In these several ways we have endeavoured to meet the requirements of a theoretically perfect bath. We have contrived an instrument that provides a vigorous current of heated air of definite temperature under perfect control of a self-acting source of beat, and out of reach of contamination by the results of combustion. Taken together, these result are, I submit, satisfactory, and show the instrument to be a substantial improvement on the ordinary air-bath.
As regards regulation of temperature, this is as simple as possible. It can be 'set at any temperature wished for, from that of the room up to any degree that can be required, in the course of a few minutes. I have only to undo the screw (F) and allow a little of the air contained in the copper chamber to escape, and when the desired temperature is reached, screw it down again; this, by preventing further escape, fixes the temperature at that point. On the other hand, if I want to lower the temperature, I should turn the gas out and allow air to enter the copper chamber until the temperature stands at the desired point, A thermometer hangs from the chimney, and the temperature can be seen at any moment. The regulation can be accomplished not only exactly but immediately, and moreover, the temperature is absolutely fixed. It may be set going on January 1st and go on to December 31st, and it will not vary. It may do some good to put some asbestos on the upper surface of the diaphragm that divides the drying and combustion chambers. (M. A. Adams, F.R.C.S.)
(c) Chloride of calcium is cheap (beiug a waste product), easily portable, and when it has absorbed moisture it can be again made fit for use with no more complicated apparatus than an iron pot. Air dried by means of chloride of calcium has, therefore, very naturally come into use for drying purposes. But it is sometimes employed in an unsatisfactory manner, by a mechanical arrangement. The chloride of calcium is alternately exposed to the current of air to be dried, and is then passed into a furnace, in the expectation that moisture will thus be alternately absorbed and expelled. This view seems to be erroneous. Chloride of calcium parts with two-thirds of its water at 392° F., and loses the remaining third at a higher point. Unless the heat is carried to this point, the chloride of calcium does not recover its original capacity of water. If it has been thus heated, it wants sufficient time to enable it to cool down to n temperature below that at which it parts with its moisture. Chloride of calcium, at temperatures above the boiling point of water is a comparatively poor desiccating agent. There is another method in which chloride of calcium may be applied in desiccation, a method often used in the laboratory.
The substance to be dried is placed in a vacuum - or even in a closed receiver, filled with air at the ordinary pressure - along with trays of chloride of calcium. In this manner, the moisture evaporating from the material is at once absorbed, and fresh moisture can be given off to take its place.
(d) In Fig. 19 is shown an excellent apparatus for drying grain, tea, and every kind of agricultural product. The reference Utters indicate as follows i -
A, Brick bra in which coke is burnt, or a, flue to conrey waste heat from any furnace. B, Compound wroughtiron fan, which will draw waste heat from a distance of 50-100 ft. C, Chimney and valve, to cany off smoke when fira U first lighted. c, Thermometer or Pyrometer. D, Feed-hopper, into which the grain is conveyed by an elevator from below, or by a shute from an upper floor. E, Cylinder; when of 18 ft, and upwards, can be made in two lengths, joined in the centre by flanged rings. F, Elevating gear for raising and depressing cylinder. G, Air-duct made of different sections to suit different products. H, Part of the outer shell removed to show the cells in which the grain is carried up and poured out in a continual stream; - the number and pitch of these cells is also varied for
(e) The cool air drying machine which weire about to describe, is based upon the principle of drying the air before it in turn is used to dry the material to be operated on; and this drying of the air itself is performed by bringing it into contact with a system of iron tubes heated in a furnace to about 1300° F., when part dissociated into raygen and hydrogen. Theoiygen attacks the surface of the of iron, snch as nails and filings, placed there for the purpose, and the hydrogen passes away with the rest of the air. If, now, this mixure of dry air, with a small percentage of hydrogen, be cooled again to the original temperature, it will be capable of taking of as much moiature as it originally contained. Power is supplied by a Robey undertype steam engine, which works two fans placed under a wooden box, and a number of vertical agitators placed in the drying chamber between the stacks. The air from the fans is forced through a series of vertical tubes placed in a box technically termed the " cooler." After passing the tubes, it is forced through another series of tubes placed in the "furnace," and is there heated to about 1300° F. After passing through the furnace tubes, the air is conducted back to the cooler; but this time it surrounds the outside of the vertical tubes, and flows finally to horizontal flues placed on the ground, which lead into the drying chamber.
