of the fibre 

 is not impaired by being boiled in milk of lime for two hours, at the ordinary pressure, 

 provided it is not exposed at the same time to air ; but bleachers consider that, prac- 

 tically, the goods are not injured by boiling with lime for sixteen hours at the strength 

 of 40 Ibs. to 100 gallons. It has also been proved that caustic soda of the specific 

 gravity of 1030 1 does not hurt them, even boiled under the pressure of 140 Ibs. to the 

 square inch, or immersion for eight hours in chloride of lime solution containing 

 3 Ibs. to 100 gallons, and afterwards in sulphuric acid of the specific gravity of 1067', 

 or eighteen hours at the specific gravity of 1035'. 



j. The carbon left by the singeing is entirely removed, but it is not clear what be- 

 comes of it. It disappears in the alkaline solution, as no traces seem to exist after 

 this action. Probably the blackness or darkness is not caused by any pure carbon, 

 but by compounds soluble in alkalis. If any elementary carbon exist, it is carried 

 away almost entirely, no doubt, by mechanical means. 



k. The same method gets rid of the particles of pod which remain in the cotton, 

 and after the first washing they seem to stand out very prominently, swelling up into 

 large dark spots. The alkali probably renders them soft, and allows them to mix 

 readily with liquids, if not altogether actually dissolved. 



General Process of Bleaching. The process of bleaching, from what we have seen, 

 resolves itself into treatment with alkalis, and the action of chlorine or of light. In 

 describing the operations they seem to be very numerous ; but, as explained, some 

 require to be repeated gently, instead of being finished by one decisive operation, so 

 as not to injure the fibre ; and some are intermediate operations, such as the fre- 

 quent washings needed in passing from one process to the other. The alkaline solu- 

 tion in which the goods are boiled does not contain above 250 Ibs. of carbonate of soda 

 to 600 gallons, but nearly always less. Lime is, however, used much more frequently 

 than soda, which it will be seen is only employed in the second process, and the third 

 if there be one. It is less hurtful to the cloth, and is much cheaper than the alkalis. 



The chloride of lime is used at i Twaddle, or 1002-5. It is not considered so im- 

 portant now as formerly, and where 300 Ibs. were formerly employed, 30 to 40 are now 

 used. The goods are made nearly white by the alkalis. The chlorine gives only 



