THE AGRICULTURAL JOURNAL. 



Indigo Manufacture, 



SUGGESTIONS BY PROFESSOR RUDOLF. 



{Concluded.) 



Preparations for the Market. 



THE slab of indigo is carried to the calce- 

 house on a stretcher by two men ; here it 

 is marked out into squares, and cut up with 

 a fine brass wire. On each cake a stamp 

 is impressed, showing the factory mark 

 and a consecutive number indicating the 

 day of manufacture, reckoning from the 

 commencement of Mahai. These cakes 

 are then placed on shelves made of bam- 

 boo slats, and are turned occasionally 

 during the drying process, which lasts 

 some weeks. 



In drying indigo no artificial heat is 

 employed, the ca:kes being merely left in 

 the cake-house goti ghur , the tempera- 

 ture of which is kept as equable as pos- 

 sible by opening and closing the numerous 

 shutters with which the house is provided. 

 In damp weather a heap of quick-lime is 

 soTietimes used to hasten the drying. 



When the cakes are dry, a specimen of 

 each kind manufactured is sent down to 

 one or other of the indigo market in Cal- 

 cutta, where they are assorted, and the 

 planter receives a list directing him 

 which of the cakes are to be packed 

 together. This assortment list is merely 

 a series of the numbers marked on each 

 day's cakes, commencing with the best 

 and finishing with the worst. The indigo 

 is packed in strong chests made of mango- 

 wood, which chests, after being marked 

 with the gross weight and tare, are com- 

 monly despatched to Calcutta for sale at 

 the indigo auctions, which are held in 

 November, December, and January. 



Of late years the practice of shipping 

 indigo to London for sale has been 

 adopted by some factories. 



The Calcutta indigo auctions are at- 

 tended annually by a large number of 

 indigo buyers, who come fully instructed 

 as to the special marks and qualities 

 which they are to purchase for their 

 employers. Until recently the market 

 value of the indigo was decided by the 

 appearance of a freshly exposed broken 

 surface of a cake, and more or less by the 



factory mark which it bore. From an 

 analytical determination of the amount 

 of indigotin contained in the sample, it is 

 not difficult to form a very correct opinion 

 as regards its suitability for dyeing pur- 

 poses and its market value. It is to be 

 remembered, however, that the market 

 value of an indigo does not at present 

 absolutely depend upon the percentage of 

 indigotin which it contains ; there are 

 other factors which rightly or wrongly go 

 to decide its worth. The amount of 

 indigo-brown contained in a sample is 

 said to exercise an influence in modifying 

 the shade which the indigo gives ; but 

 this appears doubtful, for in most dye 

 vats the reduction process used would 

 leave the indigo-brown as an insoluble 

 precipitate. Indigo of a good violet 

 colour is usually a high-priced commo- 

 dity, but whether the special shade of 

 the indigo cake has any connection with 

 the shade ultimately obtained on the 

 cloth seems rather an open question. 

 Again, the smoothness of the paste or 

 grain of iadigo is considered to influence 

 its value ; but it is possible that some- 

 times the roughness of a bad paste is 

 caused by impurities, although there ia 

 no reason to suppose that this is always 

 the case. It is quite possible to prepare 

 an indigo of good quality, rich in indigo- 

 tin, which acts satisfactorily in the dye- 

 house, but which would have a very low 

 value as determined by its external ap- 

 pearance ; the converse is also true. For 

 some years past it has been felt by many 

 interested that judging the value of an 

 indigo by its external appearance and 

 physical properties is not a satisfactory 

 basis for commercial purposes. Planters 

 consider that in some cases their indigo 

 has not fetched its real price, while the 

 buyers have a feeling that they are pur- 

 chasing more or less in the dark. But 

 while it is true that some indigos have 

 been sold below their true value, it must 

 be also remembered that other indigo 

 must have fetched a price above what it 

 would have done had its value been 

 determined on an analytical basis. 



