An Effay on Bleaching. 3 15 



When the old paper, foiled, has been expofed, in an appa- 

 ratus with frames, to the action of the fleam of boiling water 

 alone for twelve hours, it is fubje6fced to (light trituration 

 under a cylinder; it is then immerfed in a ftrong alkalino- 

 cauftic ley ; it is well pounded in the tub, that it may be 

 ftrongly impregnated ; and it is introduced a fecond time into 

 the apparatus, the boiler of which muft alfo be filled with 

 the ley. The pulp, after being expofed to a vapour bath for 

 ten or twelve hours, is taken out and prefled, that the alka- 

 line liquor which runs off may not be loft : it muft then be 

 put into bags to be beaten, and rinfed in running water; after 

 which it is fubjected to trituration under the cylinder till it 

 has acquired the proper degree of whitenefs. If it be necef- 

 fary to give the utmoft brilliancy to the white, it will be fuf- 

 ficient to employ a fecond vapour bath, together with a flight 

 immerfion in the liquid oxygenated muriate of lime ; then to 

 rinfe it, and to make it pafs through acidulous water. In 

 this operation it is to be wifhed that mallets and {tampers 

 were employed rather than cylinders, which are liable to be 

 attacked by the alkaline liquor. I do not here fpeak of 

 writing paper, becaufe it is fully proved that this procefs is 

 $00 tedious and expeniivc. 



Ley of Acidulous Water. 



At all bleach-fields it is cuftomary to terminate the ope- 

 ration bv making the cloth or thread pafs through acidulous 

 water. In fome places four milk is employed; but almoft 

 every where at prefent, after the example of the Irifh bleach- 

 ers, nothing is ufed but dilute fulphuric acid. The propor- 

 tion, in general, is one part in a hundred of acid diluted in 

 water. In Ireland the bleachers fomctimes judge of the pro- 

 portion by the tafte ; but this practice is liable to much error. 

 The tub in which the articles are made to pafs through aci- 

 dulous water is in general conftru&ed of wood ; but the ope- 

 ration being much accelerated when performed warm, I 

 would propofe that the heat, which is generally loft, mould 

 be turned to advantage. By making the heat to circulate in 

 a flue below the leaden veflcl, (already mentioned in fpeaking 

 of the apparatus of Bawens,) a temperature fufheient to heat 

 it mav be obtained. Hofiery and thread ought to be im- 

 merfeu and worked in handfuls for twelve hours : they are' 

 then to be rinfed in a large quantity of water, and made to 

 pafs a fecond time through the acid : feveral immerfion 3 

 brighten the whitenefs, and I would recommend them in 

 preference to the bad practice of leaving the matters im- 

 merfed for feveral days, Stuffs muft be wound up. This is 



in 



