BLEACHING. 



by lime ; it is suspended loosely, and, 

 with an extensive surface, in a close boil- 

 er, a quantity of the same solution being 

 in the bottom, and heat is applied, the 

 boiler being closed, with a safety valve in 

 the cover, so that the vapour under pres- 

 sure may receive a high temperature. 

 It is kept in this situation for a number 

 of hours. The thread or cloth when cold 

 is washed, and either exposed on the 

 field, or subjected to the action of the 

 oxymuriatic acid in some of the forms 

 under which it has been used. It is thus 

 at once rendered perfectly white. The 

 superiority of this method probably arises 

 from the high temperature, and the 

 solvent power of the watery vapour, fa- 

 vouring the action of the alkali on the 

 colouring matter, while this vapour pene- 

 trates the fibres of the cloth so effectual- 

 ly, that the matter is in a great measure 

 dissolved and removed. 



The animal fibres that are subjected to 

 the bleaching process,, are wool and silk. 

 These cannot be treated in the same 

 manner as vegetable substances : a strong 

 alkaline ley will dissolve them, and oxy- 

 muriatic acid will both weaken them and 

 turn them yellow. The colour of manu- 

 factured wool resides partly in its own 

 oil, and partly in the greasy and mucila- 

 ginous applications which it receives in 

 being prepared for the loom. Both the 

 one and the other are easily got rid of, 

 by the action of fuller's earth and soap in 

 the process of fulling. Fuller's earth 

 is a very fine-grained absorbent earth, 

 which by itself is capable of mixing 

 rather than combining with vegetable or 

 animal oils, and rendering them raiscible 

 with water: its action is found, however, 

 to be increased by the addition of soap ; 

 and woollen cloth being beat in a fulling- 

 mill with hot water, and a proper mix- 

 ture of earth and soap, or of soap alone, 

 and afterwards well washed and dried in 

 the air, receives all the bleaching which 

 it .requires, or is indeed capable of. It is 

 then of a white colour, somewhat verg- 

 ing towards yellow : this last tinge may 

 be made to disappear, by the addition of a 

 very small quantity of stone blue in the 

 water in which the cloth is last washed, 

 or by exposing it to the fumes of burning 

 sulphur. By this latter method, how- 

 ever, it acquires a certain harshness of 

 feel, and is apt to turn very yellow when 

 washed with soap. Both the colour and 

 harsh ness of raw silk depend entirely on 

 a yellow varnish with which it is naturally 

 covered. This varnish may be in part 

 removed by long boiling in simple water. 

 U is considerably more soluble in alco- 



hol; but the most effectual and expedi- 

 tious way of clearing is by putting it in a 

 linen bag, and boiling it for some hours 

 in a solution of white soap and water, then 

 rincing it in clean water, and repeating 

 the process till it is quite white, and ex- 

 hibits the peculiar lustre of this beautiful 

 substance. Some of the French chemists 

 have endeavoured to lessen the con- 

 sumption of soap, by proposing various 

 substitutes; but nothing is so effectual 

 and expeditious as the purest white soap, 

 and the article itself is so valuable, as 

 amply to repay this expense. 



The oxymip-iatic acid has also been 

 used from its bleaching power in the ma- 

 nufacture of paper ; either the linen rags 

 from which the paper is to be made be- 

 ing blanched by it, or, what has been re- 

 garded as preferable, the pulp into which 

 they are reduced being submitted to its 

 action. This method, though once ex- 

 tensively practised in this country, has 

 been relinquished by many of our paper- 

 manufacturers, as it has been found, that 

 in paper prepared with it, in the course 

 of a few years, the ink is altered, and its 

 blackness even so much impaired, as to 

 afford some reason for the suspicion that 

 in time it will altogether fade ; nor is 

 this confined to writing ink, but has been 

 observed even in printing ink. The ef- 

 fect is no doubt to be ascribed to a slight 

 impregnation of the oxy muriatic acid, 

 and this indeed can often be rendered 

 perceptible by its odour, by breathing 

 on paper which has been bleached in this 

 manner. It might no doubt be removed 

 by very careful washing of the pulp ; but 

 we have been informed by some intelli- 

 gent paper manufacturers, that the addi- 

 tional labour which would be requisite 

 for this would, upon the whole, render 

 the method more expensive than the old 

 one. 



The process of bleaching by steam with 

 an alkali at a high temperature might 

 probably be advantageously employed. 

 A branch of the manufacture, however, 

 in which the acid necessarily must be 

 used, is that of discharging the colours 

 from coloured rags, or to remove the ink 

 from waste written paper. Even printed 

 paper has been whitened by its agency, 

 combined with that of an alkali, to re- 

 move the oily matter, and made to afford 

 at least a coarser kind of paper. Chaptal 

 applied it to the purpose of restoring the 

 colour of old books or prints, the paper 

 being whitened by a very dilute acid, 

 which did not act sensibly on the print- 

 ing ink. 



Wax, reduced to thin plates, has been 



