754 



TEE AOBICVLTURAL JOURNAL. 



Indigoi. 



INDIGO MANUFACTURE. 



Suggestions by Professor Rudolf. 



THE following extract is taken from a 

 series of articles contributed to the 

 "Bulletin of Pharmacy," by Professor 

 Norman S. Rudolf, M.Sc, F.I.C. :— 



For the sake of clearness, it will be 

 well to divide the manufacture of indigo 

 into seven stages, as follows : — 



1. Steeping : The extraction of the in- 

 digo dye in the form of so.luble indigo, or 

 from the green plant (indican). 



3. Beating : The oxidation of the soluble 

 indigo (indican) by agitation of the solu- 

 tion and consequent precipitation of 

 indigo-blue. 



3. Settling : Allowing the precipitated 

 blue-indigo to fall to the bottom of the 

 vat. 



4. Boiling : Raising the magma of 

 indigo and water to such a temperature 

 as will destroy the ferment, and at the 

 same time cause it to filter readily. 



5. Filtering : The removal of the super- 

 fluous water, leaving the colouring matter 

 as a paste. 



6. Pressing : Compression of the paste 

 into large slabs. 



7. Preparation for the market : Catting 

 the slabs into cakes, stamping factory 

 mark, drying, brushing, and packing in 

 l^oxes. 



Steeping. — The indigo plant as it arrives 

 from the fields is packed carefully into 

 cisterns or "vats." These vats, which 

 have a capacity of from 1,000 to 2,000 

 cubic feet, are constructed of solid brick- 

 work, with a thin coating of Portland 

 cement, and are built in a range contain- 

 ing from fi.ve to twenty-five vats. Each 

 vat, after , filling with plant, is flooded 

 with water at ordinary temperature, the 

 mass of plant being prevented from rising 

 and swelling by bamboos with heavy logs 

 of timber placed across them and securely 

 fastened at either end l.y pins. The vat 

 is provided with an outlet so situated that 

 by it the whole of the water may be 

 drained ofl" ; this circular opening has 

 l)een previously closed by a large plug 

 of wood with hemp packing, or in some 



factories a kind of valve is in use. The 

 first effect of the addition of the water is 

 to cause all the animal and insect life 

 lodged among the plant to make its es- 

 cape from drowning, a circumstance 

 which not infrequently renders the close 

 observation of a newly filled vat an un- 

 pleasant task to the observer. During the 

 first hour or so the water has not much 

 effect upon the plant. The water extracts 

 a little chlorophyll, and a quantity of 

 l)ubbles come to the surface which analy- 

 sis has shown to consist of air and oxygen 

 gas, which is to be expected. From the 

 third to the seventh hour more chloro- 

 phyll is extracted and some indican goes 

 into solution. Towards the end of this 

 time the extrac<-ion of the latter proceeds 

 with great rapidity, the liquid turning 

 yellow. During this period a large evolu- 

 tion of gas takes place, and in consequence 

 of the bubbles becoming entangled in the 

 mass of plant the surface level rises a few 

 inches. Under favourable circumstances 

 the extraction should be complete, the 

 evolution of gas finished, and the surface 

 level of the vat commence to fall, about 

 the eleventh or twelfth hour of steeping. 



There are several simple methods in 

 use for deciding when the steeping_ pro- 

 cess has gone far enough. The liquid 

 should be of a golden brown colour ; the 

 surface undisturbed with thin film of in- 

 digo-blue appearing at the corners. On 

 agitation with a whisk of plant the foam 

 has a peculiar and characteristic appear- 

 ance. The gas which is evolved during 

 the process consists principally of a mix- 

 ture of marsh gas and hydrogen with a 

 little air, the bubbles exploding when 

 ignited. 



To determine the exact chemical re- 

 actions that underlie the steeping process 

 is not an easy matter. Various views are 

 held on the subject, but the point to de- 

 termine seems to be whether it is a case 

 of simple extraction, with an entirely in- 

 dependent fermentation taking place at 

 the same time, or whether the production 

 of the indigo is dependent upon the fer- 



