1892.] the Sensitiveness of Safety-lamps. 89 



gases heated by the burning of the lamps tended by their lightness 

 to remain near the roof of the chamber, and were, therefore, only 

 gradually removed by a process of dilution with fresh air. 



The renewal of the atmosphere in the interior of the apparatus is 

 now effected by a much more certain and simple means. 



An opening is made in the roof of the chamber, immediately over 

 the large aperture in the floor, and corresponding to it in size. This 

 upper opening is closed with a water-seal, as in the case of the lower 

 one. To effect this a square trough of sheet zinc, about 2 inches in 

 depth, is fitted closely against the edge of the aperture, and a weighted 

 deep-edged lid dips into water, which nearly fills this trough. By 

 bedding a broad flange of this trough with red lead upon the top of 

 the chamber, screwing down broad wooden strips upon the flange, 

 and brushing the surface over with melted paraffin- wax, an air-tight 

 joint was at once obtained (see fig. 2). 



The replacement of the atmosphere in this modified chamber is 

 effected by removing the water-seals from both the upper and the 

 lower openings. The chamber, after having been used in an experi- 

 ment, is then found to be filled with fresh air after simply being- 

 allowed to stand for a few minutes. The replacement of the atmo- 

 sphere within the chamber may be secured in the course of a few 

 seconds by swinging the flap up and down several times. By this 

 means not only is the introduction of the fresh air much more rapidly 

 effected than by the use of bellows, but the complete removal of the 

 gaseous mixture filling the chamber is secured with certainty. 



"Fia. 3. 



