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CHAPTER IV. an

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BLEACHING. ^

"D EFORE either spun cotton yarn or woven tissue are fit for dyeing or printing, S0they undergo a series of mechanical and chemical processes to free themfrom all adhering substances, such substances either naturally belonging to the ^

fibre or being purposely introduced during the operations of spinning and weaving,

Pure cotton is of a dirty yellow colour, which if not removed by bleaching ^

would materially affed and change the brighter shades of dyes imparted totissues ; moreover, the effedt of many beautiful printed patterns is due to thebrilliant white ground upon which they appear. Bleaching also removesfrom cotton all grease, which if allowed to remain would prove very injuriousboth in dyeing and printing, either preventing the fixation of colour, or elseadting as a mordant, especially after partial oxidisation by the air, and thus u

attradting the dye in an irregular manner.

Before bleaching, the cotton fabric is singed, in order to remove the nap andrender the surface perfedly smooth. This is done either by passing the fabric ^

through a gas flame or over a heated copper plate. In the latter case there j n

was formerly great waste of fuel in maintaining the heat of the plate owing to t

its free radiation into the atmosphere, but this has been remedied by an in-vention of Mr. Thom. This consists of enclosing the plate in a brick arch so uc

that no air can enter the chamber except that passing in with the stuff, andthe limited quantity thus admitted is conduded by flues into the furnace j t

which heats the plate. Messrs. Joshua Schofield and Sons have introduced a ^

new gas singeing machine, patented by Mr. James Cook. Instead of the c j

fabric being drawn through the flame as in the old method, the flame is made 0 f

to flow upon the surface of the fabric, the nap being thereby removed without ar

destroying the fibres. The flame employed in this method is a mixture of pj

coal-gas and oxygen, the heat of which is so great that the fabric can be passed A

over it with such rapidity as to remove the nap without injuring the fibre. ; r ,

The machine is both quick and economical, and like Mr. Thom’s, does notallow of the escape of any offensive odour during the operation. At the S j,

works of Messrs. Edmund Potter and Co. more than 4000 pieces of calico were w ;

singed in a day with a consumption of only 1000 cubic feet of gas per 1000 th

pieces. ce

The following substances adhere to and become mixed up with the cotton:" ce

1st, a brown-coloured incrustating substance insoluble in water and alkaline to

solutions, but capable of becoming soluble in water under the joint influence th

of air, damp, and sunlight, or by tfie adtion of chlorine and hypochlorous acid; m

2nd, according to M. Penot, a resinous substance soluble in alkaline lyes! di

but the quantity of both these substances found in cotton is small.