On Steam and Brines 165 



mean temperature of the apparatus during warming may be 

 taken to be S7'S C., and the 7*61 grms. water formed would, 

 in cooling from 100 C. to S7'S 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 7'6i, we have 7*007, 

 or 7 grammes as the least amount of steam required to raise 

 the temperature of the apparatus instantaneously to 100 C. 

 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 i minutes 8*25 grms., giving 075 grm. of steam con- 

 densed in half a minute, or 1-5 grms. in one minute after the 

 whole apparatus has taken the temperature of 100 C. The 

 mean temperature during heating has been taken as S7'S 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 of i'35 grms. for i| 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 8^25 grms., which may therefore be 

 accepted with confidence. Also, we may confidently calculate 

 the amount of steam required to warm another apparatus of 

 the same type on the basis of its weight. 



In order to determine more carefully the amount of steam 

 required to keep the apparatus at a temperature of 100 C. 

 during some time, two experiments were made, the apparatus 

 being dry and cold to begin with. In the first, steam was 

 passed through for 12 minutes, when 22*2 grms. were con- 

 densed ; in the second, the steam was passed for 32 minutes, 

 when 50-8 grms. were condensed. Allowing that in each case 

 9 grms. of steam were condensed in the first two minutes, we 

 have I3'2 grms. condensed in 10 minutes, and 41*8 grms. in 

 30 minutes. The first is at the rate of r32 grms. per minute, 

 and the second at the rate of 1-39 grms. per minute, or a 

 mean of i'35 grms. per minute. 



Experiments of a similar kind were made with NaCl, or 



