All these arrangements, carefully planned in advance by M. Laval, and carried out as the building progressed, have cost but $5,000 for the complete purification of all the occupied parts of a school of three hundred scholars, which, estimating the interest on the cost and the wear and tear at 10 per cent., amounts to but $500 a year, or $1.67 a scholar. There can be no doubt that in such an establishment the health and the vigor of the youth, by reducing the number of sick days, would compensate largely, even in an economic consideration, for expenditures so well made.

It is, however, proper to remark that in winter the temperature may fall unusually low at Toulon, and that ventilation without heating may prove unpleasant. It would be easy to complete the beginning thus made by adding a few heaters.

WORKSHOPS.

68. During the day, it is usually sufficient to change the air two or three times an hour, according to the general rules given in § 38 and following.

If substances producing disagreeable or unhealthful odors are prepared or used, it will be advisable, if possible, to separate the sources of infection by partitioning off compartments almost as tight as dryingchambers, and carrying off the emanations by a strong local draught, carrying them under the floor and thence into a main ventilating-chimney, (Fig. 20.)

The fresh air brought in near the ceiling, and which should be hot or

to place near each workman a ventilating-opening, communicating with collecting-pipes terminating in a common ventilating-chimney.

The amount of air carried off in this way should be greater the more dangerous the materials are to breathe. It is then necessary that the air of the shop be changed at least three or four times an hour, and in some cases, such as in match-factories and other unhealthful works, it should be done eight or ten times.

In shops lighted by gas, and where every workman has a separate gas-burner, the products of combustion may often be readily removed

by placing above each burner a little iron or copper pipe, inch in diameter, leading to the outside of the building.

This simple and cheap method would suffice to render healthful a large number of workshops where unfortunate tailors, seamstresses, and others now live in an infected and unhealthful atmosphere.

Since the combustion of gas produces a great amount of vapor, the pipes which carry off the gaseous products should be short and direct to avoid condensation.

In addition to the disagreeable alteration of the condition of the air, there is often an excessive elevation of temperature in shops placed directly under the roof. We will mention further on the means for

remedying this by the inexpensive plan of sprinkling the roof.

69. Glue and soap manufactories.-In the preparation of these materials, and of many others of the same kind, there arise disagreeable odors during the boiling-operations. The most successful method adopted in England* appears to be to cover the vat and to make two openings in the cover, one of which admits the air, while the other, connected with the main ventilating-chimney, or with the grate of the vat itself, draws down the vapors and the air entering through the other hole, and carries them outside the building.

When there are many vats near each other, their ventilating-pipes are usually connected with a single pipe leading to the chimney.

If the odors to be carried off are merely unpleasant and not dangerous, and are not produced in great quantity, it will be sufficient to make a sufficient number of openings in the ceiling, provided with short sheet-iron pipes to produce the draft, and to make suitable provision for the admission of fresh air.

70. Manufactories of chloride of lime and similar substances giving off acid vapors.-The doors of the room into which the workmen have to enter are opened, and the rooms connected with a powerful ventilatingchimney. The workmen do not enter until all the vapors have been carried off by the fresh air introduced.

71. Match-factories.-The manufacture of matches, which produces the most distressing complaints, and to which boards of health do not pay sufficient attention, requires special details, into which it will be well to enter.

For this purpose, I quote from a very valuable report, made by M. Freycinet, mining-engineer, the following description of the plans adopted with success in a large establishment lately erected at Hemixeim near Antwerp, at which the builder, M. Genis, a talented Belgian officer, has made a remarkable application of ventilation by a downeast draught.

Five separate buildings, used for storage of raw materials, for covering with sulphur, for preparing the phosphorus-tips, for dipping, for drying and boxing, and for shipping constitute the manufactory proper. * Extract from the report of M. Freycinet Sur la salubrité des fabriques.

These are all ventilated by means of a large central chimney, 7 feet in inside diameter and 118 feet high, which receives the hot air from the furnaces of the steam-boilers, and, when needed, additional heat from a separate fire. Along the outer face of the side-walls of each building extends a subterranean passage-way of masonry, (c c, Figs. 21, 22,) 2

FIG. 21.

E

E

feet square, leading to the base of the chimney. Wherever the phosphorus is placed, an opening is made either in the walls or in the floor, communicating by a small pipe with the underground passage so as to carry off the injurious vapors without allowing them to spread in the shop.

Special arrangements differ according to the nature of the work. Thus, where the tips are prepared, a wide and shallow funnel is used, in

M

FIG. 22

"

E

which the draught is increased by the flames of the melting-fire.

