IN 7 V? OD UCTOR Y. 5 



mometers and their manufacture will not be needed. They 

 are usually bought all finished, and should be obtained only 

 from reliable dealers. 



Favre and Silbermann employed a thermometer of their 

 own design, divided into ^ degrees and graduated from 32 

 to o C. Each degree occupied about 0.3 inch. By means 

 of a cathetometer they read to y-J--^ of a degree. Their calori- 

 metric bath of 2 litres capacity was subjected to at least 8 

 elevation in temperature, and the quantity of substance 

 necessary to use at times exceeded 2 <\ 2 



grams. To lessen this amount of rise 

 in temperature and also the time of 

 combustion, they used longer thermo- 

 meters, with scales reading to -g-J or "' 



even to T -oV-g-- Scheurer-Kestner used -M* [\$ & 



a thermometer divided to ^ with his 

 Favre and Silbermann calorimeter. 



Since then they have been used gener- LU 



ally. Such thermometers are difficult 

 to work with, and require care in ma- 

 nipulation, and often a series of ther- 

 mometers or at least two with scales 



I I I o 

 in sequence are employed. If the 



initial temperature of a calorimetric 

 bath is found a little above the highest 

 graduation on the first thermometer, 

 and if the rise in temperature of the FIG. I.-METASTATIC 



1 HERMOMETER. 



bath amounts to two degrees, we must 



substitute the second one having for its lowest degree the 

 highest of the first. Besides the trouble of substitution, it 

 necessitates a correction for agreement of the degrees common 

 to the two instruments. To obviate this difficulty the 

 " metastatic " thermometer was invented by Walferdin and 

 described in the Comptes Rendus de T Academie des Sciences, 

 1840, p. 292, and 1842, p. 63. 



