On the Steam Calorimeter. 



229 



thing like an effect due to mechanically suspended water in the steam. 

 It appears, in fact, to arise from a slow loss of heat from the substance 

 to the walls of the calorimeter, steam, in consequence, condensing on 

 the substance. 



The numerical results of my own experiments, effected in a large, 

 single-walled calorimeter of spherical form, 14 cm. in diameter, are 

 such as to afford : — 



3 milligrams per hour on a clean, blown glass sphere having a 

 surface of 80 sq. cm. 



4 milligrams per hour on a dull surface of platinum of 80 sq. cm. 

 8 milligrams per hour on a lamp-black coated surface of 



80 sq. cm. 



These results were obtained using a roomy calorimeter. 



From experiments in a calorimeter of the type to be presently 

 described, but somewhat smaller (8 cm. in diameter) and double- 

 walled only on the lower, removable part, I take the following : — 



(1.) A clean, but not bright, copper box, cylindrical in form, 

 having an external surface exposed to the steam of 52 sq. cm. 

 nearly, standing in a platinum-foil catchwater, exposing an effective 

 surface of 57 sq. cm. ; total 109 sq. cm. of clean metal, showed 

 j.n increment of from 0*45 to 0*5 milligram per 5 minutes. Thus 

 successive observations of the increment every 5 minutes afforded : — 



0-4 0-5 0-4 0-4 0-4 0-5 0-5 05. 



The inside of the calorimeter in this experiment was smooth and 

 clean. Later I made the experiment of gilding and burnishing the 

 inside surface of the calorimeter. This appeared, however, to make 

 no sensible difference : thus, with all otherwise as above, observations 

 gave the increment per 5 minutes : — 



0-5 0-5 0-5 0-5 0-5 0-5. 



(2.) A rough block of cryolite weighing 37 grams, resting on the 

 platinum catchwater as above, gave 0*74 milligram per 5 minutes ; 

 the observations were : — 



0-7 0-8 07 0-8 0-7. 



(3.) The catchwater of platinum foil alone, with stirrup, as 

 described in (1), in the calorimeter previous to gilding its interior 

 gave the increment, determined every 5 minutes : — 



02 0-3 0-3 0-4 0-3 0'4 0-5 0-3 

 0-3 0-4. 

 Mean increment, 0'34 per 5 minutes. 



