306 CHYMISTRY APPLIED TO AGRICULTURE. 



may serve to deepen dyes, made of the cakes, for obtaining 

 light blues. M. Pariolati, dyer at Quiers, has found this an 

 excellent article for giving a fine blue to silks. But it can be 

 employed only when the dye-house is in the neighbourhood 

 of the indigo manufactory. 



The leaves may also be bruised after having had the two 

 first waters passed through them, and be formed into cakes 

 in the usual manner. These cakes will not be of the first 

 quality, but they are useful as a fermentable substance, and 

 produce in this way the same effect upon the woad dye 

 which is prepared for coloring. This has been proved by 

 experiments conducted upon a large scale, and these cakes 

 are in demand at a price one third less than those made 

 from leaves containing all the indigo. 



The process which I have described for obtaining indigo 

 by a hot infusion, is more simple than any other mode. 

 But as the indigo is more or less formed or oxidated in the 

 leaves, according to the period of their vegetation, it is not 

 at all times equally soluble, and especially when it is (as in 

 leaves that have passed their maturity) in the state of black- 

 ish blue. It is therefore necessary, when this process is to 

 be followed, that the leaves should be gathered between the 

 sixteenth and eighteenth day of their growth, and before 

 their borders become shaded with l)lue, as, when that takes 

 place, the indigo has arrived at a degree of oxidation which 

 prevents it from being completely dissolved. 



If the method of obtaining indigo by fermentation be 

 less advantageous than the one I have already described, 

 it is capable of being employed upon leaves which have 

 arrived at a higher degree of maturity, and I shall therefore 

 give a short description of it ; and I feel the more inclined 

 to do this, because in small manufactories this process is on 

 some accounts preferable to the other. 



When indigo is to be obtained by fermentation, a tub is 

 about three fourths filled with woad leaves, pressed down 

 so that they shall remain immersed in the water, which is 

 thrown over them of the temperature of 15° or 16° Reau- 

 mur, (=: 65° to 68° Fahr.) The heat of the manufactory 

 should be at the same degree. Fermentation will in a 

 short time be evident by the appearance of bubbles, which 

 rise and break upon the surface. This should be termi- 

 nated in eighteen hours. The period when it should be 

 stopped, may be known by the color of the water being 

 that of a yellow lime, and by the formation, upon the top, of 



