292 



WARMING AND VENTILATION. 



FJQ.2^1- 



The passage intended for carrying off the dust should be placed un- 

 derneath the stone, and beyond the point where the work is applied, 



regarding the direction of the mo- 

 tion. It should have a breadth a 

 little greater than that of the stone, 

 and a depth of eight inches, at 

 most, for the largest stones. A 

 sliding door serves to close it when- 

 ever dry dust is not produced. 

 The water-discharge pipe should 

 also have a valve, which may be 

 closed when water is not used, and 

 when it is desired to carry off the 

 dust produced when the stone is 

 trued. 

 The separate air-tubes from each 

 stone lead to a collecting-pipe 16 inches by 12 inches, to which they are 

 united by couplings. 



If there are only four or live stones in the works, a single collecting- 

 pipe will be sufiQcient, and the blower should be placed at the end. But 

 if there are eight or ten stones in one line, it will be better to place a 

 second collector, 16 inches by 13 inches, in the middle of the length of 

 the first, and perpendicular to its direction. The blowing-apparatus 

 should be placed in the extremity of the second pipe. 



Finally, if there are two long parallel rows, with eight or ten stones 

 in each, they should also be connected with the second collector, or with 

 a third, 16 inches by 20 inches, communicating with the ventilator. 



In all these arrangements, movable valves should be placed at the 

 junction of each of the pipes, to prevent the circulation of air in those 

 which are not used at any time for carrying off the dust, since it is not 

 intended to ventilate at the same time all the stones of the same mill. 

 The valves "placed at the head of each pipe should also be closed when 

 it is not being ventilated. 



But the greatest difiQculty in rendering these places. healthful, as in 

 most other cases, arises from the carelessness of the workmen, and in 

 the negligence of the foremen, who do not insist on the strict observance 

 of the regulations. 



76. Ap2)lication. — At Chatellerault's armory, the results obtained by 

 Peugeot & Bros., of Yalentigney, (Doubs,) in their hardware manufac- 

 tory, were made use of, blowing-machines having been placed in two 

 shops containing each — 



Main stones, 8 inches in diameter 2 



Grooving-stones, 4 feet in diameter 16 



IS 



A fan-blower, 31 inches in diameter and 16 inches wide, parallel to the 



axis, and having a central opening 11 inches in diameter, making 900 



