458 On an Improved Form of Coal- Calorimeter. 



usual ways ; it is, however, necessary to ensure the constancy 

 of temperature o£ the stream of oxygen passing through the 

 instrument. When the supply is taken from a cylinder the 

 gas is apt to be cold, and should be passed through a 

 coil of tubing to attain the temperature of the room, and 

 finally bubbled through a wash-bottle containing a thermo- 

 meter to ascertain its temperature and to saturate it with 

 moisture. 



A certain amount of heat is introduced into the calorimeter 

 by the electric ignition ; this may be kept constant by always 

 using the same strength of current for the same length of 

 time, and the correction may then be eliminated by using the 

 same current when calibrating the instrument. The author 

 prefers to do this by burning in it a known weight of a 

 substance whose calorific value is known, and deducing the 

 water-equivalent of the whole from the rise of temperature 

 observed ; by slightly adjusting the water-contents the 

 water-equivalent may then be brought to round numbers, 

 thus saving much time in calculations. The substance used 

 by the author is pure carbon, such as obtained from sugar, 

 and the heating value is calculated from an elementary 

 analysis. Cakes of such carbon may refuse to ignite in 

 the instrument, but this can be overcome by adding a 

 small but known weight of some such substance as stearic 

 acid, which ignites readily and starts the combustion of the 

 carbon. It has been suggested to calibrate these instru- 

 ments by the combustion of such organic bodies alone, but 

 the author finds that they will not burn satisfactorily in this 

 instrument. 



As an alternative method of calibration a known amount 

 of heat may be introduced into the calorimeter by means 

 of the electric ignition device, but the author does not 

 regard this as anything more than a check upon the other 

 calibration. 



From the above account of the present instrument it will 

 be seen that no novelty of principle is claimed for it ; but 

 the author believes that the modifications of design and 

 method of use which he has introduced will allow the old 

 principles to be applied to greater advantage, and will render 

 this type of calorimeter more convenient to use and more 

 accurate and certain in its results. 



