i338.] 



Cultivation and Manufacture of Indigo, 201 



" Indig-o in the prepared stale is of a rich blue colour, which varies, 

 li(>\w\ ei , in its sliade in different specimens. When pure it is light 

 anH iVinMe; tasteh-ss, and ahno.t devoid of smell; of a smooth frac- 

 ture ; iii,s(dnhle m water or alcohol, but s >]uble in sulphuric and nitric 

 acids. Sotr.e varieties, >',uch as tlial known among the Spaniards b}' the 

 name u^l jUra, rs lighter than water; and the lightest is generally the 

 purest. Tin- analj'sis of M. Chevreul gives, as the composition of In- 

 diyo, a blue colouring principle called Indigotine, a red resin, a green- 

 i-.]i-red matie , united to the sub-carbonate of lime, alum, silica, oxyd 

 of iron, an(i sotne other salts. According to Dr. Ure, the ultimate con= 

 j fttiluen[S of pure Indigo blue, are — 



Carbon, 71-37 



Oxv^en, , 14-25 



Azofp, , 10-00 



H\drogen, 4*38 



100-00 



In(h*i>-o is frequently adulterated, by gummy, resinous, and earthy sub- 

 stances being added t<> it; and its weight and purity are also affected 

 by usin:-; lime in excels as a precipitant. Dr. Bancroft proposed, as a 

 test \<\ a>vceriMin the relative values of different specimens of Indigo, to 

 diss'dve equal portions of each in sulphuric acid, so as to fornm the 

 mixiiire known by Ihe name of liquid blue, and afier diluting with a 

 0. Main quantity of water, to compare the shades of colour possessed 

 by ihe sevt-ral mixtures. 



" indigo is the most vyluable and permanent of all the dye-stuffs. 

 It is also made u^e o! by painters in water-colours. 



" The metlu)d of preparing Indigo, and of applying it to the pur- 

 poses of dyeing, appear to !iave been very early known in India. Dr. 

 l3ancio!i* tins shown that the indicwn of Pliny (lib. xxxv. c. 6.) pos- 

 sessed hhiiiiar properties with the modern Indigo. It would appear, 

 by a passage in Cane})a lius, quoted by the same author, that, in the 

 15 h century, ihe Venetians were in the habit of receiving Indigo from 

 the East by the way of Alexandria. After the discovery of the pas- 

 sage to India by ihe Cape of Good Hope, the Dutch are supposed to 

 have been the first, about the middle of the IGtii century, to import it 

 direct into Europe. It was long, however, ere it came into general use 

 as a dve, and there appears to have existed against it a very unac- 

 j countable prejudice. It was considered to be a kind of stone, and was 

 ' prohibited in England during the reign of Queen Elizabeth, and also 

 in Saxony by the Elector, who described it in his edict as a corrosive 



* rhilosophy of Permanent Colours, vol. 1. p. 243. 



