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The passage intended for carrying off the dust should be placed underneath the stone, and beyond the point where the work is applied,

regarding the direction of the mo

tion. It should have a breadth a FIG.24

little greater than that of the stone, and a depth of eight inches, at most, for the largest stones. A sliding door serves to close it whenever dry dust is not produced. The water-discharge pipe should also have a valve, which may be closed when water is not used, and when it is desired to carry off the dust produced when the stone is trued.

The separate air-tubes from each stone lead to a collecting-pipe 16 inches by 12 inches, to which they are united by couplings.

If there are only four or five stones in the works, a single collecting. pipe will be sufficient, and the blower should be placed at the end. But if there are eight or ten stones in one line, it will be better to place a second collector, 16 inches by 12 inches, in the middle of the length of the first, and perpendicular to its direction. The blowing-apparatus should be placed in the extremity of the second pipe.

Finally, if there are two long parallel rows, witli eight or ten stones in each, they should also be connected with the second collector, or with a third, 16 inches by 20 inches, communicating with the ventilator.

In all these arrangements, movable valves should be placed at the junction of each of the pipes, to prevent the circulation of air in those which are not used at any time for carrying off the dust, since it is not intended to ventilate at the same time all the stones of the same mill. The valves placed at the head of each pipe should also be closed when it is not being ventilated.

But the greatest difficulty in rendering these places healthful, as in most other cases, arises from the carelessness of the workmen, and in the negligence of the foremen, who do not insist on the strict observance of the regulations.

76. Application. At Châtellerault's armory, the results obtained by Peugeot & Bros., of Valentigney, (Doubs,) in their bardware manufactory, were made use of, blowing-machines having been placed in two shops containing eachMain stones, 8 inches in diameter.... Grooving-stones, 4 feet in diameter......

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2 16

A fan-blower, 31 inches in diameter and 16 inches wide, parallel to the axis, and having a central opening 11 inches in diameter, making 900

to 1,000 revolutions a second, and requiring at most 8 to 10 horse-power to run it, easily removes all the dust produced during the truing of the two main stones and twelve of the grooving-stones, the other passages being closed.

The axis of the fan-blower is placed in the line of the last collecting. pipe, and is closed on the side opposite that pipe; the air carrying the dust is expelled at the outer circumference, which is entirely free.

Notwithstanding the success obtained in large works by the arrangements mentioned above, it would be better in all cases to separate the workmen into small shops of two stones each, each furnished with special ventilating-apparatus similar to that which we have described. Recent tria's seem to show that ventilation obtained by forcing in air would in this case prove very satisfactory.

DRYING-CHAMBERS.

77. The general arrangements which should be adopted for dryingchambers are in conformity with the rules previously given. The air should flow in at the top ; and, as in this case, it is always very hot, it enters of its own accord, but it is necessary that it should be introduced uniformly. The openings for the escape of the air saturated with moisture should be placed near the floor and on the whole circumference of the room. It is sufficient to connect the ventilating-pipes with the base of the chimney of the heating-apparatus.

The temperature wbich it is necessary to keep up in the drying. chambers depends upon the nature of the articles to be dried. For vegetable substances and flour, it need not exceed 1050 or 1100; for linen and cloth, 1580.

The particular conditions in each application may lead to some modi. fications of the general rules. Linen-drying rooms present a case which it is well to specify:

LINEN-DRYING CHAMBERS.

78. The arrangements for these useful accessories (Figs. 25, 26) to large bleaching-establishments have been carefully studied by Bouillon, Maller & Co. The linen is carried to the wringing-machine, which removes from it a great part of the water which it contains after having been washed; but it still retains about one-third of the total weight when it reaches the drying.room. When it is hung vertically, this water accumulates principally at the lower part, which therefore becomes hard to dry. Again, when the air enters through a single opening at the up. per part of the chamber, the interruption to the circulation of hot air caused by the linen wbich hangs in vertical bands and the force of the draught which tends to draw the air directly toward the ventilating-openings prevents the drying from proceeding uniformly, especially in large dry ing-houses. The observation of these irregular effects has led Bouil.

lon, Muller & Co. to adopt, for their latest linen-drying chambers, the following arrangements :

The chambers of which a drying-room is composed (Figs. 25, 26) are very small, and are at most 10 feet long, 4 feet wide, and 5 feet high, or 200 cubic feet in area.

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The floor is composed of two pieces of curved sheet-iron, forming at the same time the top of the warm-air chamber of the heater below. These two pieces of sheet-iron leave an opening o between them, which extends the whole length of the drying-room, and through which the hot air is introduced, which, after having dried the bottom and dampest part, rises with the vapor it produces toward the ceiling, and descends again to the ventilating-openings, arranged near the floor along the whole length of the side walls, the latter being made hollow and provided with pipes leading to the chimney, which also contains the smokepipe, as shown in the figures.

