318 DYEING A.ND CALICO PRINTING. 



every step of madder printing, still there is one process so pre-eminently 

 important in its practical results, and so interesting in a scientific point 

 of view, as to exact a more extended notice. 



The process of " ageing " in calico printing is that by which a mor- 

 dant, after being applied to a cotton fabric, is placed in circumstances 

 favourable to its being completely incorporated with and fixed in the 

 fibre. Thus it has generally been found necessary that calico printed 

 with a mordant should, before dyeing, be exposed in single folds to the 

 atmosphere for several days in the ageing room ; the object being to 

 liberate the acetic acid from the acetates of iron or sulpho-acetate of 

 alumina, and to oxidize the oxide of iron. It was for many years be- 

 lieved that oxygen was the only necessary agent, and though some 

 printers had observed that moisture facilitated the process, the fact was 

 not generally known until Mr. John Thom suggested the introduction of 

 moisture as an important agent in the phenomena of ageing. The first 

 printer, however, who, as far as I am aware, practically applied this dis- 

 covery was Mr. Walter Crum, F.R.S. ; and the great saving effected by 

 the judicious employment of steam in this process cannot be better 

 stated than by giving, in Mr. Cram's own words, the particulars of the 

 plan adopted at Thornliebank Print Works : — 



"A building is employed, forty-eight feet long inside, and forty feet 

 high, witli a mid wall from bottom to top running lengthwise, so as to 

 form two apartments, each eleven feet wide. 



" In one of these apartments the goods first receive the moisture they 

 require. Besides the ground floor, it has two open sparred floors twenty- 

 six feet apart, upon eaeh of which is fixed a row of tin rollers, all long 

 enough to contain two pieces of cloth at their breadth. The rollers 

 being threaded, are set in motion by a small steam engine, and the 

 goods to be aged, which are first placed in the ground floor, are drawn 

 into the chamber above, where they are made to pass over and under 

 each roller, issuing at last at the opposite end, where they are folded 

 into bundles on one (at a time) of the three stages that are placed there. 

 These stages are partially separated from the rest of the chamber by 

 woollen cloths. 



" While the goods are traversing these rollers, they are exposed to 

 heat and moisture, furnished to them by steam, which is made to issue 

 gently from three rows of trumpet-mouth openings. The temperature 

 is raised from SO deg. to 100 deg. or more — a wet-bulb thermometer in- 

 dicating at the same time 76 deg. to 96 deg., or always 4 deg. less than 

 the dry bulb thermometer. In this arrangement fifty pieces, of twenty 

 yards, are exposed at one time, and as each piece is a quarter of an hour 

 under the influence of the steam, 200 pieces pass through in an hour. 

 Although workpeople need scarcely ever enter the warmest part of this 

 chamber, a ventilator in the roof is opened when there is any consider- 

 able evolution of acetic acid. 



" The mordant, as already explained, does not become fully " aged " 



