It seems that the aid of the engineer is necessary to overcome the difficulty of looseness of the grain caused by the severe pounding of the hides in the drums. The constant circulation of the tan liquor is required, but the hides should only be subjected to gentle motion. It is true there are tanning drums on the market which are said to obviate all the difficulty found in making sole leather in ordinary drums fitted with shelves or pegs, but a drum that meets the ideal conditions for the production of a solid yet flexible sole leather has not yet been invented. It seems that a kind of inner framework, to which the hides can be attached and which rotates much more slowly than the main drum, may solve the problem. The drum tannage permits the use of an excessive quantity of tannin, which, of course, adds to the weight of the leather. By the drum method of tanning, heavy hides can be tanned in two days after leaving the colouring pits; lighter hides are, naturally, tanned in less time, proportionate to their substance. The pit method occupies any time from one to fifteen months, although nowadays very few hides are left in the tan pits for a year. The methods of tanning just described relate chiefly to sole leather, but there is an enormous production of leather known as dressing hides, which are tanned, dried in the rough state, and sent to curriers or leather dressers for finishing. These hides are used for numerous purposes, including bags, portmanteaus, harness, saddlery, straps, belting, and boot uppers. The tannage of dressing hides differs slightly from that of sole leather; the liquors must be mellower and contain less insoluble matter, in order to obtain the necessary pliability, and a good, clear colour on the grain. A satisfactory tannage is obtained by treating the hides in oak bark liquors, which, in the later stages of the process, may be strengthened with oak wood, or myrobalan extract, or pure gambier, and completing the process in a tepid bath of sumach, which clears and lightens the colour. The drum is more suitable for the tannage of dressing hides than it is for sole leather. A quick method of drum tanning would be to treat the hides first in a 5 per cent. solution of neradol, the artificial tannin, and then complete the process with oakwood, chestnut, or quebracho extracts, or even in mixtures of these extracts. In this way, fairly good leather could be made in about two days. Neradol prevents the drawn grain and dark coloration that would result from the use of vegetable extracts alone.