﻿Prof. E. Bunsen's Calorimetric Researches, 1 73 



- l grm. 



5 divisions of the scale, 



02 „ 



10 



t> 



» 



04 „ 



20 



t> 



>t 



0-6 „ 



30 



» 



i) 



0-8 „ 



40 



a 



if 



1-0 „ 



50 



a 



t» 



After one of these weights, heated under the tongue, has been 

 dipped in, the mercury- thread can be allowed to go back to the 

 desired mark. The great alteration on the scale caused by in- 

 troducing a weight only warmed to 37° C. is quite sufficient to 

 indicate the extraordinary sensitiveness of the instrument. The 

 elevation of temperature which 0*4 grm. brass at 37° C. caused 

 on dipping into about 20 grms. of water was found by the ther- 

 mometer to be only o, 07 C; while with the calorimeter just 

 described the variation amounted to 20 divisions of the scale, 

 each of which, in the instrument used, measured a millimetre. 



In reference to reading off on the scale, we have still to re- 

 mark that before each observation with the telescope it is neces- 

 sary (especially when the scale-tube is very narrow) to shake it 

 gently until the capillary resistance is overcome, and the mer- 

 cury-thread by further shaking does not alter its position. 



Table I. shows that the mercury-thread of the instrument was 

 not completely stationary. The alteration, which may amount 

 from 1 to 3 divisions in an hour, either in a positive or negative 

 direction, is nearly proportional to the time, as is easily proved 

 by using the calorimeter. The small error thus caused is re- 

 moved in the following way : — As soon as the observer sees that 

 the instrument has become stationary enough, he notes from 

 half-hour to half-hour the position of the mercury-thread. If 

 the alteration of the mercury amounts in m minutes to t scale- 

 divisions, then the deviation caused by disturbing influences is 

 for one minute 



The time M and the position of the mercury-thread Q are 

 now observed at the moment when the substance to be examined 

 is taken from the heating- vessel /, fig. 4, and dropped into the 

 calorimeter-vessel a, fig. 1. Both observations are repeated an 

 hour later, and M, and C^thus obtained, and lastly, once more, 

 as at the beginning of the experiment, the alteration of the mer- 

 cury-thread which is independent of the heat to be measured, 



m 



