The cause of the “falling away” of the vat is a too active fermentation, which produces considerable lactic acid, from which butyric acid forms, setting free hydrogen, thereby making white indigo, which, if the action is allowed to continue, changes to a compound from which the indigo cannot be recovered. If lime is added, the lactic and butyric acids unite with it and precipitate it, while the excess precipitates the white indigo, which is slowly recovered, as fermentation progresses, which forms lactic acid, which, taking the place of the white indigo, sets it free. Besides the sicknesses, there are various results of mismanagement, of which the first is overwarming, which causes the bath to turn brown, which is the beginning of the souring. When the bath begins to sour from overheating, some logwood should be added and then bran, and the vat left to itself over night. The reason of it is that the temperature is too high for the desired fermentation to operate. The vat sometimes suddenly turns green, and even when indigo and the other necessary ingredients are added it remains of this color. This is called the “breaking up of the vat.” The reason is that the temperature is too low; to remedy it, it is necessary to add logwood and bran, warm it up, and stir, when it should stand for some End of the Project Gutenberg EBook of Notes Upon Indigo, by John Hayes