An Ejfiiy on Bleaching, 109 



object of this eflfay. The price of rags is already high enough, 

 befides their fcarcity ; and Belgium, the ci-devant Bi itanny, 

 Auvergne, Alface, &c. are every year covered with lit ips of 

 this fubftance, which the paper-makers might procurt at a 

 very low price, and which would afford a rich mine ta w>c 

 worked by the induftrious art i ft. 



Hempen and linen cloth, when they come from the hands 

 of the weaver, arc charged with flour pafte called cfoeflingy 

 employed by the manufacturers to aid the tcnfion of the 

 threads during; the weaving;: fome manufacturers immerfe 

 their cloth in tubs, or expoie them in running water, or boil 

 them, to free them from this fubftance. Thefe are bad me- 

 thods, which betray ab folate ignorance of the proper princi- 

 ples. The beft is to immerfe the cloth from forty-eight to 

 fifty hours in a tub filled with' foft water, at the temperature 

 of from 6o° to 75 : the kind of fermentation which enfues is 

 fufneient to decompofe the pafte, arid is never ftrong enough 

 to attack the filaments of the thread : the cloth is then to be 

 rinfed in running water, by the help of a fluted cylinder, 

 which entirely frees it from that amylaceous fubftance. 



This operation gives to cloth a firft degree of bleaching, 

 which anfes merely from the destruction of a part of the 

 colouring matter during the fermentation, which opens the 

 threads of the cloth, fiackens and foftens their tiu'ue, and 

 (wells their fibres : ii may be feen that it has reached its 

 proper term by obferving all tlicfe phenomena, and when 

 the colour of the cloth is uniform throughout. 



After the cloth has been completely rinfed in running water 

 with the cylinder, it remains of a grayiih white colour : the 

 tint which oppofes its perfect whitenefs arifes from extracto- 

 rctinous matter Which remains combined with the filaments, 

 and from which they inuft be freed. This is the operation 

 properly called bleaching, whatever may be the operation 

 employed for accompliftnng it. Thefe different proceffes will 

 be defcribed in the courfe of this work. 



Of the colouring Mailer of Hemp and Flax. 



Before we proceed to a defcription of the different proceffes 

 for bleaching, it is of importance that we thould fay a few- 

 words reflecting the colouring matter of flax. This fubject 

 has been fully treated of by the celebrated Kirvvan, from 

 whofe experiments it is abundantly proved thai the colouring 

 matter extracted by the action of alkalies is a peculiar refin, 

 which differs from pure refin by being infolubk* in cffential 

 oils, and in having (bme refemblance to lacks. Having 

 procured fome of this fubftance, by feparating it frestfi what 



the 



