538 MR J. Y. BUCHANAN ON 



it arrives at the maximum temperature almost simultaneously with the first exit of 

 steam from the apparatus ; but that part of the steam tube situated above the exit tube 

 is not yet thoroughly warmed through, and a little time must be allowed during which 

 t he strength of the steam current increases until it becomes steady. In ordinary cir- 

 cumstances the apparatus cannot be held to be warmed through in less than 90 seconds, 

 and, for purposes of heat calculation, we take the initial period of heating to be two 

 minutes, during which it may be said always to be complete. Experiments made with 

 boiling mixture tube, weighing with thermometer 239*65 grms., showed the following 

 results : — 



Steam condensed, .... grms., 8*3 8-3 8-5 8-35 



In time, seconds, 85 90 100 90 



From these we find the mean amount of steam condensed in the first 90 seconds 

 8 '25 grms. When the steam was passed through for exactly two minutes before 

 weighing, the following weights of steam were condensed : — 9'1, 8'9, and 9 - grms., or 

 a mean of 9*0 grms. 



For vessels of the same pattern and nearly the same size the quantity of steam 



required to heat them or to keep them hot depends simply on the amount of 



glass. 



Thus, our apparatus weighs 239*65 grms., and may be considered to be all glass. If 

 the specific heat of the glass be 0*2, then the amount of water thermally equivalent to 

 it is 48 grms. In order to raise the temperature of 48 grms. water from 15° C. to 

 100° C, we require 4080 g° C. (gramme-degrees-Celsius), and this can be supplied by 

 7 61 grms. steam saturated at 100° C, and condensing at 100° C. But the mean tem- 

 perature of the apparatus during warming may be taken to be 5 7 '5° C, and the 7 "61 

 grms. water formed would, in cooling from 100° C. to 57*5° C, give out- 323*4 g° C, a 

 quantity which is furnished by the condensation of 0'603 grm. steam at 100° C. 

 Deducting this from 7*61, we have 7*007, or 7 grammes as the least amount of steam 

 required to raise the temperature of the apparatus instantaneously to 100° 0. In 

 practice, the operation takes a minute and a half, during which the apparatus is losing 

 heat at an increasing rate. This is supplied by additional steam condensed. We have 

 seen that the steam condensed in two minutes is 9*0 grms., and in 1^ minutes 8*25 grms., 

 Q-ivinsc 0*75 erm. of steam condensed in half a minute, or 1*5 arms, in one minute after 

 the whole apparatus has taken the temperature of 100° C. The mean temperature 

 during heating has been taken as 57 '5° C, so we may take the rate of cooling at -,% of 

 the above rate, or equivalent to the condensation of 0*9 grm. steam per minute, or ol 

 1*35 grms. for 1^ minutes. Adding this to 7 grms., the weight of steam required for 

 instantaneous heating, we obtain 8*35 grms. as the theoretical weight of steam required 

 to warm the apparatus under the above conditions. The mean observed amount is 8'2:> 

 grms., which may therefore be accepted with confidence. Also, we may confidently 





