A is a pear-shaped pan, charged with the liquid to be evaporated; it is furnished with a dome cover, in which there is an opening with a flange f, for attaching a tube, to conduct the steam wherever it may be required. a is the fire-place; b, the ash-pit. The conical part terminates below in the tube g, furnished with a stop-cock at its nozzle h. Through the tube c d c′, furnished above and below with the stop-cocks c and c′, the liquid is run from the charging back or reservoir. During the operation, the upper cock c is kept partially open, to replace the fluid as it evaporates; but the under cock c′ is shut. The flame from the fire-place plays round the kettle in the space e, and the smoke escapes downwards through the flue i into the chimney. The lower cylindrical part g, remains thus comparatively cool, and collects the crystalline or other solid matter. After some time, the under stop-cock c′, upon the supply-pipe, is to be opened to admit some of the cold liquor into the cylindrical neck. That cock being again shut, the sediment settled, and the large stop-cock (a horizontal slide-valve would be preferable) h opened, the crystals are suffered to descend into the subjacent receiver; after which the stop-cock h is shut, and the operation is continued. A construction upon this principle is well adapted for heating dyeing coppers, in which the sediment should not be disturbed, or exposed to the action of the fire. The fire-place should be built as for the [brewing copper].
[Fig. 384.] represents an oblong evaporating pan, in which the flame, after beating along its bottom, turns up at its further end, plays back along its surface, and passes off into the chimney. A is a rectangular vessel, from 10 to 15 feet long, 4 to 6 feet broad, and 1 or 11⁄2 feet deep. The fire-bricks, upon which the pan rests, are so arranged as to distribute the flame equably along its bottom.
EUDIOMETER, is the name of any apparatus subservient to the chemical examination of the atmospheric air. It means a measure of purity, but it is employed merely to determine the proportion of oxygen which it may contain. The explosive eudiometer, in which about two measures of hydrogen are introduced into a graduated glass tube, containing five measures of atmospheric air, and an electric spark is passed across the mixture, is the best of all eudiometers; and of these the syphon form, proposed by me in a paper published by the Royal Society of Edinburgh in 1819, is probably the surest and most convenient. Volta’s explosive eudiometer as made in Paris, costs 3 guineas; mine may be had nicely graduated for 6 or 8 shillings.
EXPANSION (Eng. and Fr.; Ausdehnung, Germ.), is the increase of bulk experienced by all bodies when heated, unless a change of chemical texture takes place, as in the case of clays in the potter’s kiln. [Table I.] exhibits the linear expansion of several solids by an increase of temperature from 32° to 212° Fahr.; [Table II.] exhibits the expansion in bulk of certain liquids.
TABLE I.—Linear Dilatation of Solids by Heat.
Dimensions which a bar takes at 212°, whose length at 32° is 1·000000.