have had a good deal of mechanical training and above all must be a man of high-grade intelligence.

The modern thermostat, in which a metal bellows takes the place of a rubber tambour, has eliminated much difficulty. They are or may be made as sensitive to changes as the older type and are entirely free from the necessity of constant attention and such fluctuations as would come with the loss of elasticity in rubber.

VIII. VENTILATION.

It would require the writing of a volume to discuss exhaustively the problems connected with ventilation, and even then lack of exact knowledge would be much in evidence, for there are still many unsolved problems in this field. It seems wise, then, to limit the discussion in this bulletin to those demands which must be considered and met during the process of the construction of school buildings and leave the others to more technical treatises on school hygiene and engineering. Let us then set ourselves the task of answering as best we can this question: What are the requirements in the way of equipment and construction necessary to secure adequate ventilation of a modern school building?

Theoretically there is no satisfactory system of ventilation for many-roomed school buildings which does not use some form of mechanical means to force air into the rooms or to withdraw it from the rooms, or both to drive in and withdraw it at the same time. A gravity system of ventilation (that is to say, one where the air is caused to move by reason of different temperatures) can be made fairly satisfactory in medium to cold weather when the differences in the temperature required in the room and that prevailing outside are from 40° to 50° F. Plainly in mild or warm weather there will be very little movement in the air unless a wind is blowing, and for this reason it is difficult to make changes in the atmosphere in the classroom depending entirely on window ventilation. The reason that this is true lies in the physical principle that all air motion necessary in gravity or natural ventilation is caused by the difference in weight of the same bulk of heated or cold air. When we warm air it expands and becomes lighter, and hence will rise when surrounded by cold air, for the same reason that a cork will rise to the surface if immersed in a bucket of water. Water is heavier than cork and will thus displace it until it finds a balance at the surface where a part of it will rise above the water. Cold air is heavier than warm air and will displace it if opportunity is given for the warm air to rise; so if the air outside the room is cold and the air inside is heated, either by direct

or indirect radiation, there will be a pressure exerted from all sides and underneath the schoolroom by the heavy air to displace the warm air and drive it up, just as the cork is driven up from the pail of water. The cork does not come up of itself, neither does the warm air rise of its own accord. Neither would move were it not for the fact that each is displaced by heavier medium. This gives us the principle upon which all forms of natural or gravity systems of ventilation depend. If we remember that air when heated expands and bulk for bulk is lighter than cold air then we have a guide to the measurements of air currents in any gravity system of ventilation. Suppose, then, it is cold weather and we depend on heating the air about a furnace or steam coils in a basement and connect these heating boxes by means of a system of ducts with the various schoolrooms above. As the air is warmed it expands, becomes lighter, and is forced to rise by the greater weight of the same bulk of cold air which will rush into the duct leading from the outside to the heating surface, providing, of course, this entrance duct delivers the cold air underneath the heating surfaces and the ducts leading to the schoolrooms connect at or near the top of the heating chamber. Suppose the air outside is at a temperature of 20° F. and the fires warm the heating surfaces in the furnace so as to cause this cold air to take a temperature of 70° F. There will then be a strong upward movement of this heated air caused by the pressure of the cold air. This warm air will escape through the ducts arranged for the purpose into the schoolrooms. This warm air is pure air, if it comes from a good source and the heating surfaces are properly made, and hence the schoolrooms are being supplied with pure, warm air. But it is plain from what has been said that the amount of such fresh air delivered into the schoolrooms will depend on the size of the ducts and the rate of the movement of this fresh, warm air. Try another experiment with the cork by embedding in it some leaden pellets, such as shot, to see if the rate of its movement from the bottom of the bucket to the surface of the water will be increased or decreased. You know what the result will be before trying. The less the difference in weight between the cork so loaded and the same bulk of water the slower will be its upward movement. Exactly the same thing happens by reducing the difference in weight (that is, the amount of expansion) between the air ready to enter the schoolroom and that outside. Suppose, for example, the air outside is at a temperature of 50° F. To heat it to a temperature of 68° F. will cause less difference in expansion and therefor less difference in weight. Hence the rate of movement will be slower and less warm, fresh air will enter a room within a given time.

Thus the ventilation of that room will be less rapid and will supply the needs of fewer people.

Children of the primary grades, gathered in a schoolroom, need 2,000 cubic feet of fresh air per pupil each hour. Students of highschool age need 2,500 cubic feet. This does not mean that they will individually breathe so much, but that each will vitiate that amount. They will each breathe approximately 18 cubic feet per hour, but when a breath of air is exhaled it has lost so much of its oxygen and has taken up from the blood so much carbonic-acid gas that one exhaled breath will vitiate more than a hundred times as much fresh air to such a degree that none of it will be fit to breathe. This vitiation consists in reducing the normal amount of oxygen, but especially in increasing the normal amount of carbon dioxid and throwing into the air bad odors and possibly some sort of toxic agent produced through fatigue.

Since the first edition of this bulletin was prepared much investigation has been undertaken with reference to proper methods of ventilation. The most notable work done in this field is that of the New York Commission on Ventilation. After two or three years of experimental work, in which ample means and trained specialists were at command, the following conclusions represent in part the results of their labor:

1. The amount of carbon dioxide in ordinary classrooms, even under condition of poor ventilation, is of very little danger.

