So far as I know, there seems to be no law of produce.  It is the most erratic and incomprehensible thing about planting.  One day your presses are full to straining, next day half of them lie empty.  No doubt the state of the weather, the quality of your plant, the temperature of the water, the length of time steeping, and other things have an influence; but I know of no planter who can entirely and satisfactorily account for the sudden and incomprehensible fluctuations and variations which undoubtedly take place in the produce or yield of the plant.  It is a matter of more interest to the planter than to the general public, but all I can say is, that if the circumstances attendant on any sudden change in the yielding powers of the plant were more accurately noted; if the chemical conditions of the water, the air, and the raw material itself, more especially in reference to the soil on which it grows, the time it takes in transit from the field to the vat, and other points, which will at once suggest themselves to a practical planter, were more carefully, methodically, and scientifically observed, some coherent theory resulting in plain practical results might be evolved.

Planters should attend more to this.  I believe the chemical history of indigo has yet to be written.  The whole manufacture, so far as chemistry is concerned, is yet crude and ill-digested.  I know that by careful experiment, and close scientific investigation and observation, the preparation of indigo could be much improved.  So far as the mechanical appliances for the manufacture go, the last ten years have witnessed amazing and rapid improvements.  What is now wanted, is, that what has been done for the mere mechanical appliances, should be done for the proper understanding of the chemical changes and conditions in the constitution of the plant, and in the various processes of its manufacture[1].

[1] Since the above chapter was written Mons. P.I.  Michea, a French
    chemist of some experience in Indigo matters, has patented
    an invention (the result of much study, experiment, and
    investigation), by the application of which an immense increase in
    the produce of the plant has been obtained during the last season,
    in several factories where it has been worked in Jessore, Purneah,
    Kishnaghur, and other places.  This increase, varying according to
    circumstances, has in some instances reached the amazing extent
    of 30 to 47 per cent., and so far from being attended with a
    deterioration of quality the dye produced is said to be finer than
    that obtained under the old crude process described in the above
    chapter.  This shows what a waste must have been going on, and what
    may yet be done, by properly organised scientific investigation. 
    I firmly believe that with an intelligent application of the
    principles of chemistry and agricultural science, not only to the