The linen is arranged outside of the drying-chamber on brass tubes sliding on iron rods extending the whole length of the chamber. These rods and the tubes which they carry are placed at the middle of a narrow door of the same height as the drying.chamber, which is only opened when the wet linen is put in, or the dry taken out.

Each chamber contains 8 rods. They receive, in two charges, 106

pounds of damp linen, in which 35 pounds of water remain after they bave been wrung.

The evaporation of these 35 pounds of water is effected in an hour by the consumption of about 11 pounds of coal.

The temperature of the chamber is kept at 1580, and the amount of air passing into the chamber varies from 35,000 to 42,000 cubic feet an hour.

Four chambers, with their 32 rods, are attended to by one woman, who fills and empties them.

According to the rules previously given, the 35 pounds of water evaporated, requiring 35 x 1170 = 40950 units of heat, and the 11 pounds of coal giving 159,000, the calorific effect of the apparatus is

40950 equal to 159000 = .26.

The same result was also obtained from some experiments made for seven years at La Saltpetrière, in which, with a consumption of 6,415 pounds of coal, 18,940 pounds of water were evaporated, the calorific effect in tbese experiments was found to be .24.

POWDER-DRYING ROOMS.

79. In the case of powdered materials spread out to a certain thickness, it is often necessary to use blowers which drive the air under a table, closed on all sides, the top of which is formed of wire-gauze, on which the substances to be dried are placed.

Thus, in powder.mills, the air driven under the gauze has ordinarily a pressure measured by a column of water or 4 inch high, and a tem. perature of 1120 to 1400. The thickness of the layer of powder varies from 1 to 3 inches, according to its nature. The air is heated to the proper temperature by means of water or steam pipes.

Although, in such cases, blowers are most frequently used, the same result may often be obtained by means of a well-regulated draught alone. At the powder-mill of St. Chamas, a drying-room, warmed by hot-water pipes placed under the table, and supplied with a chimney containing a hot-water vessel to produce a draught, has worked satisfactorily eren in the case of blasting-powder containing 8 or 9 per cent. of water.

BARRACKS.

80. The volume of air to be renewed every hour for each individual being given at 1,000 cubic feet during the day, and 1,400 to 1,800 during the night, the proportions and arrangements of the openings will be determined by the preceding rules.

But it is principally, and it may be said solely, during the night that the ventilation of the barrack-rooms is necessary, since, during the day, the soldiers are almost always out of it.

The heating of these rooms during the day is intended only to enable

those who return from duty, after getting wet, to dry their clothes and shoes; for this purpose, ventilating fire-places are preferable to sheet-iron stoves, because, in addition to the radiant heat they give out, they have in this case the advantage of carrying off the vapor arising from the damp clothing, which would make the room unhealthy and disagreeable. The fire never needs to be kept up long, and it cannot be counted upon to produce a constant change of air.

If natural ventilation alone be employed, it is necessary, according to observations made at the Bonaparte barracks in Paris, that the openings for the admission and discharge should be proportioned as follows:

Area of openings and flues to each bed in summer : discharge, 31 square inches ; adinission, 62 square inches.

In winter, spring, and autumn, these proportions would be excessive, and means should be provided for closing part of the openings, so as to confine the circulation of air within proper limits. But the regulation of the registers or valves should not be left to the discretion of the soldiers.

The necessity of preventing the soldiers, in their ignorance, from stopping up the escape-openings requires that in this case the rule should be violated which prescribes that these should be placed near the beds and the floor, as it will be necessary to place them near the ceiling, as well as those for the admission of fresh air.

The first should open above the space between the beds, and the flues should be placed near the smoke-flue or should receive the stove-pipe when stoves are used. The second, intended for the introduction of fresh air, are also placed near the ceiling, and made in the face of the opposite wall.

This arrangement presents the advantage that if, as often happens in ventilation due simply to the action of natural temperatures, the direction of motion changes so that the escape-pipe becomes that of admis. sion, no discomfort is experienced by the men, who in both cases are removed as far as possible from the openings.

These precautions will be completed by placing horizontal or inclined shelves under the openings, which will force the air always to remain nearly or quite horizontal in entering or passing out.

There is no reason to fear that the air flowing in will immediately rush to the escape-openings before circulating through the rooms; the difference of internal and external temperature will always enable the circu. lation to be maintained.

81. Utilization of the lost heat of cooking-stoves.-In most barracks, the cooking-arrangements of the companies which occupy that part of the building reached by one staircase, and often also all those used for a whole wing, are collected in a single room on the ground-floor, devoted to this purpose. There, separate stoves are used, in cooking, for each company, squadron, or battery. Beside these stoves, strongly heated twice a day, or even in their chimneys, it would be very easy and inex

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