62 CALORIFIC POWER OF FUELS. 



p, the weight of the nitric acid, HNO,; 

 p\ the weight of the iron ; 



0.23 calorie, the heat of formation of I gram of nitric acid ; 

 and 1.6 calories, the heat of combustion of I gram of iron. 

 We then have 



g = (J + *)(/>+/>')_ (0.2 3 / + I.6/). 



In testing coal in this manner the small amount of sul- 

 phuric acid formed will be reckoned as nitric acid without 

 serious error, as it will be very small. The heat of the reac- 

 tion is 1.44 calories per gram of H a SO 4 formed. 



The above details apply to liquids as well as solids. Heavy 

 liquids, such as the heavy oils, tars, etc., are weighed directly 

 into the capsule ; but light, easily vaporized liquids must be 

 placed in pointed glass bulbs. These are put into the capsule, 

 and just before closing the bomb are broken to allow access 

 of the oxygen to the liquid. An almost perfect combustion 

 is obtained in operating with a great variety of materials, 

 nothing but cinders remaining. 



To determine the calorific power of gases the exact con- 

 tent of the bomb must be known. Fill it first with gas. 

 Then work the air-pump to reduce the pressure to several 

 millimetres of mercury, and then fill the bomb again with gas, 

 under atmospheric pressure and at the laboratory temperature. 

 The bomb may then be considered full of pure gas. 



The method of working with gases is the same as with 

 solids or liquids. The operator must not forget the need of 

 preventing too great dilution with oxygen, as then the mix- 

 ture will cease to be combustible. With illuminating gas 5 

 atmospheres of oxygen is sufficient, and with producer gas 

 only one-half atmosphere, as shown by the mercury gauge, is 

 needed. 



The gases to be burnt are kept in gas-holders over water 

 saturated with gas, or over salt water, according to circum- 



