MORDANTS.

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inside and 40 feet high, with a mid-wall from bottom to top running length-wise, so as to form two apartments, each 11 feet wide : in one of these apart-ments the goods first receive the moisture they require. Besides the groundfloor it has two open sparred floors, 26 feet apart, upon each of which is fixeda row of tin rollers, all long enough to contain two pieces of cloth in theirbreadth. The rollers, being threaded, are set in motion by a small steam-engine; and the goods to be aged, which are at first placed in the groundfloor, are drawn into the chamber above, where they are made to pass overand under each roller, issuing at last at the opposite end, where they are foldedinto bundles on one of the three stages which are placed there. These stagesare partially separated from the rest of the chamber by woollen cloths.While the goods are traversing these rollers they are exposed to heat andmoisture, furnished to them by steam, which is made to issue gently fromthree rows of trumpet-mouth-shaped openings. The temperature is raised X,from 8o° to ioo° F., or more, a wet bulb thermometer indicating at the sametime 76° to 96° F., or always 4 0 less than the dry bulb thermometer. In thisarrangement 50 pieces of 25 yards each are exposed at one time, and, as eachpiece is a quarter of an hour under the influence of steam, 200 pieces passthrough in an hour. Although workpeople need scarcely ever enter thewarmest part of this chamber, a ventilator in the roof is opened when thereis any considerable evolution of acetic acid. The mordant does not, however,become fully “ aged ” by this process alone, although it is aded upon as muchas if it had hung a whole day in cold air. It has received, however, therequisite quantity of moisture, about 7 per cent of the weight of the piece,and is thus enabled, if the mordant be iron, to take oxygen from the air, andto become changed with time into the sesquiacetate and sesquihydrate ofoxide of iron. In order to be sufficiently aged it must be left one or two, oreven three, days in an atmosphere still warm and moist.

It had been ascertained long before, at Thornliebank, that exposure in singlefolds after moistening was not necessary. The experiments of the late Prof.

T. Graham, on the diffusion of gases through small apertures, had served tosuggest that, for the absorption of the small quantity of oxygen required, thegoods might as well be wrapped up and laid in heaps. Accordingly, in theoperation in question, the moistened goods are carried in bundles into thebuilding, on the opposite side of the mid-wall already mentioned, and laidupon the sparred floors, placed at heights corresponding with the stages in thefirst apartment. Upon these floors 7000 or 8000 pieces may be laid at a time,and, since each piece is 25 yards long, 100 miles can be stored at once. It isnecessary, of course, that an elevated temperature and a corresponding degreeof moisture be preserved in the storing apartments, day and night, and 8o° F.is sufficient, with the wet bulb thermometer at 76°. To effedt this condition alarge iron pipe is placed along the ground floor underneath, and moderatelyheated by steam, while a row of small jets in the same position are made toprojedt steam diredlly into the air of the room. The whole building is protedted Xfrom external cold, and consequently from condensation of steam, by a warmedentrance room, and by double windows, thick walls, and a double roof. Small *steam-pipes are also placed at other points where they seem to be required,and the apartment which contains the rollers is specially heated, when not inuse, by a couple of steam-pipes, which are placed under the ceiling of theground floor.