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origin is given off in the wood-working manufactories. The hard woods used in cabinet-making are especially injurious. In factories where hides and feathers are used dust of animal origin is found. In the arrangement of modern manufacturing establishments much of the danger from dust particles is overcome by special arrangements, by means of which the dust is extracted from each machine and is removed by a special flue by means of a strong current of air.

Examination of the Air by the Senses.-Immediately on entering the place where the air is to be examined, note the condition of the air as presented to the olfactory sense. Note whether it is fresh and sweet, rather close, very close, or fetid. The odor of animal organic matter when present in the air, even in small amounts, is very offensive and readily detectable, if the first impression on entering be noted; after half a minute this impression wears off. The readiness with which it is perceived depends largely on the humidity of the air, more so than on the increase of the temperature. A rise of 1 per cent. in the humidity has as much influence on the condition of the air, as judged by the sense of smell, as a rise of 2.32° C. in the temperature.

The recognition of the presence of organic matter in the air is the most important item of information to be gained by the senses; but the presence of illuminatinggas or any abnormal smell should, of course, also be noted, as well as the humidity of the air and the presence of notable quantities of dust.

Chemical Analysis of Air.—This includes, first and most important, the determination of the proportion of carbon dioxid, since this is commonly taken as an index of the other impurities in the air; second, the estimation of the humidity of the air; and, third, the determination of the quantity of oxidizable organic matter, as shown by the potassium permanganate test. A more complete chemical analysis would include the estimation of the amount of oxygen present, the amount of ammonia (free

and albuminoid), the amount of nitrous and nitric acids, of hydrogen sulphid, etc., in the air.

The proportion of carbon dioxid in the outside air should always be determined at the time when the air of an enclosed space is being examined. The excess of carbon dioxid in the inside air over that in the outside air is termed the "respiratory impurity" of the air. When, however, it is impossible to analyze the outside air, 0.4 may be taken as the average content of carbon dioxid per 1000 volumes of air.

Estimation of Carbon Dioxid in Air.-It has long been the custom to gauge the relative purity of the atmosphere of confined spaces by the determination of the proportion of carbon dioxid present. It has been shown that all the impurities of the air arising from human occupation increase in a fairly constant ratio, and that the estimation of the proportion of carbon dioxid in such air is indicative of the corresponding increase of the other impurities, such as organic matter, ammonia, moisture, etc. Moreover, on account of the relatively greater simplicity and accuracy of the methods of estimating the carbon dioxid the determination of the carbon dioxid content of air is generally employed in estimating the purity of an atmosphere.

The methods employed in the laboratory for the estimation of the carbon dioxid content of air have been devised by von Pettenkofer. Of the two methods devised by von Pettenkofer, that known as the flask method is the more serviceable. In both methods a solution of calcium, barium, or strontium hydroxid, of definite strength, is exposed to a known volume of air in a tared flask so as to combine the carbon dioxid with the basic hydroxid to form the corresponding carbonate. The subsequent titration of a portion of the alkaline solution with an acid solution of known strength shows the amount of the alkaline hydroxid that has been neutralized by combining with the carbon dioxid of the air.

In the flask method the air is forced into a four-liter bottle, the capacity of which has been accurately deter

mined, by means of a hand bellows. When the bottle has been filled with the air to be examined, it is closed with a rubber cap. The alkaline hydroxid solution is now introduced by carefully lifting the rubber cap and again replacing it. In the von Pettenkofer tube method the alkaline hydroxid solution is placed in a specially constructed tube through which the air to be examined is slowly aspirated.

Estimation of the Humidity of Air.-The relative humidity of the air of a room is most readily determined by means of a sling psychrometer. Fairly satisfactory results can be obtained by means of a properly managed stationary psychrometer (Fig. 3), or with the hair hygrometer (Fig. 4, p. 39).

