WARMING AND VENTILATION. 295 



pounds of damp linen, in which 35 pounds of water remain after they 

 have been wrung. 



The evaporation of these 35 pounds of water is effected in an hour 

 by the consumption of about 11 pounds of coal. 



The temperature of the chamber is kept at 158°, and the amount of 

 air passing into the chamber varies from 35,000 to 42,000 cubic feet an 

 hour. 



Four chambers, with their 32 rods, are attended to by one woman, 

 who fills and empties them. 



According to the rules previously given, the 35 pounds of water 



evai^orated, requiring 35 x 1170 = 40950 units of heat, and the 11 



pounds of coal giving 159,000, the calorific effect of the apparatus is 



40950 

 equal to ^^j^ = .20. 



The same result was also obtained from some experiments made for 

 seven years at La Saltpetriere, in which, with a consumption of 6,415 

 pounds of coal, 18,940 pounds of water were evaporated, the calorific 

 effect in these experiments was found to be .24. 



POWDER-DRYING ROOMS. 



79. In the case of powdered materials spread out to a certain thick- 

 ness, it is often necessary to use blowers which drive the air under a 

 table, closed on all sides, the top of which is formed of wire-gauze, on 

 which the substances to be dried are placed. 



Thus, in powder-mills, the air driven under the gauze has ordinarily 

 a pressure measured by a column of water -^j. or J inch high, and a tem- 

 perature of 1120 to 140°. The thickness of the layer of powder varies 

 from i to 3 inches, according to its nature. The air is heated to the 

 proper temperature by means of water or steam pipes. 



Although, in such cases, blowers are most frequently used, the same 

 result may often be obtained by means of a well-regulated draught 

 alone. At the powder-mill of St. Chamas, a drying-room, warmed by 

 hot-water pipes placed under the table, and supplied with a chimney 

 containing a hot-water vessel to produce a draught, has worked satis- 

 factorily even in the case of blasting-powder containing 8 or 9 per cent, 

 of water. 



BARRACKS. 



80. The volume of air to be renewed every hour for each individual 

 being given at 1,000 cubic feet during the day, and 1,400 to 1,800 dur- 

 ing the night, the proportions and arrangements of the openings will be 

 determined by the preceding rules. 



But it is principally, and it may be said solelj^ during the night that 

 the ventilation of the barrack-rooms is necessary, since, during the day, 

 the soldiers are almost always out of it. 



The heating of these rooms during the day is intended only to enable 



