BLEACHING. 



589 



> the action of steam in a close vessel, (see Plate LVI. 

 Fig. 3. 



A is the receive , made of fir-deal boards firmly 

 hooped, into which the cloth is laid loosely on the 

 iron grating C. BB are iron hesps fixed to the side 

 of the receiver, into which another hesp of iron, con- 

 taining a screw D, is placed. This is moveable, and 

 folds over by a joint, to make fast the cast-iron cover 

 on the mouth of the tub or receiver : the joining of the 

 lid is closely luted by plated rope being nailed to the 

 mouth of the tub. The iron cover is put on its 

 place, or removed at pleasure, by the hook of a 

 crane being put into the ring E fixed in the-centre 

 f the lid. A hole is pierced through the cover, in- 

 to which a wooden pin F is thrust, the use of 

 which is to know when the steam is of sufficient 

 strength. 



The cotton or linen goods having been previously 

 cleaned by steeping and washing, are, after being 

 well drained, steeped in a solution of caustic alkali 

 of the specific gravity of 1020. After the super- 

 fluous alkaline ley has been drained from them, they 

 are arranged on the grating C in the receiver. The 

 cover is then placed on the vessel, and firmly screw- 

 ed down ; and the steam is admitted by turning the 

 stopcock H, of the pipe G, which communicates 

 with a steam boiler of the common construction. 



When the steam is admitted, the action of the al- 

 kali is increased by the heat, so as completely to dis- 

 solve the colouring matter of the cloth. The steam- 

 ing is continued for some hours, after which the 

 cloth is removed to the wash stocks, or dash wheel, 

 in order to be cleansed : they are again immersed in 

 the solution of alkali, and steamed in the receiver 

 until they are sufficiently white ; after which they 

 are soured and washed as in common bleaching. 

 This process of whitening cotton or linen cloth, may 

 also be forwarded by the assistance of the oxymuria- 

 tic acid, at proper intervals. 



By this method of bleaching, a considerable saving 

 of alkali is gained, as the whole is completely satu- 

 rated with the colouring matter of the cloth. Nine, 

 r at most ten steeps in the alkali, with alternate expo- 

 sure to the action of the steam bath, being sufficient 

 to bleach linen cloth effectually : Five steeps, with 

 exposure to the steam, is sufficient for cotton cloth. 



Having thus given a succinct account of the 

 various operations of bleaching, we shall close this 

 article, by making such observations as seem natu- 

 rally to arise from the subject. 

 't i The first inquiry which presents itself is, What 



the colour- are tne substances with which linen and cotton cloth 

 onin t a ." er is coloured ? Th > 3 shown by Mr Kirwan in his 

 excellent memoir on this subject, contained in the 

 Irish Transactions for 1789. 



He precipitated, by means of muriatic acid, the 

 colouring matter from an alkaline ley, saturated with 

 the extract from linen yarn, and found it to possess 

 the following properties. When allowed to dry on 

 a filter, it assumed a dark green colour, and felt 

 clammy like moist clay. 



" I took," says he, " a small portion of it, and 

 added to it 60 times its weight of boiling water ; but 

 not a particle of it was dissolved. The remainder I 

 ' 2 



dried on a sand heat ; it then assumed a shining Bleaching, 

 black colour ; became more brittle ; but internally 

 remained of a greenish yellow, and weighed an ounce 

 and a half. 



By treating eight quarts more of the saturated 

 ley in the same manner, I obtained a further quan- 

 tity of the greenish deposit, on which I made the 

 following experiments. 



1 . Having digested a portion of it in rectified spi- 

 rits of wine, it communicated to it a reddish hue, 

 and was in a great measure dissolved ; but, by the 

 addition of distilled water, the solution became 

 milky, and a white deposit was gradually formed : 

 the black matter dissolved in the same manner. 



2. Neither the green nor the black matter was so- 

 luble in spirit of turpentine or linseed oil, by a con- 

 tinued long digestion. 



3. The black matter being placed on a red-hot 

 iron, burned with a yellow flame and black smoke, 

 leaving a coaly residuum. 



4. The green matter being put into the vitriolic, 

 muriatic, and nitrous acids, communicated a brown- 

 ish tinge to the two former, and a greenish to the 

 latter ; but did not seem at all diminished. 



Hence it appears, that the matter extracted from 

 linen yarn by alkalies, is a peculiar sort of resin, 

 different from pure resins only by its insolubility in 

 essential oils, and in this respect resembling lacs. I 

 now proceeded to examine the powers of the differ- 

 ent alkalies on this substance. Eight grains of it 

 being digested in a solution of crystallized mineral 

 alkali, saturated in the temperature of 62, instantly 

 communicated to the solution a dark brown colour ; 

 two measures (each of which would contain 11 pen- 

 nyweights of water) did not entirely dissolve this 

 substance. Two measures of the mild vegetable al- 

 kali dissolved the whole. 



One measure of caustic mineral alkali, whose spe- 

 cific gravity was 1.053, dissolved nearly the whole, 

 leaving only a white residuum. 



One measure of caustic vegetable alkali, whose 

 specific gravity was 1.039, dissolved the whole. 



One measure of liver of sulphur, whose specific 

 gravity was 1.170, dissolved the whole. 



One measure of caustic volatile alkali dissolved also 

 a portion of this matter." 



From the foregoing observations of Mr Kirwan, 

 it is evident, that the lac or resinous matter which is 

 extracted by the alkalies from linen yarn, is in pro- 

 portion to their capacity for acting upon this colour- 

 ing matter ; and that the vegetable alkali, whether 

 in its nild or the caustic state, is the best solvent of 

 this matter. 



We here take the opportunity of remarking, that 

 at most bleachfields, they are extremely defective in 

 rendering the alkaline leys properly caustic by 

 quicklime. Into a solution of about four hundred 

 weight of potashes, dissolved in about 300 gallons of 

 water, we have frequently seen only 40 or 50 pounds 

 of quicklime used ; and so imperfectly was it ap- 

 plied, as only to be agitated by a rake for five or 

 ten minutes in the cold solution. Quicklime having 

 the power of precipitating the uncombined charcoal 

 and other impurities, the operator was satisfied, that 

 he had given to the alkaline ley its full powers; but 