Estimation of the Organic Matter in Air.-The proportion of organic matter can only be determined indirectly, either by estimating the amount of oxygen required for its oxidation, or by determining the amount of nitrogenous

b

FIG. 5.-Apparatus required with this method. It consists of: a, a small glass tube, twenty centimeters in length, consisting of a narrow portion four centimeters long and three millimeters in its internal diameter, and a dilated portion sixteen centimeters long and twelve millimeters in its internal diameter. This tube contains the granular pumice-stone which serves as the absorbent material in this method; b, is the gas-meter; and c, a Chapman water pump.

organic matter from the quantity of free and albuminoid ammonia obtained through distillation.

Thus far the methods devised for the estimation of organic matter in air have not proved very satisfactory. One of the principal reasons for this fact is the necessity of very careful manipulation to avoid unusually large ex

perimental errors. The method which has given most satisfactory results in my hands1 is that devised by Remsen (see Fig. 5), in which the air is aspirated through a small glass tube containing freshly ignited pumice-stone which has been moistened with twice-distilled water. After a definite volume of the air has been drawn through such a tube, the amount of organic matter adhering to the pumice-stone is determined either by the Wanklyn method as free and albuminoid ammonia, or by boiling with permanganate of potash solution as in the estimation of oxidizable organic matter in water.

Diseases Produced by Impure Air.-Carbon Dioxid. -This gas is poisonous in proportions exceeding 1 or 2 per cent.; but there is no doubt that the constant presence of even smaller amounts for long periods of time induce a progressive depression of the vitality, thus constituting a preparation for, and a predisposing cause of disease. The bad effects produced by breathing air vitiated by respiration are in part, though not entirely, due to the contained carbon dioxid.

Carbon Monoxid.-This is a powerful narcotic poison. Its poisonous action depends on the formation of a new and quite stable compound with the hemoglobin of the blood, the oxygen being entirely displaced. It produces unconsciousness, paralysis of the heart, and, at high temperatures, convulsions. Small quantities cause headache, giddiness, and speedy insensibility. A mixture of carbon monoxid and dioxid seems to be more poisonous than the monoxid alone.

Hydrogen Sulphid. This gas acts as a narcotic poison; I volume per 1000 volumes of air being fatal to dogs. The chronic effects produced by the inhalation of small quantities are depression, digestive disturbances, and anemia, with narcotic or convulsive symptoms in more acute and

severe cases.

Effects of Vitiated Air Generally.-Vitiation by Respiration and Perspiration.-It is impossible to sepa1 Smithsonian Miscellaneous Collections, No. 1037, 1896.

rate the effects produced by these two forms of vitiation from one another, nor is it necessary, as they always coexist. In addition, the emanations from the alimentary tract are also a possible source of impurity. The effects produced by vitiated air of this character may be divided into two classes, those of extreme vitiation acting for a short time, and slighter vitiation extending over a long period of time.

Extreme vitiation for a short time, as produced by great overcrowding, may cause death from deficiency of oxygen and excess of carbon dioxid in the air breathed. It was supposed until recently that a large share of the effects produced by such an atmosphere was traceable to the organic matter present in expired air, but at present there is no convincing evidence that such is the case. On the other hand, the experiments on animals indicate that deficiency of oxygen, excess of carbon dioxid, increased temperature, with high relative humidity of the air, are the principal factors in producing the effects. The increased temperature, high relative humidity, and lack of movement of the air are the most important factors in producing the effects through their operation upon the heat-regulating functions of the body.

Experiments on human beings confined in a small airtight chamber have demonstrated that when the degree of vitiation has become sufficiently great to induce marked discomfort in the occupants, the discomfort disappears very quickly when a fan is set in motion and the air brought into active circulation. That the discomfort is due to interference with evaporation from the skin is shown by the fact that a person confined in such a room, but breathing fresh outside air, experiences an equal degree of discomfort to those. in the room, and by the fact that a person outside the room, with his body exposed to fresh air but breathing the air of the room, experiences no discomfort.

These experiments show that vitiated air may be breathed for a considerable time without experiencing

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