The flue for the reception of the soot must be made so long that hardly any smoke is perceptible at the end, which it is convenient to connect with a chimney with a good draught, regulated by a damper. In this case the combustion and the speed at which the products enter the flues are twice regulated. The material of which the flues are constructed through which the products of combustion are led influences the manner in which the soot is deposited; the portions nearest to the grate must be of stonework, but when the smoke has cooled to a certain extent different materials can be used in addition to wood; flues made of sacking stretched over laths are used. The fine flying soot adheres to the roughnesses of the coarse sacking, and is easily loosened by striking the wall of the flue. As we have said, the arrangements of most soot works are very primitive; they obtain only a fraction of the quantity of soot which they could produce by a proper regulation of the draught in the combustion chamber and in the flue in which the soot deposits. We shall now briefly describe the conditions which should be regarded in constructing a soot works; these conditions have not been found to be observed in any works we have seen, in this branch of chemical industry so-called practical experience is alone regarded, and consequently the ”practical” soot burner loses large sums, literally up the chimney. A black works can be properly designed by any one who knows sufficient chemistry to understand the process of combustion. Of this most educated men have some understanding, but the practical soot burner appears to have but hazy ideas on the subject, for one occasionally finds the arrangements for making soot in direct opposition to the proper disposition. For the sake of the uniformity of the product and of safety against fire, the flues in which the soot is deposited should be entirely of masonry; the joints of the bricks should be smoothly cemented over, so that soot cannot collect in quantity in them. The end of this flue should be connected with a high chimney provided at the top with a well-fitting damper, so that the draught in flues and chimney can be regulated at will or completely stopped. Such an arrangement, perhaps somewhat costly, has many important advantages: it is fire-proof, and when once warm remains so for a long time, since bricks are bad conductors of heat. When the flue is hot no water condenses in it; all the water formed in the combustion remains in the form of vapour, and is carried away by the chimney. A further advantage is that it is not often necessary to enter the flue to collect the soot; burning may be continued for a long time, and a large quantity of soot taken at once from the flues or soot chambers.