Indigo Blue.—We give a solid dye of indigo blue to wool by plunging it into an alkaline solution of indigo white, and then exposing it to contact with the air. The solution of indigo white is prepared in a vessel usually from eight to nine feet in depth, and six to seven feet in diameter. This size is very convenient for the requisite manipulations, and presents a large volume of water, which, when once heated, is capable of preserving a high temperature for a long time. This vessel should be made of wood or copper. It always bears the name of vat. These vats are covered with a wooden lid, divided into two or three equal segments. Over this lid are spread some thick blankets. Without this precaution the bath would come in contact with the atmospheric air, a portion of the indigo would absorb oxygen and become precipitated. There would also be a great waste of heat. A most necessary operation, and one which has to be frequently repeated, consists in stirring up the deposit of vegetable and coloring matter which is formed in the vat, and intimately mixing it in the bath. For this purpose we employ a utensil called a _rake_, which is formed of a strong square piece of wood, set on a long handle. The workman takes hold of this with both hands, and, dipping the flat surface into the deposit at the bottom of the vessel, he quickly draws it up until it nearly reaches the surface, when, giving it a gentle shake, he discharges the matter again through the liquor of the bath. This manœuvre is repeated until the whole of the deposit seems to be removed from the bottom of the vessel. Before the tissue is dipped into the dye-bath, it should be soaked in a copper full of tepid water; it is then to be hung up and beaten with sticks. In this state it is plunged into the vat; it thus introduces less air into the bath, while it is more uniformly penetrated by the indigo solution. The cloth is now kept at a depth of from two to three feet below the surface of the liquid, by means of an open bag or piece of network fixed in the interior of an iron ring, which is suspended by cords, and fixed to the outside of the vat by means of two small iron hooks; the bag is thus drawn backwards and forwards without permitting it to come in contact with the air. When this operation has been continued for a sufficient length of time, the cloth is wrung and hung up to dry. Flock wool is also, for the purpose of dyeing, enclosed in a fine net, which prevents the least particle from escaping, and which is fixed in the bath in the same way as in the foregoing case.