342 MR. J. B. HANNAY ON A NEW CALORIMETER. 



XXX. On a New Calorimeter. By J. B. Hannay, F.R.S.E., 

 Assistant Lecturer on Chemistry, Owens College. 



Read March 19th, 1878. 



Having been desirous some time since of making a 

 number of calorimetric determinations, I set about con- 

 structing an instrument for the work ; but I found that 

 working in the rapid irregular manner in which I was 

 compelled to do by using only odd leisure moments, the 

 difficulty of obtaining a perfectly constant temperature 

 was very great ; and as I have, in a great measure, over- 

 come that difficulty, I think that an account of the 

 instruments which I have constructed may be of some use 

 to workers who may be placed in such a position as mine, 

 and may desire to make measurements quickly and without 

 waiting until the temperature is quite constant. 



In the first place, it is evident that, as the external or 

 accidental variation of temperature of the instrument is 

 generally not more than 0"2 to 0*3 of a degree, if the 

 internal variation be made greater in one case than 

 another the error arising from accidental variation will be 

 smaller. Now, if we use a liquid body to expand as an 

 indicator, we must, if we want a large rise of temperature, 

 use a small quantity of the liquid or a large quantity of 

 the body experimented with ; either of these conditions, 

 however, involves difficulties of a kind nearly as bad as 

 the temperature-variations. But if we use a gas as our 

 index — that is to say, if we use an air-vessel into the 

 middle of which we plunge the substance whose specific 

 heat we wish to determine, and have the vessel surrounded 



