BLEACHING. 



is the combination of oxygen with the co- 

 louring matter of the vegetable. By this 

 combination the colour is nearly destroy- 

 ed, and the matter on which it depends 

 is at the same time rendered soluble in 

 the alkaline solution. Hence the neces- 

 sity of the alternate application of these 

 two chemical agents ; the one removing 

 from the cloth what the other has render- 

 ed soluble, and which, although whitened, 

 would regain part at least of its colour in 

 time. Hence it is found, that, the oxygen- 

 ated muriatic acid is, in this operation 

 converted into common muriatic acid, and 

 the alkaline solution is yl lo-gih so leaded 

 with colouring matter, th.n it becomes 

 unfit to be used. The onl> difference be- 

 tween the two methods is, that in the one 

 the oxygen is presented in a much more 

 concentrated state than in the other, which 

 facilitates the process, or renders it more 

 rapid without injuring the strength of the 

 fibre. At least, the only injury of this 

 kind that can happen must arise from im- 

 proper management; having used too 

 strong an acid, or the not washing the 

 cloth sufficiently after the process istimsh- 

 ed. The greatest difficulty attending the 

 ust of oxymuriatic acid arose from its 

 suffocating odour, which rendered it al- 

 most impossible to work with it in an 

 open vessel, and any apparatus contrived 

 to turn the cloth and expose fresh surfaces 

 of it to the action of the liquid in close 

 vessels, has been found imperfect. The 

 addition of an alkali to the liquid removes 

 in a great measure the odour of the acid, 

 or at least prevents its unpleasant effects; 

 and although it at the same time dimi- 

 nishes to a certain extent its bleaching 

 power, this is more than compensated for 

 by the advantage. The quantity of alkali 

 added amounts to about \lb. of the pot- 

 ash or pearl-ash of commerce to the quan- 

 tity of acid prepared from 4lbs. of muriate 

 of soda. And to avoid the effervescence 

 which would arise from the disengage- 

 ment of the carbonic acid during the 

 combination of the oxymuriatic acid, the 

 potash is deprived of it by the previous 

 addition of lime, the alkaline solution af- 

 ter its operation being poured off clear. 



Independently of the weakening of the 

 power of the acid by this addition, a con- 

 siderable expense was introduced by the 

 use of the alkali; and it became an ob- 

 ject of importance to the manufacturers 

 of this country to substitute a cheaper 

 substance, which should have the same 

 effect. Lime was tried at first in an im- 

 perfect manner, but at length with such 

 improvements, that it is now always used. 



VOL. II. 



The difference of using it arose from the 

 insolubility of the lime in water, the quan- 

 tity taken up being so inconsiderable, that 

 the solution could have little effect in cor- 

 recting the odour of the acid. A very 

 important improvement, therefore, was 

 that of using lime suspended in water, 

 and kept in suspension by an agitation in 

 a close vessel, into which the gas was 

 transmitted. Its condensation was thus 

 facilitated, and the compound which is 

 formed with the lime being soluble in 

 water, the undissolved or unsuturated 

 lime was allowed to subside, and the 

 clear liquor was fit for the purpose of 

 bleaching. 



An improvement, however, of still 

 more importance, has been made by Mr. 

 Tennant of Glasgow, and a patent obtain- 

 ed for it ; viz. that of combining the oxy- 

 muriatic acid with dry lime, and dissolv- 

 ing a certain proportion of this compound 

 in water, to form a bleaching liquor. It 

 perhaps could scarcely have been sup- 

 posed that such a combination could have 

 been formed, so as to retain the powers 

 of the acid. But the trial has fully suc- 

 ceeded, and the advantages derived from 

 it are important ; the compound can be 

 carried easily to a distance, and the ma- 

 nufacturer need not prepare it himself, 

 which is always an advantage, especially 

 where he does not work on a large scale. 

 The combination is formed by introducing 

 the oxymuriatic acid gas through leaden 

 tubes into slacked lime, prepared from 

 chalk, by which it is absorbed Solutions 

 of this are prepared of different strengths, 

 according to the purposes to which they 

 are to be applied, the strength being 

 judged of by the hydrometer, and by the 

 quantity requisite 'to destroy the colour 

 of a diluted solution of indigo in sulphu- 

 ric acid. The process of bleaching, as 

 now performed by these liquors, differs 

 little from that which has been already 

 described as executed by the solution of 

 the oxymuriatic acid alone in water. To 

 these methods, however, is to be ad'ted 

 the more recent discovery of bleaching by 

 an alkali, assisted by a watery vapour and 

 a high temperature, and which, eiiiier 

 alone, or combined to a certain extent 

 with the method by the oxymuriated scid, 

 is now practised with so much advantage. 

 In this method, which has been long in 

 use in some of the eastern countries, and 

 of which notice was first given by Chap- 

 tal, the cloth or thread is impregnated 

 with a solution of potash or soda, render- 

 ed active by the carbonic acid having 

 been entirely abstracted from the alkali 



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