TEE AGBICULT 



URAL JOURNAL. 



755 



mentatiou. For several reasons the writer 

 is inclined to think that the first theory 

 is nearest to the truth, for a small 

 quantity of bruised plant gives up 

 its colouring matter in half an 

 hour or so when steeped in water 

 at ordinary temperature ; agaiu, with hot 

 water (140''F.) the extraction on a labora- 

 tory scale is a matter of a few minutes. 

 These facts militate against the theory of 

 the indigo being obtained by a fermenta- 

 tion process. The fact, however, of the 

 fermentation and evolution of gas coming 

 to an end about the time when the whole 

 of the colouring matter is extracted 

 appears to be more than a mere coin- 

 cidence. The addition of antiseptics to 

 the vat causes the fermentation to be 

 much less violent, but this may simply 

 mean that the ordinary rapid decay which 

 takes place in a wet mass of plant in. the 

 tropics is prevented. 



A great many attempts have been made 

 and a number of processes patented for 

 the improvement of the yield and quality 

 of the dye by the addition of chemicals 

 to the steeping- vats : among others may 

 be mentioned ammonia and its salts, 

 potassium nitrate, sodium nitrate, lime, 

 carbolic acid, and other germicides, acids, 

 and alkalies. The majority of these 

 additions have been made in a haphazard 

 manner, as a rule doing more harm than 

 good ; the use of carbolic acid is thought 

 by some to improve the quality of the 

 product. 



It will now be well to consider what it 

 is that causes the yield of indigo practi- 

 cally obtained to fall so far below the 

 quantity which can be obtained from the 

 plant in a laboratory experiment. The 

 principal loss appears to be in the deposi- 

 tion of indigotin in the plant cells, and 

 from the liquid in the steeping-vat a 

 further small quantity is probably de- 

 stroyed by putrid ferments. As already 

 mentioned, a solution of indican deposits 

 indigotin slowly at ordinary temperature 

 — at the temperature of the steeping-vat 

 (85'='F. to 95°F.). The amounts thus de- 

 posited during the time of steeping (some 

 twelve hours) must be considerable, and 

 the writer has made a series of experi- 

 ments to determine whether it is not 

 possible to prevent this decomposition of 

 indican taking place and avoid a serious 

 loss. It was found that a solution of in- 

 dican is practically permanent at a tem- 



perature below 400 F., provided the 

 liquid is not unnecessarily exposed to the 

 air. The expei'iment was several times 

 repeated of steeping the plant in a small 

 vat with water maintained at about this 

 temperature by additions of ice. The 

 effect of this cooling was very marked : 

 the extraction was slow, requiring some 

 sixteen to eighteen hours for its comple- 

 tion ; the liquid was clear, bright, and of 

 a fine greenish-yellow colour ; a very 

 slight amount of fermentation seemed to 

 take place, and the evolution of gas was 

 small. The yield was pei-ceptibly im- 

 proved, the average being about 20 per 

 cent, increase, and the quality of the re- 

 sulting indigo all that could be desired, 

 the extracted plant being of a much 

 lighter colour than usual. The writer 

 found that the figure obtained by adding 

 the amount of indigo ar. found in the re- 

 sidual extracted plant to the amount ob- 

 tained by the extracting process was 

 practically a constant for thei same class 

 of plant When iced water was used the 

 amount of indigo obtained increased, but 

 a smaller quantity remained in the ex- 

 tracted plant than when water at ordinary 

 temperatures was employed. These figures 

 were necessarily only approximate, as the 

 calculation of the mass of plant is 

 difficult and leads to error. This process 

 has not been tried on a large scale owing 

 to the expense and difficulty of importing 

 the necessary freezing machinery, and of 

 the inconvenient length of time which 

 would be required for the extraction of 

 an ordinary vat of indigo ; this time, 

 however, might undoubtedly be greatly 

 shortened if the plant was crushed or 

 bruised beforehand, provided this would 

 not lower the yield. The quality of the 

 water used for steeping affects the quality 

 of the dye very materially, and the yield 

 seems to be slightly influenced. The 

 water most suitable for use is clear, free 

 from finely suspended inorganic matter, 

 and containing from five to ten parts per 

 100,000 of calcium carbonate. A water 

 rendered turbid by finely divided inor- 

 ganic matter held in suspension is not 

 necessarily unsuitable for use, as the mud 

 settles on the plant during the steeping 

 process and remains there ; but there is 

 a variety of very finely divided slimy 

 clay, Avhich, although it does not cause 

 the water to appear very turbid, neverthe- 

 less yields a bad coloured and heavy lin- 



