All the machines of this main type have their advantages and disadvantages, as they have their supporters and critics; but there can be little doubt that the balance of opinion among carpet yarn dyers is growing preponderatingly towards the second type of machine; that in which the liquor is moved through the yarn. In this type, the frame carrying the yarn is dropped into the vat, which is then covered with a lid. The liquor is then caused to circulate in a strong stream throughout the vat by propellers fixed at the head. The motion of the propellers can be reversed if desired. If both top and bottom sticks are used in the frame, they are placed at a less distance apart than the length of the skein, so that, the skein being completely immersed, the yarn is carried free of the stick by the flow of the liquor, access is given to all the wool fibres, and the danger of stick marks is avoided. The chief merit of this machine, however, is the considerable economy that is effected in steam consumption by the reduced size of the vat, as well as by the lid. The vat need only be made just large enough to contain the skeins dropped into it, whereas in the other type of machine it must be made large enough to allow for the skeins to be moved about in it. There is, therefore, less water to be heated for a given weight of yarn. The lid avoids loss of heat by radiation, which is inevitable with the open top types. The chemistry and the science of dyeing worsted and woollen yarns is a subject that can only be dealt with adequately at considerable length. Here a brief reference must suffice. Wool fibre is a substance similar in nature to horn, with a scaly surface. It is hygroscopic, being capable of taking up a large amount of water compared to its own bulk, and when moistened and heated it tends to soften and swell. These characteristics make wool very susceptible of being dyed. It is said to have an affinity for certain colouring matters, but this phrase serves to cover a want of agreement among chemists, as to whether dyeing is actually of a chemical or a mechanical nature. It is probably both. In any case, wool is easy to dye compared with silk, cotton, or other fibres. Natural dyestuffs, such as logwood, madder, fustic, cochineal, and indigo, are practically obsolete so far as dyeing for carpet yarns is concerned; and the modern dyer has a large range of aniline and alizarine colours to choose from. As is pretty generally known, the production of dyestuff from coal tar was originally a British invention, but its development passed into the hands of the Germans, upon whom, before the war, the dye consumers of the carpet trade, as of other trades, were very largely dependent. Necessity and enterprise have remedied this deplorable state of affairs, which need never recur. The coal tar dyes now being produced by British dye manufacturers are trustworthy and satisfactory, and they should improve both in quality and quantity as time goes on.