Besides the oxygenated compound, which is formed by the combination of oxygen with the extractive matters of the plants held in digestion, there is a production of carbonic acid which saturates the alkaline lee, and forms a carbonate of lime in the pastel vat. We find this attached to the sides of the vat in such quantity that the inside of these vessels becomes incrusted with it to a considerable depth. It is this product which dyers call the tartar of the vat; it effervesces with acids, and gives on analysis carbonic acid, lime, and a few particles of indigo. In the potash vat the solubility of the carbonate of potash prevents its deposition; but it is very probable that we have even here a formation of some carbonated products, perhaps in part formed at the expense of the carbonic acid of the air. The soluble extractive principle being the only matter which remains in solution in the bath with the indigo, the lime, &c., we have formed deposits which, varying both in their volume and in the greater or less facility with which they are precipitated during the various periods of fermentation, lead to a more or less considerable waste of time. If we plunge a piece of woollen tissue into a vat which has been recently stirred, it will acquire a dark color, and will be found covered with brown stains which are with difficulty removed. When the woad or paste vat has been stirred, it need be left two or three hours only before plunging in the stuff, at least during the early months of its working, inasmuch as the pastel, being but slightly divided and attenuated, is readily precipitated; but when, by reason of its extreme division, in consequence of repeated operations, it is thrown down with less facility, the dipping should not be performed oftener than three times in the day. The Indian vat requires less time than the others; we may even dye with it an hour after stirring the mixture. The potash, being soluble, forms no precipitate; while the ligneous fibre of the madder and the pellicles of the bran become deposited with great facility. We can also dip with these vats much oftener than with those made by pastel or woad. SICKNESS OF THE WARM VAT FOR DYEING WOOL, AND ITS REMEDIES. We have to thank that excellent practical magazine, “The American Chemist,” for the following notes on the sicknesses of the warm vat, by F. W. Kugler, translated from Reimann’s Färberzeintung:—