Experiments on Indigo. 273 



the vats did not present any satisfactory results ; the mean 

 temperature was about 85 degrees Fahrenheit. 



" The fermented liquid is drained off into inferior vats, which 

 are called the ■ beating vats.' " 



At the time when the vat is opened, the liquid is found by 

 experiment to have a specific gravity (at the surface) of .1001.5, 

 and at the bottom of the vat, 1003.1. The leaves appear to 

 have lost nothing, being as green and fresh as when they were 

 first strewed in the vat. By carefully weighing a portion of 

 leaves, however, before immersion, and washing and drying 

 them in the air after it, they were found to have lost more than 

 three quarters of their weight: of this loss the greater part was 

 water, which they apparently cease to have the power of retain- 

 ing when the soluble juices have been withdrawn. The solid 

 matter taken up by the vat amounts to between J 2 and 14 

 per cent, of the weight of the leaves. 



When the fermented liquid runs off into the lower vat, a frothy 

 extrication of gas covers the whole of its surface. It is a good 

 sign if the froth, in subsiding, assumes a rosy tint, which is in 

 fact nothing more than a very thin film of indigo, and it proves 

 that the deposition is ready to take place. 



" In this vat the liquid undergoes a beating for about two 

 hours — it is continually stirred about and agitated by a number 

 of men, either with their arms or with a sort of short oar." 



The object of this operation appears to be threefold. In 

 the first place, the agitation extricates a large proportion of 

 the carbonic acid gas which still remains combined with the 

 liquid : — in the second, it exposes fresh surfaces continually to 

 the contact of the air, whence the oxygen is rapidly seized by 

 the nascent indigogene : — and thirdly, it coagulates the fecula 

 of the indigo in larger grains, so as to render it more easily 

 precipitable. 



By way of understanding more clearly what takes place in 

 the beating vat, a number of bottles were at different times 

 carefully filled with the yellow liquor, just as it was ready 

 to be drawn off from the upper vat, for experiments in the 

 laboratory. 



Neither keeping, boiling, the addition of acids or alkalies, 

 nor even putrefaction, appeared materially to affect the power 



