July 30, 1908] 



NA TURE 



297 



The results achieved down to that period were duly 

 reported upon, and the report published by the Govern- 

 ment of Bengal in 1905. Mr. Bloxam also gave an 

 account of his work to the Chemical Society in 1904, 

 and this was published by the Society in the 1905 

 volume of its Transactions. In the summer of 

 1905 the Government of India, through the India 

 Office, authorised the continuation of the researches 

 on indigo by Mr. Blo.xam. The Clothworkers' Re- 

 search Laboratory of the University of Leeds was 

 appropriately chosen for the work, and the latter was 

 placed under the general superintendence of Mr. 

 -A. G. Perkin, whose special familiarity with the 

 chemistry of natural colouring matters is sufficiently 

 well known to command full confidence in any results 

 to which his name is attached. 



So much by way of historical introduction. The 

 report now before us is the outcome of the work 

 carried on at Leeds by Mr. Bloxam and his colleagues 

 from the summer of 1905 down to the end of last 

 year. A careful consideration of the contents of this 

 little official volume of about 117 pages \v\\\ satisfy 

 .■my impartial reader who is interested in the subject 

 that the Indian Government has been well advised 

 in the interests of a languishing native industry in 

 authorising the continuation of the researches. The 

 only point that arises, in fact, from the results so 

 far obtained is whether the official authorisation of 

 the vi'ork has not been prematurely brought to a 

 close. The problems that have had to be worked out 

 at Leeds are by no means simple — they were sur- 

 rounded by e.xperimental difficulties, and in spite of 

 the very large amount of work carried out by the 

 author and his colleagues, there still remain many 

 questions of vital importance to the prospects of 

 survival of natural indigo to which answers are ur- 

 gently needed. To mention one only — why has it 

 not hitherto been found possible to obtain from pure 

 indican, the glucoside of indoxyl, a theoretical yield 

 of indigotin by enzyme action or by chemical methods? 

 It is probable that, under the conditions of manu- 

 facture, the indoxyl at the time of liberation, in- 

 stead of condensing wholly to indigotin, gives rise 

 to some secondary products (? indirubin and in- 

 digo brown) which, from a tinctorial point of view, 

 represent so much loss of valuable material. If this 

 secondary reaction could be converted into the indi- 

 gotin condensation it might make an enormous differ- 

 ence in the struggle between natural and synthetic 

 indigo. It is satisfactory to learn from the report 

 that this point will be further investigated at Leeds. 



The various papers published by Mr. Bloxam and 

 his colleagues in the scientific and technical journals 

 during the two years specified are re-printed in the 

 present report, so that the case may be regarded as 

 now presented in the order of its development. Sec- 

 tion iii. is devoted to a consideration of the results 

 of analysis of the indigo obtained from the " Mahai " 

 of the plant grown on the experimental plots at the 

 Dalsingh Serai Research Station during the season 

 1903. It is of interest to read, in connection with 

 these results, the following passage : — " .So to the 

 author's extreme regret these expensive and laborious 

 experiments result in inability to draw anv exact 

 conclusions as to the influence of the various manures 

 — the results being completely obscured by the faulty 

 and irregular nature of the ' Mahai ' " (p. 98). 



At the outset of his investigations the author de- 

 cided, and we think wisely, that " before being certain 

 of the efficiency of the inanufncturing process, or of 

 being able to suggest any valid improvement of it — 

 two factors were necessary, fa) An accurate process 

 for the estimation of the finished product fair-dried 

 cake). f&) \r\ accurate knowledge of the amount of 



NO. 2022, VOL. 7SI 



colour which could be obtained theoretically from the 

 manufacture, i.e. an accurate knowledge of the in- 

 digotin content of the green leaf." This extract 

 furnishes the key to the whole of the subsequent work. 

 It is now generally well known that a dependable 

 analytical method for estimating indigotin has been 

 worked out, and a very satisfactory process devised 

 for estimating the indican in indigo-yielding plants. 

 It is not necessary in these columns to enter into 

 controversial points or into the minutias of analytical 

 procedure. The merits of the " tetrasulphonate " 

 method are sufficiently known to those who have used 

 it or have seen it applied. Its accuracy is vouched 

 for in an appendi.x to the present report by many 

 well-known chemists who have given independent 

 opinions — notably Prof. Norman Collie, Mr. A. C. 

 Chapman, Prof. W. H. Perkin, and Prof. A. G. 

 Green. As regards the beautiful application of 

 V. Baeyer's synthesis of indirubin from isatin and 

 indoxyl. suggested in the first place by Beijerinck as 

 a suitable method for estimating indican, there was 

 possibly a loophole for criticism in view of the most 

 important fact that this method gives a higher result 

 than any other known process for determining the 

 quantity of indican in the leaf. It might have been 

 fairly urged that in the leaf extract there might be 

 contained substances other than indoxyl w-hich, under 

 the conditions of the analytical process, combine with 

 isatin to give an insoluble compound which comes 

 down with the indirubin and so adds to the weight 

 of the dry precipitate. The answer to this objection 

 is virtually contained in the present report, from 

 which it appears that the indirubin obtained in the 

 estimations is, as shown by ultimate analysis, a pure 

 compound. But in order to get further assurance on 

 this vital point, further experiments have, at the 

 writer's request, been carried out at Leeds with the 

 extract of the dried leaf of Tc[>hrosia purpurea, in 

 which not a trace of indican was found bv the isatin 

 method, the precipitate obtained being completely 

 soluble in alkali. Special interest attaches to the 

 selection of this plant because it is reputed to be 

 indigo-yielding in a living state. 



If it be now asked how, after this later work, 

 stands the case for the indigo-planter, it must be con- 

 ceded that if the results obtained by Mr. Bloxam and 

 his colleagues are correct — and the present writer sees 

 no reason for doubting their accuracy — there is yet hope 

 for a considerable amelioration of the manufacturing 

 process. The introduction of exact analytical methods 

 has enabled the authors of this report to show that 

 the older methods have overestimated the indigotin 

 content of the dried " cake," and have under- 

 estimated the amount of indican in the leaf. If there 

 is considerablv more indican in the leaf than is 

 accounted for bv the present manufacturinsr process, 

 there is assuredly scooe for the further investigation 

 of this process in the field. It may be a losintr s^ame ; 

 the " isatin method " mav indicate results which are 

 unrealisable in the factory. But these results are 

 surely worth trvins' for in view of the enormous im- 

 portance of the indigo cultivation to our Indian 

 Empire. Even if the whole amount of indican in the 

 plant cannot be made to yield the theoretical Quan- 

 tity of indigotin, there is still margin for such an 

 improvement in the manufacture of nlant indigo as 

 to enable the latter at least to survive in face of the 

 competition from the chemical manufacturers. Nor 

 must it be for.n'otten that the Indian industry has a 

 biological as well as a chemical side. The question was 

 raised bv the writer in inoi whether there might not 

 be plants suitable for cultivation in India containing 

 a larp-er ounntitv of indican than those now made 

 use of (/. sumatrana and /. arrecta). The answer is 



