187 



v^kv kv^v^ (10) 



v + {h2 — h^T) h,T 

 Writing equation (10) with subscripts referring to the tube B Fig. 1, 

 as used in series II with nitrogen, at a temperature of liquid air, 



k,p\v\ (11) 



Dividing (11) by (3), 



k,p\v\ 4:n^,A,h,T, k, pvh,T,/-\ (12) 

 = ;^ whence ^ ^ 



kpV 4 71-/1.2 ^ p2^jj2^/2 



For normal conditions pv=^16 (l+nt), whence 



k^ L\ h, T, (13) 



k i^ p- 1 v'^1 



Ihe product pH'-c, referring as it does to nitrogen at liquid air tempera- 

 ture, must be computed from the empirical equation (7). Equation (13) 

 is used for the calculation of results for series II, given in table IV. 



Description of Apparatus and Method. — A general view of the ap- 

 paratus as mounted for use is shown in Fig. 1, the essential features of 

 which are shown in Fig. 2. Two glass tubes, A and B, Fig. 2, about 3.2 cm. 

 in diameter, were bent at right angles, about 30 cm. from the ends, the 

 horizontal portions being about SO cm. long. These were mounted on a 

 rectangular frame of wood, a a a a. This frame was hung with its plane 

 vertical, and was capable of rotation about a pivot at the point O. The 

 entire structure could be tilted forward slightly about an axis XX'. A 

 glass rod e f g, 100 cm. long, with enlarged ends, was clamped at points 

 i and f of its length from its ends, the supports for the rod at these points 

 being of rubber, and serving at the same time to close the ends of the 

 tubes. Through these rubber stoppers were passed small delivery tubes, 

 for introducing the gas used. Adjustable pistons, were inserted through 

 similar rubber stoppers at c and d. The upper tube was surrounded by a 

 double walled vessel made of tinned copper, and covered with a layer of 

 heavy felt. This vessel had a closely fitting double cover, provided with 

 mica windows through which the thermometers were read. It was also 

 provided with inlet, outlet and drainage tubes, so that steam could be 

 passed in and the temperature of boiling water indefinitely maintained 

 about the enclosed tube A. A long trough was made of such dimensions 

 that it could be raised up about the lower tube B, and when filled \vith 



