276 Unwersity Geological Survey of Kansas. 
values thus obtained by calculation from a volumetric analysis 
of a gas are subject to grave errors, which make them, at best, 
little better than mere approximations. It is so difficult to de- 
termine accurately the relative quantities of methane, ethane 
and higher hydrocarbons (see discussion of this point on page 
278) and there is such a large difference in the heating value of 
these substances that a relatively small error in the analysis 
will produce a large error in the calculated heat value, and 
thus vitiate the results obtained. In general, it may be said 
that a calculated heating value of a gas is only as reliable as 
the values for the amounts of the separate hydrocarbons ecal- 
culated from the analytical explosion data. 
The other method of obtaining the heating value is to actu- 
ally measure, in a properly devised calorimeter, the quantity of 
heat given off when a known weight or volume of the fuel is 
burned under standard conditions. 
For gases this is done by means of a gas-calorimeter. There 
have been devised several such instruments, but all possess 
somewhat similar construction and are based upon practically 
the same principles. Briefly stated, these are as follows: A 
carefully measured volume of gas at uniform and determined 
pressure and temperature is burned in the instrument in such 
a way that all of the heat given off during the combustion is 
transmitted to water, which is flowing under a constant head 
through the instrument. The rise of temperature of the water 
during its passage, multiplied by the weight of water passed 
through during the time of burning a unit volume of the gas, 
gives the amount of heat available from the combustion of the 
given volume of gas at the prevailing temperature and pres- 
sure, the water produced in the combustion being largely con- 
densed to liquid. 
If this value is to be compared with the heat value calculated 
from the analysis of the gas, it is necessary to subtract from it 
the heat given off by the condensation of the water formed in 
the combustion of the gas. Since the theoretical calculation is 
based upon volumes of gas measured at standard conditions of 
temperature and pressure, 0° Centigrade, and 760 millimeters 
pressure, the value determined by the calorimeter measure- 
ment must also be reduced to the same conditions. 
Many of the published results for determination of heat 
values do not state whether or not this correction has been 
made. We judge from the appearance of some of them that it 
