Nov., 1904.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



^55 



liquor is run into tlie beating vat I>. The 1)catcr.s OM 

 arc held by tlie wooden fork X. C is tlie precipitating 

 tank witii the stops L, which are used for entering the 

 vat to clean or empty it. Q is the outlet for the 

 supernatant liquor. P is the well from which the water 

 is obtained with the trough ("iG leading into the fer- 

 menting vat. \' is the drying house in which the 

 staging for placing the indigo is shown at t. 



It has already been stated that the indigo is not 

 found in the free state in the plant itself, but in the 

 form of a g/iicosii/r called indiain, which must be 

 split up in order to obtain the indigo. This spilling up 

 process is supposed to take place during the fermenta- 

 tion, but by the fermentation the indigo blue is not 

 directly formed, a jjroduct called indigo white being 

 produced. Xow indigo itsi'lf is not a soluble substance, 

 but indigo white is, and can be obtained from indigo 

 blue by taking away part of its oxygen. When, then, 

 this solution of indigo white is run into the beating 

 vat and agitated, air becomes mixed with it, and from 

 this it takes up oxygen, becoming converted into (he 

 insoluble indigo which is precipitated out. 



As indigo blue or indigotin is insoluble in water, it 

 follows that it cannot be used directly as a dye without 

 being first made soluble. In order to dye with indigo 

 it is first converted into indigo white by means of re- 

 ducing substances — that is, substances which will take 

 away a portion of its oxygen. It is to aid in the 

 formation of indigo white that woad is .iddcd to the 

 vat, because it helps to set up a certain kind of fer- 

 mentation (butyric f rmentation). .'\ typical woad vat 

 contains from 20 to :;5 lbs. indigo, from li to 5 cwt. 

 woad, 20 lbs. bran or flour, 5 to 20 lbs. madder, and 

 24 lbs. slaked lime. The precautions necessary in 

 preparing the vat cannot be entered into, but the 

 operator must be skilful and experienced, the 

 art of preparing the bath often being handed down from 

 father to son.* When the vat is ready, which usually 

 takes from two to three days, the wool or other goods 

 are moved through the licjuid for from 20 minutes to 

 over an hour by means of a machine called a " hawk- 

 ing machine," they are then taken out of the vat and 

 exposed to air, by which means the indigo white be- 

 comes oxidised to indigo blue. 



Indigo blue is one of the fastest if not the fastest of 

 blue dyes, and it is extremely stable to light and wash- 

 ing. The only fault it has is that it is apt to rub — that 

 is, to colour other substances blue which are in contact 

 with it, e.g., the linings of dresses, Kc. Very many 

 attempts have been made to substitute other dyes in 

 place of indigo, but it has always succeeded in holding 

 its own, most other dves lacking the rich hv..' and 

 bronzy appearance produced by indigo. 



A few years ago the Indian indigo manufacturers 

 woke up with a start and found that there was an 

 artificial indigo on the market — that is, an article 

 which was made entirely by chemical means, and which 

 was not dependent upon the growth of a plant. This 

 artificial or synthetical indigo is made from products 

 obtained from coal-tar and has exactly the same con- 

 stitution and properties as the product produced from 

 the indigo plant. 



The manufacture of synthetical indigo is one cf the 

 greatest triumphs of chemical science. For more than 

 20 years German chemists had been engaged upon the 



* It must, of course, be understood that there are a great \ arietv 

 of methods employed in preparing an indigo bath .different ba'hs 

 being required for different kinds of work. 



problem of how to prepare indigo on a manufai-turing 

 scale. I'rofes^c.r \()n l>ai-\er had .-ilready in 1S7S 

 discovered wh:it tlu constitution of indigo was, and 

 had been able to prepare it in small quantities in the 

 laboratory. But the problem of how to make it in 

 quantity and cheaply toolc more than 20 years to 

 elucidate, and the expenditure of enorinous sums of 

 money. Chemists all the world over were aware of 

 the facts, but the indigo j^lanters with a sublime in- 

 difference, unmindful of the fact that the great madder 

 industry, and the manufacture of alizarine from this 

 plant, had been abandoned owing to the advent of the 

 coal-tar colour industry, went their w;iy, Ire.-iding in 

 the old unscientific foofsti-ps ol Iheii' forelal hers - we 

 had almost said of the ancient I'^i^yptians — until tliey 

 were startled, as one of them pictures(|uely said, " hy a 

 l)olt from the bhie." Svntlietical indigo was a 

 realitv. 



.\s might be expected, there is a great deal of con- 

 troversy as to the rival merits of natural and syntheti- 

 cal indigo. As ,1 mailer of fiict, indigotni, the bhie 

 c ;louring principal of indigo, w hether synthetically 

 prepared or obtained from the plant, is exactly the 

 same substance. But the indigo obtained from the 

 plant is not pure, as it contains besides other impiu-i- 

 lii-s small (|uantilies of indigo red, indigo brown, 

 ,infl a gummy substrmce Called indigo-gluten, .-nid 

 the presence of these is said to impart a finer tone 

 to the dyed articles. On the other hand synthetical 

 indigo is quite pure, and the quality is always the same. 

 The methods of the indigo planters have been un- 

 scientific in the extreme ; now that the horse has been 

 stolen they are Ircking the stable-door and have called 

 in scientific adviix'. lm[)rovements in the manufacture 

 and better agricultural methods may, and probably will, 

 postpone the final triumph of the synthetical indigo ; 

 but it is to be feared that this once flourishing industry 

 will shortly be a thing of the past. It must be admitted 

 that during the list six of seven years, since the intro- 

 duction of synthetical indigo, the weather conditions 

 have made it very difficult for the planters to obtain 

 good crops, but even taking this into account the 

 following figures, taken from a recent issue of The 

 Times, are striking in the extreme. In 1894-5; there 

 were 1,688,042 acres under cultivation for indigo ; in 

 1502-3 the acreage had sunk to 574,654 ; the output of 

 indigo had during the same period fallen from 237,494 

 cwt. to 73,908 cwt. For the five years, 1899 to igoo, 

 the average export of indigo was 148,000 cwt. in 

 1903-4 it sank to 60,410 cwt., and the average price 

 from 203 rupees for the iimiiiid (Sj Uis.) to 14S 

 rupees. 



A good deal of the land, at one time under culti\a- 

 tion for indigo, is now being planted with sugar, and 

 it is a matter of gre;it importance for India that as the 

 indigo is gradually forced out — we trust that the pro- 

 cess may be a slow one — its place should be taken by 

 some new product. 



The subject of indigo cultivation and manufacture 

 has been brought before readers of " Kxowi.eooe " in 

 f)r(ler to bring home the absolute importance of scientific 

 knowledge and scientific researcli. If the Indian 

 inanufacturcrs had at the first sign of the appearance 

 (jf synthetical indigo, in 1878, exerted themselves to 

 understand the scientific problems underlying the pro- 

 ductif)n of indigo from the plant, we might not to-day 

 see a waning industry. One has only to look at the 

 wonderful progress of the beet sugar industry to see 

 what can be done when chemical and agricultural im- 

 provements are carried on side by side. 



