4 CALORIFIC POWER OF FUELS. 



other. The heat of combustion of one kilogram of hydrogen 

 being 34500 calories,* and the water formed being liquid at 

 o C., a portion of the 34500 calories is used to vaporize the 

 water in the case where it is gaseous or considered as such. 



Experiment has shown that the heat of vaporization of 

 water is expressed by the formula of Regnault, 



606.5 -(- 0.305^, or 

 1091.7 + o.3O5(/ 32) for Fahrenheit degrees, 



in which / represents the temperature of the water in the state 

 of vapor. Now one kilogram of hydrogen produces nine 

 kilograms of water. To keep these nine kilograms of water 

 in vapor, at 100 C. for example, there will be needed, by the 

 above formula, 637 calories per kilogram of water, or nine 

 times as much per kilogram of hydrogen, which is 5733 

 calories. These 5733 calories reduce to 5453 when the water 

 is considered as being at o C. instead of at 100 C. Deduct- 

 ing 5453 calories from 34500 calories representing the heat of 

 combustion of hydrogen, the water formed being condensed, 

 we obtain 29047, which number represents the heat of com- 

 bustion of hydrogen, the water being in the state of vapor 

 at o c . We will call it, in round numbers, 29ioof calories, as 

 is done by several writers. 



THERMOMETERS. 



Before taking up the study of calorimeters, we must con- 

 sider the calorimetric thermometer, which is a most important 

 part of the apparatus employed. The reading of the ther- 

 mometer and the corrections are quite delicate and also very 

 important, the calculation of the heat of combustion depend- 

 ing principally on their accuracy. 



In this work calorimetric questions relating to fuel only 

 will be considered; hence a description of ordinary ther- 



* 621008. T. U. f 52380 B. T. U. 



