W = weight of dry chimney gas per pound of coal. (D) Loss due to incomplete combustion of the carbon content of the fuel, that is, the burning of the carbon to CO instead of CO_{2}. 10,150 CO Loss in B. t. u. per pound = C×--------- (35) CO_{2}+CO C = per cent of carbon in coal by ultimate analysis, CO and CO_{2} = per cent of CO and CO_{2} by volume from flue gas analysis. 10,150 = the number of heat units generated by burning to CO_{2} one pound of carbon contained in carbon monoxide. (E) Loss due to unconsumed carbon in the ash (it being usually assumed that all the combustible in the ash is carbon). Loss in B. t. u. per pound = per cent C × per cent ash × B. t. u. per pound of combustible in the ash (usually taken as 14,600 B. t. u.) (36) The loss incurred in this way is, directly, the carbon in the ash in percentage terms of the total dry coal fired, multiplied by the heat value of carbon. To compute this item, which is of great importance in comparing the relative performances of different designs of grates, an analysis of the ash must be available. The other losses, namely, items 2, 5 and 8 of the first classification, are ordinarily grouped under one item, as unaccounted for losses, and are obviously the difference between 100 per cent and the sum of the heat utilized and the losses accounted for as given above. Item 5, or the loss due to the moisture in the air, may be readily computed, the moisture being determined from wet and dry bulb thermometer readings, but it is usually disregarded as it is relatively small, averaging, say, one-fifth to one-half of one per cent. Lack of data may, of course, make it necessary to include certain items of the second and ordinary classification in this unaccounted for group. TABLE 57 DATA FROM WHICH HEAT BALANCE (TABLE 58) IS COMPUTED