230 MESSRS.- W. R. BOUSPIELD AND W. ERIC BOUSFIELD 



12 Specific Heat of Glass. In the continuous-flow experiments the heat capacity 

 of the calorimeter does not come into the account, but in the experiments from point 

 to point of the range it is necessary to know the capacity. This has been found to 

 have a mean value of 595 "5 joules per degree, between 13 C. and 55 C. 



The assumption that this capacity would be substantially constant for the range 

 from C. to 80 C. seemed hardly justifiable, and a rough experiment showed a 

 probable variation of 3 or 4 per cent, within these limits. It was therefore decided 

 to make a more careful determination of the specific heat of the glass. For this 

 purpose the broken remains of a similar Dewar vessel (one of the same batch) were 

 taken and the fragments were enclosed in a string bag. The weight of glass taken 

 was 1000 gr. The weight of the string bag was 14 gr., the effect of which was 

 neglected. A small glass tube was inserted into the mass of glass fragments, so that 

 a thermometer could be readily inserted into the interior. 



The observations were made by observing the change produced in the temperature 

 of a given weight of water by the introduction of the mass of glass. The glass 

 was placed overnight, before each experiment, in a suitable Dewar vessel which was 

 kept in an air thermostat regulated at a temperature about a degree above laboratory 

 temperature. This was deemed necessary in order to secure that the temperature of 

 the glass should be uniform throughout, About 2^ litres of water was placed in a 

 Dewar vessel, which was closed by an obturator consisting of a copper box for 

 holding water at a suitable temperature. The construction of this obturator was 

 very similar to that of the platinum obturator described in Section 11. For the 

 experiments at the higher temperatures an electric heater was used in the obturator 

 so as to maintain the temperature of the obturator at about 10 C. above that of 

 the water in the Dewar in order to prevent deposition of moisture. The Dewar 

 vessel was immersed in a water-bath, the temperature of which could be regulated so 

 that (in conjunction with the obturator) steady conditions of temperature could be 

 maintained in the interior of the Dewar vessel. Temperatures were taken every 

 minute, so that accurate allowance could be made for any small steady variation. At 

 the higher temperatures the time required for lifting the obturator, inserting the 

 mass of glass, and replacing the obturator, was from 15 to 20 seconds. This 

 exposure of the contents of the calorimeter involved a small reduction of tempera- 

 ture, which was accurately ascertained, and a proper correction was made therefor. 

 The glass being in all cases at about laboratory temperature (15 C.) no correction 

 was considered to be necessary for the exposure of the glass in transferring it from 

 one Dewar vessel to the other. 



Four experiments were made with the water only slightly above the freezing-point. 

 These, together with the experiments at higher temperatures, are included in 

 Table VI., in which the first column gives the reference number of the experiment ; 

 the second and third columns the temperatures of the glass before and after the 

 experiment ; the fourth column gives, under the heading Ai0, the difference produced 