The shop for the dipping and drying operations, which are the most dangerous, is particularly well ventilated. The general arrangement is shown in the two figures, (21, 22.) The building is 66 feet by 49 feet. Along the two sides are placed the drying-chambers E E E, 18 in number, each being 6 feet wide, 16 feet deep, and 7 feet high to the spring of the ceiling-arch, and 9 feet to the crown. They are connected with the ventilating-tunnel c c by a triple row of openings, 0, 0, 0, 10 inches by 5 inches, at the floor-level, and receive. the external air either by chimneys extending above the roof or by openings, 9 inches by 6 inches, placed at the bottom of the iron doors of the drying-rooms, and taking air from the main hall. The doors are 6 feet high and nearly 3 feet wide. The drying-rooms are heated by three rows of 2-inch steam-pipes placed under the floor. The channels in which these pipes are placed should receive cold air to be carried directly into the drying-chambers. Valves worked from the outside of the chambers control the admission and removal of air, which should enter with a temperature of about 1400, that of the chamber not exceeding 950.

In front of each range of drying-chambers there is a small railroad, extending from the melting-room to the warehouse. An iron car takes the prepared composition, and carries it to the drying-chambers in succession. Before each door or station, an orifice, o' o', made in the floor, exerts a powerful draught, which draws the vapors into the exterior lateral tunnel. The dipping is quickly done, and the frames are immediately placed in the drying-chambers, the iron doors of which are carefully closed.

The middle portion of the building is reserved for boxing. Under the tables are also placed ventilating-openings, o" o". The filled boxes are finally put in the car and carried to the warehouse.

The main passage-ways c c and c' c' enter separately into the base of the chimney, and are kept apart there by small vertical walls, in order to prevent contrary currents and to allow them to be regulated at will. By means of these arrangements, all smell of phosphorus in the main factory is prevented, and the men who work there are no longer exposed to necrosis. By taking the additional precaution of having them frequently visited by physicians, and of maintaining proper rotation in the hands employed in the different shops, they will be completely freed from this terrible disease.

MANUFACTORIES.

72. In some manufactories, it is essential for the quality of the products that the internal temperature be not allowed to fall below a certain limit; or, in other words, that the manufactory be heated even in spring and fall, and that the windows be kept closed. From this it follows that the air, not being changed, becomes gradually saturated with vapors and cutaneous emanations, and becomes at last unhealthful.

The workmen being thus kept continually perspiring, although they take off part of their clothing, go out afterward into the cold air, and often contract serious affections of the respiratory organs.

The conditions of the manufacture may be secured at the same time with those of hygiene by a strong ventilation, which shall constantly furnish fresh air of the necessary degree of temperature and even of moisture while regularly carrying off the foul air. With this change of air, a temperature of 750 or 77° will be found comfortable, and the workmen no longer be continually perspiring in an atmosphere constantly becoming more impure.

The rules to be observed are the same as those mentioned before, and a complete change three or four times an hour will usually be sufficient. The escape-steam from the engines is in such cases usually employed for heating, and it may be so regulated as to give the desired temperature to the fresh air, and the smoke-stack of the steam-engine will, without additional expense, maintain the draught required for carrying off the foul air.

In cases where the smoke-stack would be otherwise too small, the

draught may be increased or entirely produced in it by heating it by steam, or by placing a steam-jet in it as in a locomotive.

73. Workshops in which dust more or less dangerous to breathe is produced. In a large number of occupations, the division of the raw materials produces dust, which may be fine or coarse, heavy or light, harmless or injurious, and which it is important to remove from the workman and carry out of the building.

In most of these cases, ventilation, by means of a draught produced by heat, would be insufficient, at least unless it were made extremely powerful by an intense heat. It would be sufficient for light dust of very finely-divided materials, but for heavier dust, such as that produced by grindstones, it becomes necessary to use mechanical apparatus to force, through suitably-arranged pipes, currents of air at a proper velocity, which trial alone can determine.

In winter, when artificial heat may be required, as well as in summer, when it is unnecessary, it is essential that the discharge-openings should be placed as near as possible to the machines which produce the dust or emanations, and that the openings for admission of fresh air should, in general, be far off, in order that the velocity should gradually increase from the point of admission to that of exit.

But if the shop contain few workmen, if it is naturally sufficiently well aired, and if it is only required to carry off the dust as directly and quickly as possible, it would be better that the air be admitted under the cover which should completely surround the apparatus or the machine. above the point where the dust is produced, while the draught is applied below the same point and the dust is carried directly out of the building. The preceding remarks apply especially to those shops in which but a few detached instruments are used.

74. Cutlery-works.-One of the most dangerous occupations is that of the cutler. When proper precautions are not taken, the dust arising from the grindstones, which are used dry, enters into the respiratory passages.

These dangers are reduced and almost removed by the following ar rangements:

75. Grindstones used wet, (Figs. 23, 24.)-The stones should be sur