38 CALORIFIC POWER OF FUELS. 



from the bell-glass by metal springs, and intended to insulate 

 the crucible and prevent too quick cooling ; m is a glass jar 

 containing 2000 grams (4.4 Ibs.) of water, forming the calori- 

 metric bath. Water cannot enter the bell h while the cock / 



FIG. ii. W. THOMPSON CALORIMETER. 



is closed, and it is opened only when the pressure in the 

 gas-holder is sufficient ; n is a glass jar filled with water and 

 surrounding the calorimetric jar, and / is the agitator. 



One gram of fuel is put into the crucible, and on this is 

 placed a small cotton wick impregnated with bichromate of 

 potash. This is lighted at the instant of putting into the jar, 

 and its combustion aided by the oxygen kindles the fuel. 



This is an imperfect apparatus, and will give in most cases 

 only unsatisfactory results. Still it is in rather common use 

 in the shops of England, where it serves principally as a com- 

 parative measure, the errors being -considered constant. 



BARRUS'S CALORIMETER. 



The Barrus calorimeter is a modification of the one just 

 mentioned. While it requires considerable care in using to 

 get correct results, yet it is one of the simplest and most in- 

 expensive. 



