Practical Magazine 14, 1876
(Chemistry applied to the Arts, Manufactures, &c.
Dyeing, Calico Printing, Bleaching, Tanning, and Allied Subjects.)
Plants which produce this colouring matter are plunged in vats till the water has deprived them of it to a great extent, and the liquid is then evaporated to obtain the indigo. A pretty high temperature is necessary during this steeping; but hitherto no use has been made of artificial heat, as it has been thought that the temperature of the surrounding air, which is generally high in the countries where this industry is carried on, is sufficient for the purpose.
Mr. OLPHERTs has tried the use of steam, and the results of his experiments in India, with rather rude apparatus, appear to warrant the change. The temperature of the water in the rainy season varies from 92° to 95° Fahr. In the vats it has been raised to 111°, and, in spite of the difficulties attending the new process, an increase of produce has been obtained of about 25 per cent. in comparison with plants of the same crop, steeped in the same vats, the same day, and for the same length of time.
Heat has also been applied during the beating, and good results have been obtained without injuring the colour or quantities of the indigo. Moreover, a fresh steeping for forty hours of plants treated with artificial heat gave no indigo, while those subjected to the ordinary process still retained some.
- Technologiste
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