The air, on coming from the furnace, is cooled by contact with the outside of the tubes, through which fresh air is pushed into the furnace; and the cooler in this manner performs two functions, viz. it heats the air on its. way to the furnace, and it cools the air after it has left the furnace. The machine is provided with a second cooler, technically termed the "water cooler; " but this is an addition made merely for the purpose of experimenting. The water cooler is arranged somewhat in the manner of an ordinary surface condenser of a steam engine, with the only difference that, instead of exhaust steam, the air coming from the air cooler is passed through it. This water cooler can be filled more or less with water, and the water can be renewed at a faster or slower rate. By this means, its cooling effect upon the stream of air can be varied so as to obtain the dry air finally at any desired temperature between 150° F. (the temperature to which the air cooler reduces it) and 60 F., or even less if desired. The water cooler is never used in drying machines when not required for experimental purposes; for actual practical work an air cooler alone is used, and its size is so chosen as to reduce the temperature of the air to the desired degree.
The goods to be dried are stacked on trolleys and run into the compartment, care being taken to put the heaviest stuff first, because it requires a longer time to get dry. The agitators are worked from bevel gear overhead, and are placed over the main flues by which the dry air is conveyed to the drying chamber. A hole about 10 in. diam. is cut in the top of the flue below each of the agitators, and the air streaming up through this hole is scattered about by the fans of the agitators, so as to penetrate the interstices left between the stacked goods. In this way the whole of the surface is evenly surrounded by a gentle stream of dry and comparatively cool air. The air, as it passes through the stack, becomes charged with moisture, and if it were not quickly removed, it would impede the further process of drying. To facilitate its removal, exhaust fans are arranged to draw the air through the hollow lining of the walls of the drying chamber, and discharge it into the atmosphere. The whole air contents of the drying chamber, when full, are changed every two minutes.
At the time of our visit, we saw in the drying chamber mahpgany boards 2 1/4 in.-3 3/4 in. thick, oak flooring, also some walnut gun stocks, a large pile of billiard cues, and a big parcel of pine deals 12 ft. by 9 in. by 3 in. The best proof that the drying of the wood is effected without warping lies in the fact that billiard cues can be successfully treated. Boards 1 in. thick require to be left in the drying chamber for about a fortnight, 2-in. stuff would be left in a month, and so on in proportion to the thickness for heavier stuff. We may take it that to stack mahogany boards in the open air in order to season the wood in the old way,would cost about 6s. a square, that is, inclusive of ground rent, fire insurance, and interest on the capital lying idle. The timber will in that case take about twelve months to become seasoned. If artificially dried, the process will be completed in a fortnight at a somewhat smaller charge than 6*. per square. Thus the artificial method is not only cheaper, but it has the great advantage of enabling the money to be turned over quickly, instead of lying idle in stacks. (Industries.) Water ovens. - In Fig. 20 is shown a constant water bath, consisting of a square box A, supported over a Fletcher's solid flame burner.
The top of the box, 15 X 15-5 in., is formed by a brass plate, i in. thick, which thus is stiff enough to support a considerable weight without yielding, the sides and bottom being sheet copper. From the point, B, projects a 1/2-in. brass tube, B C, which tarns up at a right angle. At E is a stop-cock, which is connected by a thick rubber tube with the glass tube, D F, which is fastened against the adjoining wall. Connected with C by a rubber joint is a 1/2-in- block tin tube of 20 ft. length, which extends up the wall iu the manner shown to the highest point, T, and thence returns and ends just over the slightly funnel-shaped top of the glass tube at D. The hath being filled with water to just the level, 11 6, may be kept constant by boiling for many the steam being condensed in its passage up, or, if uncondensed before it reaches the point, T, in its passage down Ihe block tin tube. Id flat-bottomed platinum or porcelain capsules, evaporation goes on very rapidly when placed on top of this water-bath. The whole surface of the bath is nickel plated. (Journal of Analytical Chemiastry.)
Apparatus for dryinng grain, tea. etc.