654 



CALICO-PRINTING 



The arrangement of moveable square wooden rollers is to allow of the roll of pieces 

 placed upon these rollers being occasionally turned part round, so that they may bo 

 uniformly steamed, which would not bo the case if the same part were always resting 

 on the wooden roller. 



Colours fixed by steaming are either pigments insoluble in water, cemented to the 

 cloth by the coagulation of the albumen or other nitrogenous vehicle with which they 

 are mixed, or, as in the case of aniline colours, this coagulum becomes itself a mordant 

 and at the time of coagulation and adherence to the fibre carries with it the colour in 

 chemical union; or, as in the case of dyewood and cochineal colours, these may bo 

 described as coloured lakes temporarily held in solution by acids, and during the 

 steaming, the cloth gradually withdraws these lakes from solution, the acid being 

 either dissipated or so modified as to be incapable of holding the lakes dissolved. The 

 state of the steam is an important matter. It is not the heat alone that produces the 

 effect ; for it may easily bo demonstrated that heating cloth, when printed and dried, 

 has no effect whatever. The steam, to be effective, must be as saturated with mois- 

 ture as possible, and for this reason the steaming apparatus should never bo near the 

 boiler : it is no disadvantage for the steam to travel a considerable distance before 



being applied. In some print-works the steam is made to pass through water in a 

 vessel placed below the steam-chest, so that it arrives in the chest perfectly saturated 

 with water. At the same time, the steam must not be of so low tension as to cause a 

 deposit of moisture on the pieces, -which would be very injurious, by causing the 

 colours to run or mix. Steam-blue depends for its fixation on the decomposition of 

 ferrocyanic acid by the high temperature and presence of vapour of water into white 

 insoluble ferrocyanide of iron and potassium, -which, by acquiring oxygen from the 

 air or during the washing-off, becomes Prussian blue. The shade of it is much 

 modified by the oxide of tin in the cloth and the prussiate of tin that forms part of 

 the colour. It appears that tin substitutes iron, forming a compound ferrocyanide of 

 tin and iron, or a ferro-stanno-cyanide of iron, which is of a deep violet-blue colour. 

 Greens are mixtures of yellow lakes with the Prussian blue, formed by decomposition. 

 In both- these colours there is a large quantity of hydrocyanic acid disengaged 

 during the steaming ; steam being decomposed, its hydrogen going to form hydrocyanic 

 acid. 



Madder-extract and alizarine colours require more care in steaming than ordinary 

 dyewood colours. The steam-chest should be fitted with a manometer to indicate the 

 pressure of the steam inside the chest. The steam at first should only be about 3 Ibs. 



