WARMING AND. VENTILATION. 



291 



draught may be increased or entirely produced in it by beating it by steam, 

 or by placing a steam-jet in it as in a locomotive. 



73. Wo7^kshops in icMch dust more or less dangerous to hreathe is pro- 

 duced. — In a large number of occupations, the division of the raw ma- 

 terials i)roduces dust, which may be fine or coarse, heavy or light, 

 harmless or injurious, and which it is important to remove from the 

 workman and carry out of the building. 



In most of these cases, ventilation, by means of a draught produced by 

 heat, would be insufficient, at least unless it were made extremely power- 

 ful by an intense heat. It would be sufficient for light dust of very 

 finely-divided materials, but for heavier dust, such as that produced by 

 grindstones, it becomes necessary to use mechanical apparatus to force, 

 through suitably-arranged pipes, currents of air at a proper velocity, 

 which trial alone can determine. 



In winter, when artificial heat maybe required, as well as in summer, 

 when it is unnecessary, it is essential that the discharge-openings should 

 be placed as near as possible to the machines which produce the dust or 

 emanations, and that the openings for admission of fresh air should, in 

 general, be far off, in order that the velocity should gradually increase 

 from the point of admission to that of exit. 



But if the shop contain few workmen, if it is naturally sufficiently 

 well aired, and if it is only required to carry off the dust as directly and 

 quickly as possible, it would be better that the air be admitted under the 

 cover which should completely surround the apparatus or the machine 

 above the point where the dust is produced, while the draught is applied 

 below the same point and the dust is carried directly out of the building. 

 The preceding remarks apply especially to those shops in which but 

 a few detached instruments are used. 



74. Cutlery-worlcs. — One of the most dangerous occupations is that of 

 the cutler. When proper i^recautions are not taken, the dust arising 

 from the grindstones, which are used dry, enters into the respiratory 

 passages. 



These dangers are reduced and almost removed by the following ar- 

 rangements: 



23, 24.) — The stones should be sur- 

 rounded as completely as possible 

 by a movable covering of wood or 

 sheet-iron, which should have no 

 opening in front but what is abso- 

 lutely necessary for the work. 



In order to avoid the choking-up 

 of the ventilating-pipes, it will be 

 necessary to provide special dis- 

 charge-pipes for tlie water, some- 

 what as indicated in the figures, according as the stones are partly 

 below or entirely above the floor. 



Grindstones used u'ct. 



