GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. xi 



at will for carbonic acid gas, without interfering with the ob- 

 servation, and at the same time the hands are left free for any 

 manipulation that may be requisite. A second apparatus, the 

 so-called DEVILLE'S, is arranged for the preparation of hydrogen 

 beneath my table in the same manner as that above described. 

 I use this gas as an indifferent medium; and as it passes through 

 a wash flask, mingle with it various vapours, as those of ammo- 

 nia, chloroform, etc. The mixture is accomplished by the aid 

 of a bag, which can be compressed with the foot, and from 

 which a tube conducts into the wash flask. If the effect of 

 pure hydrogen gas is desired to be seen, the above-mentioned 

 gas chamber is insufficient. Kiihne, to whom we are indebted 

 for making the first investigations with gas chambers, employs 

 a mercurial valve. Adopting this principle, I take a slide made 

 of hard caoutchouc, which is perforated in the middle, and to 

 the surface of which a glass plate is cemented ; or, which comes 

 to the same thing, I take a ring of hard caoutchouc, and cement 

 it to a glass plate. A groove is now made round the perforation, 

 which can be filled with mercury. The cover glass must then 

 be cemented to a little cell (fig. in. 6.) 



Fig. in. 



III. a. 



jr \ 



A II. 



A I. 



III 



Fig. in. a, Gas chamber, with mercurial valve, natural size. A I, bird's- 

 eye-view ; A II, longitudinal section through the middle line; n n, groove ; 

 //, clips ; gr, gas tubes ; r, object ; dd, covering glass in section. Fig. iii. 6, 

 covering glass. 



The object is placed on the inner surface of the cell thus 

 formed, and the lateral walls of the cell are placed in the groove, 



