246 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



by means of bamboos, and heavy baulks of timber levered 

 down and fixed in position by horizontal pins, passing through 

 two uprights at each end of the vat. The vats containing the 

 pressed bundles are filled up with water and steeping is 

 continued over night, the liquor being allowed to run off into 

 lower vats in the morning. The hquor in the lower vats is 

 then thoroughly beaten up by men who stand immersed to 

 the hips in the hquor and beat it with bamboos shaped hke 

 oars, or artificial beaters of various kinds are used. The 

 object of this process is to bring the hquor thoroughly in con- 

 tact with air when the indigo is precipitated. The progress 

 of the operation is tested by the manager by inspection of 

 small portions of the hquor from time to time. 



On completion of the beating process, the indigo is allowed 

 to deposit, the hquid run off to waste, and the wet indigo 

 mud run on to draining cloths. When it has attained a 

 suitable consistency, portions are wrapped in cloth and pressed 

 hke cheeses in a press ; the pressed mass is then cut into 

 cakes and finally dried. 



The impetus towards improvement of this process has 

 been due to the acute competition during recent years of 

 artificial indigo, the extent of which may be gathered from 

 the fact that in 1896, out of a total weight of 46,683 cwts. of 

 indigo imported into Great Britain, only 7,641 cwts. consisted 

 of the natural product. 



In 1902 Mr. W. Popplewell Bloxam and his colleagues 

 began their researches for the Government of Bengal. The 

 work was carried on in India for two years and was afterwards 

 continued from 1905 to 1907 in the University of Leeds, under 

 the general supervision of Mr. A. G. Perkin, F.E.S. 



A report of this work was published in 1908 by the Govern- 

 ment of India, and the following information is mainly taken 

 from its pages. 



In the first place it should be explained that the pure 

 colouring matter of indigo is indigotin, which has the molecular 



