THE QUALITY OF THE AIR NECESSARY FOR THE HEALTH OF OCCUPANTS OF SCHOOL-ROOMS OR OTHER APARTMENTS.

2. This topic naturally succeeds that already named, since it furnishes the reason for the change in the air of apartments when occupied. In order to treat this subject intelligently, a brief statement of the composition of the air is here necessary.

Pure out-door air is composed of 79 parts of nitrogen, 20.96 of oxygen, and .04 of carbonic acid, and also a small amount of watery vapor.

Of the parties to this mixture the carbonic acid has special importance in connection with the subject of air supply, not because of actively poisonous qualities, as is the case with carbonic oxide, but because it is an exponent of the respiratory impurity of the air. Other dangerous products of respiration are doubtless evolved at the same time with the carbonic acid, and hence the amount of carbonic acid which is capable of measurement is taken as an expression of the entire product.*

* Billings on Ventilation and Heating.

There appears to have been a change of opinion as to the action of this gas upon the health of those who breathe it, and also as to certain other properties which it possesses. In consequence of its greater weight, it was for a long period taken for granted that carbonic acid would necessarily be found at the bottom of occupied rooms. Actual determinations, however, have shown that this gas, as well as others, is quite equally diffused throughout apartments.

There can be no doubt that the injurious effects of carbonic acid have been overestimated by confounding it with its excessively poisonous namesake, the carbonic oxide (or carbon monoxide), and I am also inclined to the belief that there has been too great a reversion of opinion in the direction of a belief in its harmlessness. The case of workmen in bottling establishments has been cited as an instance of its innocuous qualities, such men being constantly exposed to the liberation of free carbonic acid. In this case, however, there is quite a difference from that of persons exposed to the air of crowded apartments, since the carbonic acid is added to the normal air in the former case, while in the latter it is evolved at the expense of a portion of the oxygen of the room.

Dr. Angus Smith says upon this point that he had always considered carbonic acid as remarkably innocent, in small quantities, and was accustomed to look on the organic substances as the real evils; but his experiments in a tightly closed leaden chamber so far changed his mind that he was inclined to believe that carbonic acid had an injurious influence even in small amounts.*

The amount of carbonic acid added to the air of an apartment by an adult is about three fifths of a cubic foot per hour. At this rate one man would add to the air of a tightly closed apartment of 10,000 feet of air-space three cubic feet in five hours, raising the amount present to six or seven parts in 10,000, the exact ratio depending upon the amount previously present. In order, therefore, to reduce this amount to that consistent with health, a renewal of 3,000 cubic feet per hour, or 50 feet per minute, would

* "Air and Rain," by Robert Angus Smith, p. 179.

be required, and this amount would also be necessary for each added occupant.

Dr. Billings estimates twenty-five to thirty cubic feet per head and per minute as sufficient for school children.

A special reason for attention to the quality of the air supply, with reference to its pollution, is the enormous quantity which we use daily. We are wont to consider the quality of a water supply as a matter of the highest importance to the consumer, and justly so, and also to estimate the impurity of water by the number of grains per gallon, or parts per 100,000; and if we find a minute trace of ammonia or of other impurities, especially in connection with possible causes of pollution, we regard it as a dangerous water; and yet the average daily amount of water drank by each person is but a fraction of a gallon. On the other hand, when we consider the air supply, we find that each child at school takes into his lungs from 300 to 500 gallons of the air of the school-room in the five hours of his daily attendance, and each mechanic or operative in a work-shop breathes at least 1,000 gallons of the air of the shop in ten hours of labor. It is therefore a matter of the highest importance that the air should be pure and that the waste products of respiration should be removed as rapidly as possible and replaced by the pure out-door air. This is especially necessary in the case of work-shops and factories where processes are conducted in which dust or injurious gases are superadded to the products of respiration.

Combustion, both by fires and for heating, and also by gaslights, lamps, and other similar forms of lighting, has an effect upon the air similar to that of respiration, a single gas-burner producing six feet of carbonic acid per hour, which is eight or ten times as much as that produced by one adult. More thorough ventilation is therefore required for occupied apartments at night than by day, unless they are lighted by electric lights.

This diagram from Rietschel's Luftung und Heizung von Schulen illustrates the effect of respiration upon the air of an occupied, imperfectly ventilated school-room in Berlin.

The figures at the right side and the dotted line show the number of scholars present in each hour of the session.

Figures at the top represent the time of day in 10-minute periods.

Figures at left side and the black line show the amount of carbonic acid present from the opening to the close of school, including short recesses.

The dotted line near bottom represents the carbonic acid present in the out-door air.

Thus, at II A. M. there were present 54 scholars, and there were 7.2 parts per 1,000 of carbonic acid in the air of the room;

at ten minutes past 11, after a short recess, in which doors were open and the number of scholars reduced to 16, there were but 6.5 parts per 1,000 of carbonic acid, the out-door air remaining the same throughout the whole time.

The

Another quality of the air to which a certain amount of sanitary importance has hitherto been attributed is its moisture, and various devices have been contrived as attachments to heating apparatus for the constant supply of moisture to the air. actual importance of this quality of the air has undoubtedly been exaggerated. In many elevated regions persons live in a dry atmosphere without ill effects. Disagreeable sensations attributed to dryness of the air are believed to be due in a great measure to insufficient supply.*

The evaporation of water in hot-air furnaces is often a source of great nuisance, in consequence of the organic residue which is usually present in domestic water supplies, which soon becomes offensive in consequence of its concentration and charring by the process of evaporation.

The provision of an abundant supply of fresh, out-door air, and the regulation of the temperature at a point not too high, will usually furnish an amount of moisture which is sufficient for health as well as for comfort.

SOURCES OF AIR SUPPLY.

3. The proper source is always the out-door air; and the fresh-air inlets, whether to the air-ducts of furnaces or to the indirect coils of steam apparatus, or directly through the walls of apartments, should not be in the proximity of smoky chimneys, stables, and other generators of noxious odors, and especially should they be removed from the neighborhood of vaults, cesspools, and sewers. Too often have we found schoolhouses arranged with fine, sunny exposure to the southward, and at the same time the fresh-air inlets immediately adjoining some malodorous appendages upon the opposite side of the structure. Too often, also, is the air supply obtained from the cellar, and in some of the schoolhouses in our largest cities, otherwise well designed, special provision is made in the fresh-air inlets for openings into

* Dr. Billings on Ventilation and Heating, p. 62.