February, 1845.] 203 



11. The performance of smith's work of a uniform character, such as the 

 manufacturing of chains by means of the several varieties of fuel. The number 

 of links of chain formed by a given weight of each coal, is here the measure of 

 useful effect. 



Tho object of the present communication is mainly to exhibit the relation 

 between the results obtained by the eighth, and thoso by the ninth method of 

 trial above mentioned. 



The existence, in bituminous coals, of variable proportions of nearly pure 

 charcoal, is referred to as furnishing evidence of a want of homogeneousness in 

 this class of bodies. A diversity of results may consequently be expected when 

 ultimate analysis is resorted to for the purpose of establishing a theory of trans- 

 mutations, or of demonstrating what changes have occurred in bringing vegeta- 

 ble substances into the state of bituminous coal. Thoso who assume woody 

 fibre as the sole basi3 from which it has been derived, do not pretend to prove 

 that the other proximate constituents of vegetables, the resinous matter, for ex- 

 ample, and the oily component of seeds, have been wholly removed. Hence 

 analyses of coal applied to this purpose may not always lead to unobjectionable 

 inferences. But as means of determining the calorific power of combustible 

 bodies, they may, especially when performed on average samples, or multiple 

 specimens, afford information both interesting to science and valuable to the 

 arts. 



The relation between the calorific power calculated from analysis, and the 

 practical heating power decided by evaporating water, is determined for 6ix 

 different varieties of bituminous coals, varying considerably in their composition. 

 Drawings of the apparatus employed for both these purposes were exhibited, 

 and their action explained. That used in evaporation is so constructed as to 

 determine the proportion of heat expended on the products of combustion, as 

 well as that employed to generate steam. 



In applying calculations to the ultimate analyses of coals as well as to the 

 products of combustion, the atomic weight of carbon is assumed to be six, of 

 oxygen eight, and of nitrogen fourteen times that of hydrogen, in accordance 

 with tho recent determinations of Dumas. In calculating evaporativo powers, 

 the latent heat of steam is taken at 1030° Fahr., according to Prof. J.'s own 

 investigations of that subject. 



In ascertaining the relative efficiencies and values of combustible bodies, with 

 a view to economical applications, it is necessary to take them either as found 

 in nature, or as supplied to commerce, including, of course, whatever impurities 

 they may chance to contain. But in order to deduce general relations between 

 bodies differently constituted, in regard particularly to their combustible con- 

 stituents, the comparison must be made after deducting the waste, or ineombus- 

 tible matter found in the crude state of the fuel. This principle is applied both 

 to the ultimate analysis and to the evaporative experiments ; and hence in the 

 following table both the calculated evaporative power of the carbon constituent, 

 (column 15,) and the total evaporative efficiency by experiment, (column 18,) 

 aro referred to, and calculated for, one part by weight of combustible matter. 



The relation between the fixed and the volatile combustible matters of coals, 

 is liable to considerable variation, according to the rate of distillation to which 

 they arc subjected. The more slowly this process is conducted, the higher (within 



