Heating Value of Gaseous Fuels--The method of computing calorific values from an ultimate analysis is particularly adapted to solid fuels, with the exceptions already noted. The heating value of gaseous fuels may be calculated by Dulong's formula provided another term is added to provide for any carbon monoxide present. Such a method, however, involves the separating of the constituent gases into their elementary gases, which is oftentimes difficult and liable to simple arithmetical error. As the combustible portion of gaseous fuels is ordinarily composed of hydrogen, carbon monoxide and certain hydrocarbons, a determination of the calorific value is much more readily obtained by a separation into their constituent gases and a computation of the calorific value from a table of such values of the constituents. Table 37 gives the calorific value of the more common combustible gases, together with the theoretical amount of air required for their combustion. TABLE 37 WEIGHT AND CALORIFIC VALUE OF VARIOUS GASES AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE WITH THEORETICAL AMOUNT OF AIR REQUIRED FOR COMBUSTION +---------------+----------+------+-----+------+----------+-----------+ | Gas | Symbol |Cubic |B.t.u|B.t.u.|Cubic Feet|Cubic Feet | | | | Feet | per | per | of Air | of Air | | | |of Gas|Pound|Cubic | Required | Required | | | | per | | Foot |per Pound | Per Cubic | | | |Pound | | | of Gas |Foot of Gas| +---------------+----------+------+-----+------+----------+-----------+ |Hydrogen | H |177.90|62000| 349 | 428.25 | 2.41 | |Carbon Monoxide| CO | 12.81| 4450| 347 | 30.60 | 2.39 | |Methane |CH_{4} | 22.37|23550| 1053 | 214.00 | 9.57 | |Acetylene |C_{2}H_{2}| 13.79|21465| 1556 | 164.87 | 11.93 | |Olefiant Gas |C_{2}H_{4}| 12.80|21440| 1675 | 183.60 | 14.33 | |Ethane |C_{2}H_{6}| 11.94|22230| 1862 | 199.88 | 16.74 | +---------------+----------+------+-----+------+----------+-----------+ In applying this table, as gas analyses may be reported either by weight or volume, there is given in Table 33[36] a method of changing from volumetric analysis to analysis by weight. Examples: 1st. Assume a blast furnace gas, the analysis of which in percentages by weight is, oxygen = 2.7, carbon monoxide = 19.5, carbon dioxide = 18.7, nitrogen = 59.1. Here the only combustible gas is the carbon monoxide, and the heat value will be, 0.195 × 4450 = 867.75 B. t. u. per pound. The _net_ volume of air required to burn one pound of this gas will be, 0.195 × 30.6 = 5.967 cubic feet.