2. The depletion of oxygen in a badly ventilated classroom is insufficient to cause appreciable harm.

3. The chief difficulty lies in the interference with the normal escape of heat from the bodies of the children, due to the lack of the dissipation of the blanket of heated and moist air with which they are surrounded.

4. In order that these disadvantages may be obviated, it is necessary to keep the air in the classroom in motion, and to keep it from becoming too warm.

5. The outstanding result in the condition of those who are subjected to badly ventilated workrooms is loss of appetite.

This much-talked-of and fairly thoroughgoing investigation seems to make it clear that the chief problem is to keep the air in motion within the classroom, so that the bodies of the children will be kept at the proper temperature and the blanket of moisture gathering about the bodies be carried away. This looks as if it would be necessary, if the recommendations of the commission be carried out, to install within the room some mechanical device to keep the air in motion rather than to depend upon a central plan of fans to drive the air into the room. The fact is we are still in doubt as to the best methods

of supplying, at a reasonable cost and without other disturbances, the best sort of mechanical schemes of ventilation. It is very plain that it is perfectly possible to install sufficient fan power in the basements of buildings and connect these up with properly placed ducts with the classrooms to furnish ample and thorough ventilation without the necessity of installing fans within the rooms. But the trouble comes in the expense of installation and in the running of such fans. There are thousands of fans installed in school buildings totally inadequate to do the work they are supposed to do. There are hundreds of others sufficiently powerful but are not operated because of the expense connected with their operation. The truth is (and boards of education should understand this thoroughly) it is a very expensive process to install fans of sufficient power to ventilate all schoolrooms properly and a much greater and a more constant expense in the long run to keep them running. It is disheartening, to say the least, to see how many school buildings are supplied with fans that never run. Literally there are millions of dollars' worth of ventilating devices rusting out in the large school buildings of this country. It stands to reason that one of two things ought to be done. Either fans must not be installed, or, if adequately installed, they must be kept running. Boards of education must be frankly told that mechanical systems of ventilation are very expensive, and unless they are willing to bear this expense constantly and regularly it is a serious blunder to introduce fans. The safest plan, at least temporarily, is to heat by direct radiation and ventilate through the windows. I am fully aware that this throws the responsibility wholly upon the teacher so far as maintaining ventilation is concerned, and that it also introduces the difficulty of ventilation in mild weather, when the air currents move very sluggishly. Possibly the next step will be the introduction into rooms of individual electric fans to help keep the air in motion, still depending upon the windows for intake and exit. The whole problem of ventilation is still far from being solved, and boards of education should be warned against any so-called mechanical system without the best of disinterested advice and the knowledge that they must pay heavily for the results obtained.

While it seems established that temperature and humidity are the chief factors to be considered in ventilation this does not mean that increase in carbon dioxide and decrease of oxygen content may be totally disregarded, and it is not at all proven that odorous substances given off from the body are not depressing and that toxic materials may not also be present in respired air.

The best thing to do is to keep the air in classrooms as near to that of the outside air as possible, when that outside air is at the proper temperature, in order to prevent undue accumulation of heat

in the body. The big problem, of course, is to induct sufficient fresh air into the schoolrooms, distributing this equally and keeping it moving at such a rate as to dissipate the blanket of moisture gathering about the bodies of the children. The best possible way of doing this has not been demonstrated, but at present (knowing the tendency everywhere to neglect the use of fans in ventilating classrooms) the best results may be obtained by the use of properly adjusted windows, properly oriented, and handled by teachers who thoroughly appreciate what they are trying to do. (See Appendix on Orientation of Buildings in Southern States.)

IX. TOILETS.

The walls of toilet rooms should be made of white tile, glazed brick, or hard cement and finished with a hard waterproof white paint. All schoolmen know the difficulties encountered in keeping the walls of these rooms free from obscene writings and drawings. They also know that the neater and better the toilet rooms are prepared at the first, the less apt the walls are to be defaced. The walls of dark and dingy toilet rooms are the very ones, other things being equal, that suffer from such indiscretions. Young people respect and care for these rooms when decently made, flooded with light, and acceptably ventilated. And when we are arguing for this care in planning and construction we are doing so not only from the point of view of sanitation and convenience but also for the sake of moral values. Where glazed tiles or bricks can not be used, due to the expense, specially prepared hard cement plaster and hard waterproof paint may be used with a fair degree of satisfaction. In order to keep these rooms free from evil suggestion, then, flood them with light and keep the walls scrupulously clean.

Toilet rooms should be so constructed as to offer direct drainage through a trap with sewer connections. In the girls' room this should be on opposite sides from the seats or toward the front, so that the drainage may flow from the seats toward the outer wall. In toilet rooms designed for boys no special opening is necessary, for the drainage can be made through the urinals. While to some the foregoing directions may seem unnecessary, it has been found by extended observation that a great many blunders have been made in these details.

Elsewhere it has been suggested that the toilet seats should be set in a single row and not back to back as most frequently found. It is almost impossible to light stalls when set back to back, and then it is difficult to inspect such rooms quickly and see that all conditions are justifiable. Naturally this requires a little more space