the atmosphere by sheep, pigs, horses, and cattle generally, and that is the large quantity of marsh gas which escapes from the intestine. A certain quantity is occasionally produced in the human body, and also contaminates the air, but it is entirely insignificant to the regular and normal production of the intestinal gases of the herbivora. Regnault and Reiset have made some excellent determinations of the amount of oxygen consumed, the carbon dioxide and marsh gas exhaled of sheep, pigs, and calves. The following is an abstract of the results of their investigations:-- Presuming that the ratios found by experiment for calves hold good for cows and horses, an average-sized cow of 230 kilos weight would consume 1104 grms. of oxygen per hour, and would exhale 1288 grms. of CO2, and 307 litres of marsh gas. It would therefore render every hour 3714 litres (13.2 cubic feet) of air irrespirable. Horses would give similar numbers. Sheep of average size spoil 112.6 litres (3·97 cubic feet) per hour of air; calves 154 2 litres (5.20 cubic feet); pigs of moderate size 165.8 litres (5.85 cubic feet); rabbits about 10 litres (37 cubic feet); fowls, 10 litre (037 cubic feet); medium-sized dogs, 23.5 litres (79 cubic feet); a cat, 10 lbs. in weight, 178 litres (6 cubic feet). If we could only regard respiratory impurity, it would be correct to say that 10 sheep contaminated the air in about the same degree as 8 men; that calves and pigs were more than equal to a man; that 14 rabbits or 140 fowls were equal to a man; but in practice such animals contaminate the air very much more than the above, for they are ever associated with their own excreta, and their intestinal gases passing into the air are additional impurities. (35) Quantity of Air required per Head per Hour Ventilation is the art of supplying without perceptible draught1 the requisite quantity of pure air. It has been already stated that every hour an adult man renders absolutely irrespirable 5 cubic feet of air; a man under certain circumstances such as in an air-tight chamber containing the necessary appliances to remove promptly the carbon dioxide by a continuous spray of strong potash, to absorb the excess of aqueous vapour by means of anhydrous chloride of calcium, and in some way or other to deal with organic matter evolved from the lung-would live for an indefinite time if supplied hourly with about 28 litres or a cubic foot per hour of oxygen, for the nitrogen of the air is used over and over again. In the apparatus invented by Fleuss, this problem is partly accomplished; with the aid of the apparatus, which essentially consists of an ingenious respirator connected with a reservoir of oxygen and a rubber sponge saturated with caustic potash, a man may cut himself off entirely from the external air, and in this way descend into the ocean depths or into mines rendered dangerous from choke-damp. Operating under ordinary conditions, however, there are no means at hand to remove the impurities of the breath, and the only way which is found to answer is by enormous dilution. It is generally recognized that to keep the air in the highest degree of practicable purity, no less than 3,000 cubic feet per hour of air is required; this quantity is 600 times the amount of air spoilt. Multiplying then by 600 the cubic feet of air which the different animals render irrespirable, we get the following theoretical amounts of air which should be supplied per hour to animals: 1 The feeling of draught is not always produced by an actual current of air; if, for instance, a person should sit by a cold wall, there is a radiation of heat from the person's skin, causing the same sensation and the same effects as if blown upon by a current of cold air. 72 44 4 It has been already stated that carbon dioxide, although in small quantities in itself not injurious, nevertheless has such a close relationship with other impurities-the air pollution rising and sinking with the increase or decrease of the carbon dioxide-that its estimation is utilized as a measure of impurity. The standard Dr. Parkes adopted was 6 carbonic acid per 1,000 volumes of air. If this number is adopted, then the ventilation, to be successful, must not allow the carbonic acid to exceed this. Experiments were made both by Dr. de Chaumont and the late Dr. Parkes, in which they found the organic impurity of the air was perceptible when the carbon dioxide rose to 6 per 1,000 volumes (i.e. 0006 in each cubic foot). This standard is a high one, and difficult to attain, but experience has shown the correctness of Dr. Parkes's views, and the standard is now generally accepted. For the purposes of air supply the weight of a man may be taken as 140 lbs., which is the mean number of lbs., deduced from British statistics by Dr. W. Stephenson, for males of the labouring classes between the ages of 25 and 30; the average weight of the non-labouring classes is rather more, viz. 154 lbs. Using, however, the standard weight of 140 lbs., and taking 3000 cubic feet of air per hour as the proper amount, the quantity of air to be supplied will for other ages be proportional to the weight of the individuals; the average weight of children of 5 years of age is about 40 lbs., 10 years of age 66 lbs., and 15 years of age 105 lbs. ; hence we shall not be far wrong if the necessary air supply be stated as follows: Parkes and De Chaumont have given simple formulæ by which the amount of cubic feet of air to be supplied hourly so as to reduce the CO2 to any standard can be readily calculated. One of these is as follows:-Let e be the assumed quantity of CO2 exhaled by an adult male in an hour, viz. 6 cubic foot, r the ratio per cubic foot of air to which it is desired the CO2 should be reduced, and R the ratio of CO, naturally in the air, viz. 0004 per cubic foot. Then R required delivery of air per hour in r е = cubic feet. For example, let r be '0006, then .6 00060004 = 3000. If the standard of purity be taken not as 0006, but as 0009, then .6 = 1200 cubic feet to be supplied per hour. Or if the carbonic acid (CO2) in the air be determined by experiment, and the experimental number be substituted for r, the answer will give the amount of air which has entered and been utilized. Thus if in an experiment the CO2 in the air be ascertained to be 3.5 per 1000 volumes (i.e. 0035 in each cubic foot), then .6 1935 3 cubic feet of fresh air which have entered 00350004 = the room and been utilized. The amount of impurity in rooms, as estimated by the organic matter, the carbon dioxide, and the number of micro-organisms, varies inversely as the cubic space, as the following table' well shows: TABLE XIV. IMPURITY OF THE AIR OF SLEEPING-ROOMS IN RELATION TO CUBIC SPACE. Cleanliness tends to air purity; dirtiness of rooms to air contamination, as the table on the following page shows. (36) Atmospheric Impurity from Combustion. In our climate we pass a large portion of time by the aid of artificial light, and all artificial lights, with the exception of the electric, contaminate the air with carbon dioxide and sometimes other products of combustion; all these products ought to be led 1 On the Ventilation of Schools, by Sir Henry Roscoe. The results of both tables are based apparently on Carnelley and Haldane's researches. F into the outer air by special shafts, in this way assisting instead of rendering ventilation more difficult, but as this cannot always be done it is necessary to consider to what extent the air should be diluted to neutralize the product from gas, candles, petroleum and other sources of illumination. The amount of air-dilution to purify sufficiently the atmosphere polluted by gas or lamps need not be so great in relation to the carbon dioxide as in the case of breath impurity; it will be ample dilution if we supply 900 cubic feet of air for every cubic foot of carbon dioxide per hour evolved by the light, and as a cubic foot of coal gas properly burnt evolves about 2 cubic feet of CO,, for every cubic foot of coal gas allow 1,800 cubic feet of air per hour. The following table gives the amount per hour of carbon dioxide which it is stated are evolved when a sufficient quantity of each of the illuminants named is burnt to give a light equal to 20 standard candles : |