196 MAXKLEIBER 



To avoid corrections for heat leakage some bomb calorimeters are 

 supplied with so-called adiabatic jackets, that is, jackets that may be 

 heated in an attempt to make their temperature equal to the tem- 

 perature of the calorimeter water. Such jackets are especially suit- 

 able for measuring uniform continuous thermal processes such as the 

 heat evolved by a radium preparation, or during the hardening of 

 Portland cement. For the abrupt heat production of explosions, 

 however, such as those in the calorimeter bomb, the advantage of an 

 adiabatic jacket is doubtful. Even with adequate stirring of the 

 jacket water and accurate measurement of its temperature, it is dif- 

 ficult to make the temperature of the inner jacket surface always 

 equal to that of the outer surface of the calorimeter bucket. Some 

 of the commercially obtainable bomb calorimeters have adiabatic 

 jackets even without stirrer. The loss in reliability introduced in 

 bomb calorimetry mth such devices seems a rather high price for 

 avoiding some simple calculation of temperature loss. 



8. Microcalorinietry 



Microcalorimetry deals with small thermal effects. In contrast to 

 microchemistry, relatively large amounts of material may be involved 

 in these measurements. Microcalorimeters may therefore be rather 



TABLE III 



Characteristics of Microcalorimeters 



Inventor 



Characteristics Ward Hill Lange Whipp {26) 



Water equivalent of heat 



system, g 50 0.6 1000 1 



Number of thermocouples 



of main thermometer .. . 31 150 1100 5 



Temperature sensitivity, 

 °C./inm. galvanometer 

 deflection 4 X 10"^ lO'^ 0.6 X 10-« 3X10-6 



Heat sensitivity, cal./mm. 



galvanometer deflection . 2 X lO'^ 0.5 X 10-« 0.6 X IQ-^ 3X10-6 



Resistance of galvanom- 

 eter, ohms 8.5 25 25 1 



Resistance of thermo- 

 couples, ohms 11.5 50 75 1 



Sensitivity of galvanom- 

 eter, amp. /mm. deflec- 

 tion 3.5X10-9 3.3X10-1" 10-9 3Xl0-i« 



Insulation of couples Organic Organic Organic Glass 



