266 Experiments on Indigo. 



state, and in its colourless soluble state too, capable of being 

 submitted to tests and processes, it becomes a matter of curious 

 interest to follow the changes of this singular substance, and 

 compare them with the theories formed in the laboratories at 

 home. 



It is, however, more than a mere matter of curiosity to set 

 on a sound basis the causes of the different manipulations, and 

 to examine the real effect of processes in which different 

 manufacturers have a diversity of practice ; — although it must 

 be confessed that, setting aside the difference of quality in the 

 plant, from season, care in its cultivation, soil, and other causes, 

 the business of the vats is so simple as to allow of little devia- 

 tion in practice or result. 



The most convenient manner of bringing before the reader 

 the various subjects of a short series of experiments which I 

 made this season, in conjunction with an intelligent friend 

 engaged in an indigo establishment, will be to incorporate them 

 with a relation of the general process of manufacture; but I 

 think it will save a good deal of repetition and explanation, to 

 give in the first place an epitome of what has already been writ- 

 ten on the subject ; that is, on the qualities and properties of 

 indigo itself, which have been elaborately examined by Berg- 

 man, Berthollet, Chevreul, Thompson, Crum, and latterly by 

 Berzelius. Their notices extend to minute details of the action 

 of every neutral salt, acid, and alkali of the chemical calendar ; 

 but the general results which are likely to be useful to the 

 manufacturer may be condensed into a very small space. 



Indigo is a definite vegetable product, which appears to 

 exist, in greater or less quantity, in a variety of plants, or 

 rather the elements of which it is composed are found in these 

 plants; for it is not until the juices of the vegetable begin to 

 act upon one another in fermentation, that indigo is developed. 

 It might at first be supposed that the green colour of plants 

 was connected with the presence of indigo ; but this is not the 

 case, as after the leaves have been steeped in the vats, they 

 retain entirely their original colour. 



When first dissolved from the plant, the indigo is in a colour- 

 less state, and is readily soluble in water ; but it becomes blue 

 on absorbing oxygen from the air, and appears then to have 



