10 STEAM BOILER TESTS — ROBB. 



bustion of the fuel takes place and the heat produced is absorbed 

 by the water — the total quantity of heat being determined by 

 the rise in temperature of the water. This method has some ad- 

 vantages over an analysis, and, if care is exercised in the selection 

 of samples to be tested — or a large number of samples tested — is 

 perhaps the best means of establishing a theoretical standard 

 calorific value of a fuel ; but the quantity tested is necessarily 

 small, and may not fairly represent the fuel. It also leaves out 

 the heat absorbed by the non-combustible portions of the air and 

 fuel, which is an important factor in the combustion of fuel 

 under ordinary conditions. 



The method, by which the fuel is consumed under actual con- 

 ditions and in large quantities, in evaporating water in a steam 

 boiler is generally regarded as a test of the efficiciency of the 

 generator, rather than as a test of the value of the fuel ; but 

 somewhat extended observations of the performance of various 

 steam generatois, using similar grades of coal, has convinced the 

 writer that the steam boiler test, when properly conducted, is 

 quite as valuable as a means of determining the calorific value of 

 fuel, and of comparing various fuels, as for finding the eflficiency 

 of the generator — in fact, the latter is the more uncertain of the 

 two, because, unless a boiler is tested with fuel of a known calo- 

 rific value, it is impossible to arrive at its actual efticiency, or to 

 compare it fairly with any other form of generator. 



In testing the heat of fuel in an ordinary steam boiler, two 

 elements of uncertainty are introduced, viz, loss through imper- 

 fect combustion of the fuel, and the escape of gases at a higher 

 temperature than the atmosphere ; but as these losses, as well as 

 the heat absorbed by the non-combustible portions of the air and 

 fuel, are unavoidable in the present state of science, they should 

 be taken into account in making a practical test of fuel, and 

 strict accurancy only requires that the loss be uniform and mini- 

 mum in result. Practical experience teaches that almost perfect 

 combustion may be attained in any of the common forms of 

 steam generator by careful and regular stoking, with a properly 

 regulated air supply ; and, that this skill is possessed by many 

 ordinary stokers, who have no knowledge of the laws which 



