m 



BLEACHING. 



Manga 

 ncse. 



Bleaching, in water by agitation ; the insoluble matter contained 

 * - in the lime is allowed to subside until the liquor is 

 transparent. When drawn off for use, it is further di- 

 luted with water bef< re the goods are immersed in it, 

 in order to be whitened. 



V I. The oxide of manganese, when of a good qua- 

 lity, is of a black shining colour ; when combined with 

 oxygen at a maximum, it contains 44 parts of the 

 metal with (56 parts of oxygen ; but as taken from 

 the mines which contain it, it is never found so pure. 

 The principal defect of manganese arises from its be- 

 ing united with chalk, or ores of iron ; and when any 

 of these are mixed in quantity with it, its effect is 

 proportionally weakened in making bleaching liquor. 

 The presence of carbonate of lime may be discovered 

 in manganese, by pouring on a portion of this 

 stance nitric acid diluted with eight or ten parts of 

 water. If the manganese be good, no effervescence 

 will ensue, nor will the acid dissolve any thing ; but 

 if carbonate of lime be present, it will be taken up 

 by the acid. To the solution add a sufficient quan- 

 tity of carbonate of potash to precipitate the lime. 

 Its weight will show how much chalk the manganese 

 under examination contained. 



The adulteration of manganese when it is mixed 

 with the ores of iron is less easily discovered. But 

 if the iron be in such a state of oxidation as to be 

 soluble in muriatic acid, the following process may 

 discover it : Dissolve a portion of the manganese in 

 strong muriatic acid, with the assistance of heat ; di- 

 lute the solution largely with rain-water, and add a 

 solution of crystallized carbonate of potash. The 

 manganese will remain suspended by the excess of 

 carbonic acid, but the iron will be precipitated in 

 the state of a coloured oxide, on mixing the two so- 

 lutions. From an observation of Klaproth's, ( Es- 

 says, i. p. 572. ) it appears that oxides of iron are se- 

 parable by nitrous acid, with the addition of sugar, 

 which takes up the manganese only. 

 Sulphuric VII. Sulphuric acid, or oil of vitriol, as it is com- 



acid. monly called, when pure, is a transparent, colourless 



fluid, slightly viscid, and without smell. The speci- 

 fic gravity of the sulphuric acid of commerce is gene- 

 rally 1850, or almost twice the weight of distilled 

 water. The manufacture of it is now carried on to 

 such extent in Great Britain, that any further de- 

 scription of a substance so well known is unnecessa- 

 ry. The only substances with which it is ever adul- 

 terated are lead, and supersulphate of potash. A 

 small portion of lead is taken up during its formation, 

 in chambers of that metal, and its subsequent concen- 

 tration in boilers. On this account, a white precipi- 

 tate is often found in the bottom of the bottles con- 

 taining it, which is sulphate of lead. After the com- 

 bustion of the sulphur and nitre in the manufacture 

 of sulphuric acid, supersulphate of potash is left as a 

 residuum, by the affinity of the potash contained in 

 the nitre with the sulphuric acid. Some manufactu- 

 rers add a strong solution of this salt to the water 

 which is put into the lead chambers where the sul- 

 phuric acid is formed. Now, in proportion to the 

 quantity of potash contained in this solution, in so 

 far is the specific gravity increased, and, in cor. se- 

 quence, the sulphuric acid is rendered ineffectual tor 

 wiswering the purposes of bleaching. 



Muriatic 

 acid. 



This adultcratioq is carried so far as frequently to BK- 

 leave only four-fifths of pure acid. Hence it ou^ht * v ' 

 to be the bleacher's study to purchase what contain* 

 only pure sulphuric acid. 



VIII. The muriatic acid of commerce has gene- 

 rally a slightly yellowish tinge, which proceeds part- 

 ly from the impurities contained in the common salt 

 from which it is made, and partly from its being dis- 

 tilled in iron retorts. When distilled in glass vessels 

 from pure salt, the muriatic acid is perfectly colour- 

 less, and its specific gravity is about 1170. 



CHAP. III. 



An Account of the Marnier in which these Sub- 

 stances are applied. 



The common operations of bleaching consist of 



Steeping, 

 Bucking, 







Boih;i_ 



Inm.ersion in the oxymuriatic acid, 



Souring, washing, &c. 



Method of 

 applying 

 the deter- 

 gent sub- 



Sect. I. On Steeping. 



In the preparation of yarns for weaving, whether On steep- 

 composed of flax or cotton, it is necessary that the '"g- 

 weaver employ some gelatinous substance to give the 

 threads the requisite adhesion to stand the operation 

 of weaving. This substance is commonly made of 

 wheaten flour, boiled in water to the consistence of 

 pap, which is applied to the threads with a brush. 

 This is the principal extraneous matter upon the 

 goods, which it is the business of the bleacher to re- 

 move. To accomplish this, the linens, after being 

 properly assorted, are washed in the wash stocks 

 (Plate L,V. Fig. 6.) for some hours, in order to Plats 

 free them from loose stuff which may be attached to LV - 

 them. They are then put into a large circular vat, *'%' * 

 made of fir-deal boards, called technically a kieve, 

 into which they are laid regularly one above another, 

 without being too much compressed. After the 

 goods are disposed in the kieve, it is filled with alka- 

 line ley, at a blood-heat, which has been already used 

 in bucking or boiling former parcels. A piece of 

 wood, in the form of a cross, is then fixed above the 

 goods, in order to keep them below the liquid. 



In a few hours an intestine motion is observable, 

 and an increase of temperature takes place ; the li- 

 quid swells ; bubbles of air rise to the surface ; and a 

 thick scum is thrown up. This fermentation conti- 

 nues from twelve to eighteen hours, according to the 

 state of the weather. So soon as it is observed that 

 it has ceased, the goods must be instantly withdrawn 

 from the kieve, and again carried to the wash stocks, 

 or to the dash wheel, in order to be cleared from the 

 loosened tilth. Should the goods be left too long in 

 the steep, they are liable to considerable damage ; as, 

 after the acetous fermentation ceases, the putrid fer- 

 mentation begins, and the coloured matter, in place 

 of bl 'Ued from the goods, is fixed in them ; 



and, at the same time, the dissolution of the vegeta- 

 ble fibre of the cloth is begun, and were they to re- 



