Calico Dyeing. 381 



the calico over copper cylinders, which are heated by the 

 vapour of water, or, what is better, by spreading it out on a 

 very hot drying-stove, between wooden cylinders, until it 

 is dried. 



Calico which is impregnated with the acetate of alumina 

 mordant, should be hung up in an airy place for six or 

 eight days. More acetic acid is disengaged in this case, 

 and the colours become more saturated. 



When many pieces hang in one place where there is no 

 current of air, the disengaged acetic acid will prove injurious 

 to the mordant ; it is, therefore, necessary to obtain a change 

 of air by proper ventilation. It is still a better plan to sa- 

 turate the acetic acid by disengaging ammoniacal gas. This 

 will, in most cases, however, be too expensive. 



Calico dyeing. — During the dyeing, the mordanted calico 

 (as has been stated under water) has to overcome the dis- 

 solving power of the water, in order to abstract the colour- 

 ing matter from it. This is effected generally incompletely, 

 so that the solution, even when the calico to be dyed is so 

 considerable that it can only be half-saturated, still retains 

 some colouring matter. This can only be taken up by 

 boiling with fresh mordanted calico ; yet still some colour- 

 ing matter often remains, which can only be exhausted by 

 a third piece of cotton. 



This remarkable property depends on the circumstance, 

 that the dye contains many colouring matters which are 

 not equally taken up by the calico. In this case, one after 

 the other combines with the mordanted calico. This hap- 

 pens particularly with madder. If, in a solution which 

 contains 4 loths (1-187 oz.) of madder, calico mordanted 

 with the alum mordant, No. 1, be dyed three times in suc- 

 cession, the cotton in the first dyeing will be dark-red, 

 from the madder-red ; on the other hand, that of the third 

 dyeing will be yellowish-red, from madder-yellow. The 

 calico from the second dyeing possesses an intermediate 

 colour. 



If the same experiment is made with 4 loths (1-872 oz.) 

 of quercitron and mordanted calico, a similar result is 

 obtained. The pieces of calico which were dyed in succes- 

 sion come out at first dark-yellow, from the solution ; they 

 amount to 14 loths (6-55 oz.) A dark-yellow is no longer 



