250 
CALYC1FJLOHZE. 
formed, which are subsequently divided into smaller cakes, 
and allowed to dry gradually in the shade. 
The boiling process, although not generally adopted, is said 
to improve very considerably the quality, and enhance the value 
of the produce. 
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. Ex- 
periments 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 fracture : insoluble in water or alcohol, but 
soluble in sulphuric and nitric acids. Some varieties, such as 
that known among the Spaniards by the name of flora, is 
lighter than water ; and the lightest is generally the purest. 
The analysis of M. Chevreul gives, as the composition of In- 
digo, 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 
ultimate constituents of pure Indiqo-blue, are^ 
Carbon, - 
- 
71.37 
Oxygen, 
- 
14.25 
Azote, 
- 
10.00 
Hydrogen, 
- 
4.38 
100.00 
Indigoisfrequently adulterated, by gummy, resinous, and earthy 
substances being added to it ; and its weight and purity are 
also affected by using lime in excess as a precipitant. Dr 
Bancroft proposed, 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 diluting with a certain quan- 
tity of water, to compare the shades of colour 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. 
rhe method of preparing Indigo, and of applying it to the 
purposes of dyeing, appear to have been very early known in 
India. Dr Bancroft* lias shown that the indicum of Pliny 
(lib. xxxv. o. 6.) possessed similar properties with the modern 
Indigo. It would appear, by a passage in Capenarius, 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 
• Philosophy of Permanent Colours, vol. i. p. 242 . 
