360 



Mr. J. Joly. 



If these be compared with the extremes contained in the table it will 

 be found that, except in the case of silver, the comparison is favour- 

 able to the method of condensation. 



At the suggestion of Professor Fitzgerald, experiments on distilled 

 water sealed in glass envelopes were undertaken. It appeared 

 probable that the specific heat of this substance, as obtained in 

 experiments made on a very large scale by Regnault, would afford 

 more reliable data for comparison than metallic solids, in the case of 

 which too it is likely that differences in molecular freedom may exist 

 affecting the calorific capacity to a considerable extent. Again it 

 was easy to obtain this substance sufficiently pure with facility. The 

 experiments were carried out as follows : — 



A very thin glass bulb is blown before the blowpipe. Its capacity 

 is to be some 15 or 20 c.c. In drawing off the tube, a little hook is 

 left for conveniently suspending the bulb in the calorimeter. It is 

 sealed by closing the extremity of the hook ; but before doing so we 

 see that no appreciable quantity of moisture is enclosed, introduced 

 from the breath in blowing it. If moisture is visible it is expelled by 

 repeated heating and cooling, the cooling finally being effected several 

 times in a desiccator. Neglect of this caused appreciable error in 

 some of my experiments ; it was ultimately detected in the abnormal 

 specific heat ascribed to glass by the initial experiments on the 

 envelope. It is probable that this trace of water, as suggested by 

 Professor Fitzgerald, and contrary to my original idea when ignoring 

 it, acts more by its latent heat of vaporisation than by its specific heat. 



To ascertain the amount of precipitation to be allowed for this 

 envelope, it is hung from a wire loop between the stirrups of the 

 carrier, so that condensation falling from it is received in the bucket 

 beneath. 



The total condensation for bulb and carrier together with that due 

 to the air contained in the bulb, including also the effect of displace- 

 ment difference from air to steam, afford — 



(1.) ^=0116. .... Range, IPO— 100'35° 



(2.) ^=0-116. .... Range, 11-3— 100-35° 



The bulb is now opened by removing the extremity of the glass 

 hook, and weighed == 2 -084 grams. The height of the barometer 

 (760) and temperature (11°) are noted. 



The next operation is to fill it with distilled water. This is effected 

 under the receiver of the air-pump by exhausting while the orifice of 

 the bulb is submerged, and again cautiously exposing to atmospheric 

 pressure. A space is left unfilled to allow for subsequent expansion. 

 The contents of the bulb are now raised to boiling point by immersing 

 in a bath of boiling water, and it is sealed with the blowpipe while 

 at this temperature. This is necessitated by the thinness of the 



