On the Steam Calorimeter. 



223 



The volume, Y lt of the sphere at the temperature, t v of the air. 



V 2 , » „ t 2 „ steam. 



„ reading, p, of the barometer at the time of equilibrating the 

 sphere in air. 



„ „ P, of the barometer at the time of equilibrating the 



sphere in steam. 

 „ weight, w f added to the counterpoise during experiment. 



From these measurements, if D be the deduced density of dry air 

 at the temperature ^ and pressure jp, then the density, B, of steam 

 (weight of 1 c.c.) at the pressure P, is got by — 



a = _j-^ — 



This is a close approximation ; for if w Y , v^ represent the weight in 

 vacuo and the volume of the counterpoise respectively, when the 

 sphere is equilibrated in air ; w 2 , % the weight and volume of the 

 counterpoise when the sphere is in steam ; and if d be the density of 

 the air prevailing during this last period, and W = the weight of the 

 sphere in vacuo ; then first : — 



w x —v^D = W-VJ), 



secondly, w 2 —v 2 d — W— Y 2 B. 



Assuming i^D = v 2 d, as the difference between D and d will be 

 small or non-existent, and v 2 — v x is also small, and subtracting, 8 is 

 obtained as above. 



The details of eight experiments effected in this way are contained 

 in Table III. It is only necessary to observe regarding the data 

 of these experiments that V T and Y 2 were based on a measure- 

 ment of the volume of the sphere made by weighing it in air and 

 in distilled water in the usual way. After all corrections, the 

 volume was found to be 164*60 c.c. at the temperature 10*50. The 

 volume at the temperatures prevailing during the subsequent experi- 

 ments was in each case obtained from the formula of Matthiessen,* 



Y Ta = V Tl (Ji + a (T.-T0 + 6 C^-T^), 



where a = 4 ; 443 x 10" 5 , b = 5*55 x 10~ 8 . 



* ' Eoy. Soc. Proc.,' vol. 15, 1866, p. 220, 

 VOL. XLVII. S 



