470 THE MECHANICS OF VENTILATION. 



The mean of several tests was 705 heat-units per cubic foot of gas. We 

 ■will take, for purposes of calculation, 750 heat-units per cubic foot of gas. 



Gas burners range from three to six cubic feet consumption per hour, and, 

 •where no special arrangements are made for removing the heat and products 

 of combustion from the burnei'S, a simple calculation will show the great 

 influence upon the health of the occupants of an apartment exerted by this 

 apparently insignificant source of contamination. 



e. The production of carbonic acid from the lights. According to many 

 careful e^^periments the carbonic acid from a sperm or paraffine candle 

 equals 0.31 of a cubic foot per hour. Calculation based upon the average 

 «compositioe of coal gas shows that the combustion of a cubic foot of gas 

 produces 0.43 of a cubic foot of carbonic acid. Such a calculation stands 

 substantially as follows : Taking the average analysis of coal gas given 

 .above, we have by calculation from chemical equivalency the weight of 

 • carbon in a cubic foot of gas, and from this we derive the weight of oxygen 

 necessary to convert that amount of carbon into carbonic acid. The weight 

 vof the carbon, plus the weight of the oxygen, equals the weight of carbonic 

 :acid produced, and is found to be 343 grains. Density of carbonic acid gas 

 is 1.5 at a temperature of 60°. A cubic foot weighs at that temperature 801 

 grains, a cubic foot of air weighing 534 grains at that temperature. Divid- 

 ing the weight of a cubic foot of carbonic acid by the weight of that gas 

 ifrom a cubic foot of coal gas, and we have 0.43 of a cubic foot as the amount 

 of carbonic acid produced by the combustion of a cubic foot of coal gas. 



It is evident then that a considerable amount of oxygen is required for 

 the various processes of respiration and combustion going on in confined 

 spaces, and that a further deterioration of the air is continually taking place 

 toy reason of the presence of the nitrogen previously mixed with the oxygen 

 80 removed ; that is to say, oxygen the life-supporting agent in these various 

 processes is continually being removed, while nitrogen the inert, useless 

 element is left behind. Air in its normal condition contains twenty-three 

 per cent, by weight of oxygen, and seventy-seven per cent, of nitrogen. It 

 will soon result, however, in any confined space where respiration and com- 

 bustion are going on, that the amount of oxj^gcn constantly decreases while 

 nitoogea and carbonic acid increase relatively to the amount of oxygen 

 present. 



A farther source of contamination is found in insufficient sewer connec- 

 tions, though this part of the subject has been so often discussed that it is 

 juB&ecessary to consider it at length here. 



According to General Morin's paper on warming and ventilation, a trans- 

 lation of which appears in the annual reports of the Smithsonian Institution 

 for 1873-4, heating apparatus should be fuel considered in three different 

 respects : 1 — In regard to economy of fuel. 2 — In regard to effect on health, 

 3 — In regard to comfort. 



The nature of the service to be performed should always be considered 

 in deciding upon the apparatus for fulfilling those considerations. For in- 



