Dr. Ure on Indigo. l6l 



cultivated in the East Indies, produces the best indigo ; but 

 others extol the indigofera anil, the ind. argentea, the ind. di- 

 sperma, which yields the Guatimala kind, and some the Mexi- 

 cana. About sixty species of the indigofera are at present 

 known, but those above named are in peculiar esteem. My 

 object in staling these differences here is chiefly to shew that 

 u drug obtained from such a variety of vegetable species must 

 necessarily vary in composition. The matter which affords the 

 indigo is confined entirely to the "pellicle of the leaves, and 

 exists in largest quantity at the commencement of maturation, 

 while the plant is in flower ; at a somewhat later period the 

 indigo product is more beautiful but less abundant; after- 

 wards, much less of it is obtained, and of a worse quality. 

 The plant is remarkable for giving a blue tinge to the urine 

 and milk of cows that feed upon its leaves ; a circumstance 

 which accords with the known permanence of the dye. The 

 statement of Mr. Weston, in this Journal (No. XXVII. p. 296), 

 agrees with these observations on the ripening of the blue 

 principle. He shews that the developement of this matter in 

 the indigo/eras goes on in the leaves, even after they are sepa- 

 rated from the plant and dried. When packed up for a few 

 weeks, more or less according to their preceding state of ripe- 

 ness, the leaves assume a light lead colour, which gradually 

 deepens into a blackish hue. The planter studies to seize the 

 period at which the maximum portion of colouring matter is 

 formed, that he may then transfer the leaves to the steeping 

 vat. 



Three different processes are employed for extracting the 

 indigo, each of which must modify more or less the nature of 

 the product. In the first and second, the dried leaves are 

 operated on ; in the third, the recent plant. For the perfect 

 success of the two former processes, the plant should be very 

 speedily deprived of its water of vegetation ; hence the indigo- 

 fera is reaped only in fair weather. An hour and a half before 

 sunset, the plants are cut down, carried off the field in bundles 

 and immediately spread on a dry floor. Next morning, at six . 

 o'clock, the reaping is resumed for an hour and a half before 

 the sun acts too powerfully on vegetation, and the plants are 

 treated in the same way. Both cuttings become sufiiciently 



JAN. — MARCH, 1830. M 



