Macfadyen*s Flora of Jamaica. 267 



<* A beautiful yellow precipitate may be obtained, by means of 

 acetate of lead, from the Madeira-coloured liquid, drawn off in the 

 beating vat. This is said, by Mr. Weston, to promise to supply a 

 great desideratum — a permanent yellow dye. Experiments are, 

 however, wanting to confirm this. 



<'. Indigo in the prepared state is of a rich blue colour, which varies, 

 however, in its shade in different specimens. When pure it is light 

 and friable ; tasteless, and almost devoid of smell ; of a smooth frac- 

 ture; insoluble in water or alcohol, but soluble in sulphuric and ni- 

 tric acids. Some varieties, such as that known among the Spaniards 

 by the name o\\flora, is lighter than water ; and the lightest is gene- 

 rally the purest. The analysis of M. Chevreul gives, as the com- 

 position of Indigo, a blue colouring principle called Indigotine, a 

 red resin, a greenish-red matter, united to the sub-carbonate of lime, 

 alum, silica, oxyd of iron, and some other salts. According to Dr. 

 Ure, the ultimate constituents of pure Indigo-bluey are — 



- Carbon, 71-37 



Oxygen, 14'*25 



Azote, 10-00 



Hydrogen, 4*38 



lOO'OO 

 Indigo is frequently adulterated, by gummy, resinous, and earthy 

 substances being added to it ; and its weight and purity are also af- 

 fected by using lime in excess as a precipitant. Dr. Bancroft pro- 

 posed, as a test to ascertain the relative values of different specimens 

 of Indigo, to dissolve equal portions of each in sulphuric acid, so as 

 to form the mixture known by the name of liquid blue^ and after di- 

 luting with a certain quantity of water, to compare the shades of co- 

 lour possessed by the several mixtures. 



"Indigo is the most valuable and permanent of all the dye-stuffs. 

 It is also made use of by painters in water-colours. 



** The method of preparing Indigo, and of applying it to the pur- 

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

 Bancroft* has shown that the indicum of Pliny(lib. xxxv. c. 6.)pos- 

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

 by a passage in Caneparius, quoted by the same author, that, in the 

 15th century, the Venetians were in the habit of receiving Indigo 

 from the East by the way of Alexandria. After the discovery of 

 the passage to India by the Cape of Good Hope, the Dutch are 

 supposed to have been the first, about the middle of the 1 6th cen- 

 tury, to import it direct into Europe. It was long, however, ere it 

 came into general use as a dye, and there appears to have existed 

 against it a very unaccountable 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 de- 

 scribed it in his edict as a corrosive substance, and fit food only for 

 the devil. Soon after this its importance came to be understood, 

 and the cultivation of the plants which yield it was introduced into 



* Philosophy of Permanent Colours, vol. i. p. 242. 



