188 



THE AMERICAN MONTHLY 



[October, 



rods at any given height. The iron 

 rods should be about 36 inches high, 

 being held in their places by a frame- 

 work that rises on the back part of a 

 wooden platform which rests upon 

 the taBle (or may be built into the 

 wall, or placed between two shelves 

 far enough apart in a closet in the 

 laboratory), and serves as a con- 

 venient place for any accessory ap- 

 paratus or instruments. 



The funnels referred to above, are 

 connected at the bottom of each by 

 a rubber tube, and have stop- 

 cocks above the points where the 

 tubing is attached. The opening 

 at the upper part of these funnels 

 is closed with rubber corks, through 

 which a glass tube is placed after 

 having been once bent at right 

 angles. 



The means of se- ^^j^ .■if^ 



curing the operation jT^fim \ 

 of the currents of air, 

 in such a manner as 

 to perform their work 



of which it forms a part has been 

 connected with the glass tube at the 

 top of the filtering funnel, from which 

 the air is forced by the flow of the 

 mercury to it from the other funnel, 

 which should occupy a higher posi- 

 tion. It also affords the means of 

 allowing a current of air to flow to 

 the surface of the mercury in the 

 higher vessel, through the other stop- 

 cock which should be turned so as to 

 afford ingress to the air ; this will be 

 secured when the s^'op-cock is placed 



Constant Pressure Injection Apparatus. 



properly, is an arrangement of three- 

 way stop-cocks of a peculiar con- 

 struction. These stop-cocks are each 

 so constructed that when turned in 

 one position they have the form of a 

 regular spigot, while, by a quarter 

 turn from that position, a straight 

 connection is made through the body 

 of the stop-cock to a tube opening at 

 that point. 



Two of these stop-cocks are placed, 

 one on each of the upward branches 

 of a glass tube having the form of the 

 the letter Y. This arrangement 

 affords the means of transmitting a 

 current of air under pressure through 

 that stop-cock which may be turned 

 so as to open a straight connection 

 through it, when that branch of the Y 



in a position at right angles to that of 

 the first described stop-cock. This 

 branch of the Y-tube should be con- 

 nected with the tube at the top of the 

 other filtering funnel. The lower 

 branch of the Y-tube should be con- 

 nected with the short arm of the bot- 

 tle containing the injection mass. 



All the joints made with the tubing 

 should be securely wired, and all the 

 other connections made as tight as 

 possible. 



The Y-tube described above should 

 be securely supported by extension 

 test-tube clamps, attached to the iron 

 rod to which the stationary filtering 

 funnel has been fixed, and below the 

 funnel. 



The long arm of the bottle con- 



