310 WARMING AND VENTILATION. 



The amount of beat passiug iu an hour through a glass ceiling or roof 

 will be given by the formula — 



C = K S (T - T') 

 Engineers only admit for the co-efficient K the value K = 1, while 

 the data obtained at Ferrieres seem to show that for a double glass cov- 

 ering — that is to say, a glass roof and a glass ceiling — it should have the 

 value K = 3, and for a single covering K = 4, especially as in the latter 

 case cold air might penetrate into the interior through the joints of the 

 glass. 



According to these values, allowing that the developed surface S' of 

 the roof is one and a half times that of the glass ceiling S, tlie amount 

 of coal to be burned in the coldest weather may be calculated as follows: 

 Let— 



S = 1,000 square feet; 

 S' = 1,500 square feet ; 

 The temperature of the external air be 14P ; 

 The temperature to be maintained within the roof be 113° ; 

 The temperature of the room, 59° : 

 The amount of heat passing off through the glass roof will be — 



C = 3 X 1500 (113 - 14) = ... 445, 500 units. 



The amount of heat passing off through the glass ceiling 

 will be — 



C = 3 X 1000 (113 - 59) = 162, 000 units. 



The amount of heat to be developed within the double 



roof = 607, 500 units. 



Admitting that the coke-stoves employed utilize, as is almost always the 

 case under similar circumstances, 90 per cent, of the heat given out by the 

 fuel, and that a pound of coke produces 12,000 units of heat, it is necessary 



to burn every hour — \ — . — = 53.57 pounds of coke an hour to prevent, 



•^ .90 X 12600 ^ 



under these almost extreme conditions of cold in Paris, the glass from 



cooling the room beyond 59°. At evening-receptions, the lighting-up of 



the room requiring a burner consuming 3^ cubic feet of gas an hour to 



every three square feet of floor-area, the heat produced will always be 



more than sufficient to prevent the cooling of the interior. 



The preceding figures show why most makers of heating-apparatus 



who have undertaken to warm halls or courts covered by sky-lights have 



only very imperfectly succeeded. 



DWELLING-HOUSES. 



103. Among the appendages of dwelling-houses which most often give 

 out disagreeable smells should be i)laced, in the first rank, yards, kitch- 

 ens, and privies. In consequence of the draught exerted by the chimneys 

 of rooms near these places, it often happens that at certain times more 

 or less infectious air is drawn into the apartments. 



