RELATION OF AIR TO THE HOUSE WE LIVE IN. 211 



amount of the acid in the external atmosphere, we can calculate how 

 much of the latter must go on mixing itself with tlie room-air, to 

 which carbonic acid has been added, in order that the proportion of 

 the acid may decrease by so and so much in a definite time. The 

 action of diffusion or absorption may generally be left out of con- 

 sideration in this calculation. I do not consider this method to be 

 absolutely correct, but I have found it quite satisfactory when a 

 building was a few years old, and quite dry. At all events, until a 

 better method has been found, we must keep to this one, even if it 

 were still less complete than it is. 



By researches which are too complicated to lie explained in a pop- 

 ular lecture, it has been found that the ventilation of the same room 

 or space, when the doors and windows are shut, undergoes considera- 

 ble and definite alterations under diflerent circumstances. Ventilation 

 has been found to be much greater than had been supposed before. 

 On an average, in spaces in which the air kept good, there existed a 

 ventilation of more than 2,100 cubic feet per head and hour. It is 

 known that a person does not inhale and exhale more tlian eighteen 

 cubic feet of air per hour, and so it was thought that 2,100 cubic feet 

 per hour was a ridiculously large quantity for one person. 



But it has been shown, first in France, not by calculation, but 

 quite empirically by simple experimenting, that this quantity of ven- 

 tilation is not more than is absolutely indispensable. After the epi- 

 demic of cholera of 1848, the erection of a model hospital in the Fau- 

 bourg Poissonniere was decided upon, and the Hopital la Riboisiere 

 was erected, which was to be furnished with artificial ventilation. 

 The quantity of air which was required from the ventilating appara- 

 tus was stated in the plan. It was believed that the demands put 

 under Nos. 4, 5, and V, of the plan for ventilation, were extraordinarily 

 large : 



4. Continuous ventilation of warm air in winter and cold air in 

 summer at least 700 cubic feet per hour and bed in the large wards. 



5. Ventilation during the day only at 350 cubic feet per bed in the 

 rooms of the corresponding pavilion. 



7. The ventilating apparatus must have a surplus of strength, in 

 order to be able to produce in all or some wards a ventilation double 

 that stated. 



The air was partly propelled by fan-wheels, partly by ventilating- 

 flues. It flowed to and fro through pipes in the wards, and its veloc- 

 ity could be measured easily by anemometei-s. 



In preliminary experiments, a ventilation of 350 cubic feet per bed 

 and hour was tried, but the air was found already by the smell to be 

 so bad that the authorities congratulated themselves in having pro- 

 vided for double the strength. This was now tried, but with the 

 same result, and it w^as a comfort to know that, for extraordinary 

 cases, another 700 cubic feet per bed and hour could be obtained ; but 



