On the Steam Calorimeter. 



219 



" Steam Calorimeter " (as lie has designated it) and in my own 

 papers (Zoc. cif.), I will go over this old ground only so far as to be 

 intelligible to those who have not seen those papers. 



Theory of the Method. — The theory of the method is, briefly, as 

 follows : — A substance at the temperature, t u of the air brought into 

 an atmosphere of saturated steam will, in attaining the temperature, 

 to, of the latter, condense a certain weight of steam, w, such that w\ 

 where \ is the latent heat of vapour of water, represents a quantity 

 of heat equal to the calorific capacity of the substance between the 

 limits of temperature. Hence, if S be the specific heat of the body, 

 W its weight, 



w\ =ws (* 2 °-V) (i.) 



From this S is deduced by measuring w, t 2 °, ti°, W, and knowing the 

 value of X from recorded experiments. 



The apparatus required is one permitting the sudden admission of 

 steam around the substance, and subsequently the accurate observa- 

 tion of the weight of water precipitated upon it. 



The steam calorimeter is on the lines of a slight metal receptacle, 

 placed beneath a delicate balance, so that a wire depending from one 

 arm of the balance sustains a light wire platform within the re- 

 ceptacle or calorimeter. The platform is provided with a little 

 platinum-foil catchwafcer beneath it. The substance to be dealt with 

 is placed upon the platform. Steam being admitted into the calori- 

 meter, the substance rapidly rises to its temperature, condensing 

 steam, which adhering as water to its surface, or dropping into the 

 catchwater beneath, is estimated without loss by the balance. In 

 this way the value of iv is determined in the equation for the specific 

 heat. 



The observation of t° is effected by a thermometer left in company 

 with the substance in the calorimeter a sufficient length of time and 

 read just before admitting steam. The temperature of the steam, £ 2 °, 

 is deduced by inserting a thermometer in the calorimeter when it is 

 filled with steam or by observation of the height of the barometer. 

 In the thermometry it is sufficient in order to secure a high degree o£ 

 accuracy to read the second place of decimals by estimation, the ther- 

 mometers having a fairly open scale divided to tenths of degrees. 

 The range obtaining is so considerable that one tenth of a degree is 

 a small fraction of the whole. 



On the Values of the Constants required and the Corrections necessary 

 in the Use of the Calorimeter. 



The succeeding pages contain a discussion of the constants re- 

 quired in the use of the steam calorimeter and the mode of applying 

 the necessary corrections. 



