130 SCIENTIFIC REPORTS OF THE AGRICULTURAL RESEARCH 



culture and that of the steeping water, or even to the pre- 

 sence of unfavourable chemical conditions in the latter, and 

 further work must be done to find out how to secure the 

 most favourable conditions for the multiplication and 

 activity of the artificially introduced bacteria. In other 

 industries depending upon controlled bacterial fermenta- 

 tion the use of sterilized raw material is generally adopted; 

 this would seem to imply that the absence of other bacteria 

 is a condition of success for the employment of pure cul- 

 tures, but it does not necessarily follow. in the case of indigo. 

 Here we have in the ordinary factory working frequent 

 cases of losses of the order of 30 — 40 per cent, due largely 

 to imperfect hydrolysis, partly as a consequence of the 

 absence of the proper bacteria and partly to the presence 

 of abnormal numbers of destructive species. It appears 

 probable from the past season's experience that by sedi- 

 mentation and the introduction of .sufficient amounts of 

 vigorous cultures of the proper species it should be possible 

 to alter the character of the fermentation in the steeping 

 vat so as to secure more complete hydrolysis, })ut a consider- 

 able amount of work must be done before it is possible to 

 elaborate a routine method suitable for use in a factory 

 without immediate scientific control. 



Hot water extraction. In the report for the previous 

 year (1916-17) reference was made to the use of hot water 

 extraction as a means of eliminating undesirable bacteria; 

 a further advantage of such a method would be to secure a 

 higher percentage of extraction of the indican in the plant; 

 the Indigo Research Chemist has shown that imperfect 

 extraction in many cases leads to a loss of 30—40 per cent, 

 in ordinary factory working, and if hot water extraction 

 could be successfully adapted to factory conditions, it should 

 be possible to obtain a liquor not only comparatively free 

 from bacteria (although of course not absolutely sterile) but 

 containing a much higher percentage of the indican present 

 in the plant from which it was derived. 



With a view to obtaining information as to the possi- 

 bilities of this method a hot water extraction vat was added 



