CALICO-PRINTING 625 



or cotton fibre in decomposing acetates of iron and alumina, has been denied by some 

 chemists, especially by the late Mr. Walter Crum, the eminent printer of Thornliebank, 

 who, in a very interesting paper printed in the Journal of the Chemical Society 

 for 1863, propounded the theory, that capillary action of the fibre separates tha 

 mordant from the thickening substance, which is left at the outside of the fibre, that 

 by desiccation the acetates are decomposed, and the bases left in the interior cavities. 

 He also attributes to the cloth an attraction of surface, whereby bases are separated 

 from their solvents, in the same manner as that in which charcoal decomposes certain 

 salts. He points out also, that the fibre may act as a dialyser to retain within its 

 pores, or in the interior cavity of the cotton fibre tube, a colloid solution of alumina 

 or iron ; the crystalline portion of the mordant having passed through when the 

 printed cloth is immersed in water (dunging operation). Mr. Crum gives some 

 beautiful drawings of the appearance of dyed cotton fibres under the microscope, 

 showing in many cases that a clot of mordant base has been formed in the interior 

 cavity of cotton fibre and been subsequently dyed there. His drawings, however, for 

 the most part show that the walls of the tubes are dyed throughout their substance ; 

 a fact not, as we think, sufficiently explained by his theory. Other microscopists who 

 have examined dyed cotton fibre, have failed to detect imprisoned particles of colour 

 inside the tube, but have noticed that the wall of the tube throughout its substance is 

 dyed; which, if correct, certainly points to a chemical action of the cell wall. That 

 cotton fibre has a separating power, even when immersed in water, may be shown by 

 putting bleached cotton cloth overhead in a solution of oxide of lead in lime (plum- 

 bite of calcium) for half an hour or so, removing, rinsing very well in water, and passing 

 through a solution of bichromate of potash, whence the cloth will emerge dyed a 

 bright yellow. This reaction is noticed by Mr. Crum as an illustration of the surface 

 attraction exercised by cotton fibre ; the withdrawal of indigotine, or white indigo, 

 from a solution of it, by cotton cloth immersed therein, being also given by Crum as 

 an illustration of the same force ; but the former, at all events, may equally serve as 

 an illustration of the chemical power of cotton fibre to sieze and combine with bases, 

 and this power is, we think, further illustrated by the rapidity with which acetates 

 are decomposed under the influence of the ageing machine and torrents of acetic acid 

 given off. There is room, apparently, for further investigation of this obscure point. 

 That pigments such as prussian blue, chromate of lead, &c., can be precipitated and 

 imprisoned inside the cotton tubes, is not of course, denied ; but the action here seems 

 quite different from that of ageing. Probably even in well -aged goods, a precipita- 

 tion of this latter sort takes place to some extent, when the arseniate phosphate or 

 silicate of soda of the dunging solution reacts upon mordant separated from its 

 thickening, and remaining inside the cotton tube. Thus, it is quite conceivable that 

 two separate actions have taken place in goods about to be dyed ; viz., a chemical 

 combination of the tube wall with the base of the mordant, and an imprisonment of 

 an insoluble salt inside the tube, by double decomposition. 



The next operation is that termed dunging, which is the same in principle for 

 all varieties of madder or garancin goods : and as it is an operation the careful 

 performance of which is of vital importance to the success of the subsequent operations, 

 a somewhat detailed description of it will not be out of place. The process of dunging 

 has for its object 



1. Precipitating on the fibre, by double decomposition, that portion of the mordant 

 which has escaped decomposition in the ageing room. 



2. Rendering insoluble and inert those portions of the mordant which are not In 

 direct contact with the fibre, and which, if allowed to diffuse in water only, would 

 fix on and stain the white or unprinted parts of the cloth. 



3. Softening and removal of the thickening substances. 



4. Neutralising the acids which may have been added to the mordants, or used as 

 resists or discharges, and which otherwise would dissolve in the Water and weaken the 

 colours. 



5. The formation, in the case of iron mordants, of a compound of oxide of iron, and 

 certain organic or inorganic acids which will not become peroxidised beyond a 

 certain point. The use of cow-dung, derived from India, has been continued down 

 to the present time, though for several years printers have largely introduced various 

 substitutes. 



No very exact analysis has been made of cow-dung. Morin's is as follows : 



Water 70-00 



Vegetable fibre 24-08 



Green resin and fat acids 1'52 



Undecomposed biliary matter ..... 0'60- 

 Peculiar extractive matter (bubuline) .... 1'60 

 VOL. I. S S 



