588 



BLEACHING. 



Bleaching 



printed 



goods. 



Plate 

 LV1. Fig. 

 4. 



B'.eaching. Of all the earths which are partially soluble in wa- 

 ter, magnesia possesses the property of changing co- 

 lours least ; the alteration made by it on paper stain- 

 ed with litmus being scarcely perceptible. It is, 

 therefore, peculiarly fitted, when united with oxygen, 

 for the purpose of clearing the stain from the white 

 of printed goods. 



In making this preparation, the magnesian earth 

 must be previously broken in water, as fine as possible, 

 in the manner of starch. It is then introduced into 

 the receiver K of the apparatus for making the 

 oxymuriatic acid. (See Plate LVI., fig. 4.) Into 

 the retort A one part of good manganese is intro- 

 duced, on which is poured two parts of muriatic acid, 

 of the specific gravity of 1200, diluted with its bulk 

 of water ; the distillation instantly commences, and 

 the magnesia is dissolved by the oxymuriatic acid. In 

 order to keep the magnesia in suspension, it is neces- 

 sary to agitate the liquor in the receiver occasionally 

 by a staff similar to a churn staff, which is placed in 

 the receiver, the handle coming up through the cen- 

 tre of the cover. 



When the magnesia is dissolved, and the impurities 

 which it may contain have subsided, it is drawn off 

 for use. For this purpose, a clean copper is filled 

 with pure water, and the heat is raised to about 160 

 or 170 degr-ees of Fahrenheit. So much of the oxy- 

 muriate of magnesia is then added as will give to the 

 water in the copper a sensible taste of the salt. As 

 soon as it is introduced, the whole must be quickly 

 mixed together by a clean broom. The printed 

 goods, having been previously slightly braned, are 

 then quickly run over the wince into the copper ; 

 continuing to run them over the wince until the white 

 is sufficiently clear. This operation takes only a few 

 aiinutes. The goods are then carried to be stream- 

 ed in pure water, to prevent the further action of the 

 oxygen on the colours. By the addition of a little 

 more of the oxymuriate X>f magnesia, fresh parcels 

 of goods may be entered into the copper for clear- 

 ing, and the process may be thereby continued for 

 a whole day ; after which the contej^g are run off 

 from the boiler. 



CHAP. V. 



On Bleaching Muslin. 



Bleaching 

 muslin. 



In the bleaching of the coarser kinds of muslin, 

 such as the fabric of goods called Jaconet, after 

 they have been steeped and washed, they are first 

 boiled in a weak solution of pot and pearl ashes ; af- 

 ter being again washed, they are twice boiled in soap 

 alone, and then soured in very dilute sulphuric acid. 

 Being washed from the sour, they are again boiled in 

 soap, washed, and then immersed in the oxymuriate 

 of potash. The boiling in soap, and steeping in the 

 oxymuriate, is now repeated, until the muslin is a pure 



white. They are then soured and washed in pure Bleaching, 

 spring water. ' v-"- ' 



In bleaching the finer fabrics of muslin, such as 

 those kinds called Mull Mull and Book, nearly the 

 same process is followed as the above for bleaching of 

 Jaconet ; only that, on account of the fineness of 

 the fabric, no pearl ashes are used in boiling, but 

 soap alone. Otherwise, they are treated in the same 

 manner, in being alternately washed, boiled, and 

 steeped in the oxymuriate of potash ; and when full; 

 white, they are soured in dilute sulphuric acid. 



In the bleaching of cotton cloth, where fixed co- Bleachiug 

 lours * are previously dyed in the yarn before it is coloured 

 wove into cloth, great care is necessary. Before cottons - 

 it was customary to introduce caustic alkali into the 

 receiver of the apparatus for making the oxymuriate 

 of potash, the most complete uncertainty occurred 

 with the bleacher in his attempts to bleach cotton 

 goods wherein the most fixed colours were wove. 

 Sometimes the colours were in tolerable preservation 

 when the oxymuriatic acid was used in moderation ; 

 at other times, the colours were almost entirely ex- 

 tracted from this acid being used too strong. At last 

 it was discovered, that when a considerable quantity 

 of the alkali was introduced into the receiver, for the 

 neutralizing of the oxymuriatic acid, that the fixed 

 or permanent colours, which were immersed into it, 

 were by no means injured. On this principle, cotton 

 goods of the kind called Pulicates, into which fixed 

 colours are wove, and which have thoroughly to un- 

 dergo the whole process of bleaching, the colours 

 are more brilliant than in those goods, of the same 

 kind, which are wove along wiih yarns that have 

 been previously bleached. 



The common process of bleaching pulicates, in- 

 to which permanent colours are wove, is, to wash 

 the dressing or starch well out in cold water. To 

 boil, ihem gently in soap, and, after again washing, 

 to immerse them in a moderately strong solution of 

 the oxymuriate of potash ; and this process is fol- 

 lowed until the white is good : they are then soured 

 in dilute sulphuric acid. If the goods are attend- 

 ed to in a proper manner, the colours, in place of 

 being impaired, will be found greatly improved, and 

 to have acquired a delicacy of tint which no other 

 process can impart to them. 



Pulicates, or ginghams, which have been wove 

 along with yatn which has been previously bleached, 

 are first freed by washing from the starch or dn 

 sing : they are then washed, or slightly boiled with 

 soap. After which, they are completely rinsed in 

 pure spring water, and then soured. 



Besides these common processes for bleaching, an- 

 other has been lately introduced with great success, 

 by Mr John Turnbull of Bonhill-place, in Dunbar- 

 tonshire, for which a patent was granted him. 



This method of bleaching consists of immersing 

 the cotton or linen goods in a pretty strong solution 

 of caustic alkali, and afterwards exposing them to 



By Fixed Colours are here meant, those which resist the action of the alkalis in an eminent degree, with proper trea>- 

 ment. The colours usually denominated fixed, on cotton, are the Turkey or Adrianople red, and its compounds of lilac o> 

 purple, by the addition of 'iron bases; various shades of blue from indigo, togetner with buff and gold colour, tinged with 

 the oxides oi iron. 



