THE INDIGENOUS DYES OF BENGAL. 163 



(IV). Fastness to Acid. 



Also determined as in case of cotton dyeings, i.e., samples were all steeped for 

 one hour in 10 per cent, acetic acid solution at 40°C, washed, dried and compared 

 with original. For i gm. of cloth 250 cc. of solution were used. The groups into 

 which the dyeings are classified are identical with the corresponding groups for cotton 

 dyeings. 



Conclusion. 



A summary of the results of the work recorded in this paper is given in Table V . 



The general result of the present work has been to show that the indigenous dyes 

 of Bengal are considerably more useful for dyeing on silk than for cotton dyeings, and 

 that the dyeings obtained are frequently considerably faster on silk than on cotton 

 This, taken in conjunction with the fact that many of the commonly used synthetic 

 dyes do not give at all fast dyeings on silk, causes the indigenous dyes to compare 

 much more favourably with their synthetic adversaries in this field than was the case 

 in the field of cotton-dyeing. The shades obtained from bakam on a tannin-iron 

 mordant, from manjista, from lac, kamala and jackwood may be said to have all-round 

 good fastness, as in no respect does any one of these dyeings come lower than III in 

 the scale. Thus of 10 dyestuffs examined, 5 have yielded dyeings which may be 

 characterised as all-round good. Of the 12 synthetic dyestuffs used for comparison only 

 4, viz., alizarine, primuline, chrysophenine and magdala red are capable of yielding 

 dyeings which may by the same criterion be similarly characterised. My work would 

 lead me to form a somewhat higher opinion of the value of kamala as a silk dye than 

 has been recorded by A. G. Perkin (Journ. Soc. Chem. Industry, XIV, 1895, p. 460). 

 The dyeings with lac proved to be faster to soaping even than the synthetic dyes which 

 were fastest in this respect. In fact the general fastness of lac dyeings made it ap- 

 pear to me a matter of surprise that this material has been so completely superseded 

 by synthetic dyes, the more so as it is necessarily obtained as a by-product in the puri- 

 fication of lac, a material for which there is an ever rapidly increasing demand. 



Finally it may be remarked that in the matter of brightness and cleanness of 

 shade the vegetable dyeings do not compare unfavourably with those obtained from 

 synthetic materials, nor is it any more troublesome to dye with the vegetable 

 materials than with those synthetic materials which yield the faster dyeings. 



It may be that I have attached more importance than is usual, when considering 

 silk dyes, to the fastness of the dyeings to washing and soaping ; but I can scarcely 

 imagine a dyeing which is very sensitive to washing to be altogether satisfactory for 

 any class of textiles. 



