1891.] Heat produced by compressing liquids and Solids. 137 



taken, and the cycle of operations repeated. In this way three to 

 four substances per hour could be finished, from ten to fifteen ob- 

 servations being taken for each. The limits of accuracy are found in 

 the measurement of pressure, which cannot be said to be quite satis- 

 factory, and in the impossibility of maintaining the pressure perfectly 

 constant till the. galvanometer can be read. The error due to the 

 last-named cause is less than might be expected, because the pressure 

 varies rapidly about the point at which it should be maintained, and 

 the galvanometer does not follow the small and quick rises and falls 

 of pressure. In comparing the results among themselves the actual 

 amount of pressure is not of so great importance as the fact that, as 

 nearly as the gauge would read, it was the same in every case, viz., 

 2'6 tons on the sq. in. = 388 atmospheres. 



In order to show the degree of accuracy for this work, the full 

 figures for one substance are here quoted from the experiment 

 book : 



Substance taken, butyric acid. Pressure, 2'6 tons. 



Zero point. Beading. Deflection. Else of temp. 



17-0 11-8 5-2 523 



17-7 12-5 5-2 5-23 



ls-1 13-1 5-0 5-03 



18-6 13-3 53 5-33 



18-8 13-7 51 5-13 



19-0 13-7 5-3 5-33 



18-9 13-65 5-25 5'28 



19-1 13-9 5-2 5-23 



191 13-8 5-3 5-33 



19-3 14-1 5-2 523 



Average deflection 5' 205 



,, rise of temperature 5*235 



When the individual figures vary so little among themselves it will 

 easily be seen that the average of ten such observations must differ 

 extremely little from the truth. 



At the end of each day's work the junction was graduated to 

 ascertain what deflection of the galvanometer corresponded to a degree 

 centigrade. The graduation was performed ici the following 

 manner : The junction was drawn out of the gun and dipped in a 

 beaker of cold water from the tub to find its zero. As soon as the 

 galvanometer had been read the junction was transferred to a beaker 

 of warm water which was kept rapidly moving by means of a stream 

 of air, and the temperature and the galvanometer were read as nearly 

 as possible at the same moment; the junction was then again placed 



