202 [February, 1845. 



The Committee to whom was referred a communication by 

 Prof. Johnson, read at the meeting of the 11th inst., reported 

 in favour of publication. 



Prof. Johnson first states some of tho methods which have been hitherto em- 

 ployed by Chemists and others, to ascertain the relative heating powers of fuel. 



1. The heating of water, without converting it into vapour, as practised first 

 by Rumford, and more recently by other experimenters, particularly by Des- 

 pretz and Dulong. The French chemists assume as the unit of calorific 

 power, 1 gram of water heated 1° centigrade, (l.°8 Fahr.) Tho number of 

 such units produced by burning 1 gram of combustible is termed its colorific 

 efficiency. 



2. The melting of ice, as in the calorimeter of Lavoisier and Laplace, also em- 

 ployed by Hasseufratz. The heat of fluidity, (135° Fahr.) is here the mea- 

 sure of effect. 



3. The heating of air, or maintaining a certain difference between an interior 

 room in which combustion is conducted, and an exterior one, kept cool by the 

 open air. The length of time such difference is maintained by a given weight 

 of each fuel, is tho measure of its efficiency. This is the method of Mr. 

 Marcus Bull. 



4. Combustion in contact with metallic oxides, — measuring the heating 

 power by the weight of metal, reduced on the supposition that the latter is pro- 

 portionate to the weight of oxygen withdrawn. This is illustrated by M. 

 Berthier's process by litharge. 



5. The reduction of the nitrate or chlorate of potash to the stale of a carbo- 

 nate, by fusing these salts, and then gradually adding tho combustible, till com- 

 plete saturation has taken place. 



C. The practice of the Cornish engineers, of measuring the efficiency of fuel 

 by the weight of water, which a given bulk of it (as 1 bushel) will raise one 

 foot high, when burned under a boiler driving a pumping engine. 



7. The distillation of the coals to ascertain the weight of fixed carbon which 

 they contain, suggested by the experiments of Mr. Pfyfe, of Edinburgh ; the 

 weight of that constituent being supposed to measure the heating power. 



8. Ultimate analysis ,• which assumes that the quantity of heat developed 

 by an organic combustible, depends on the heating power of tho carbon which 

 it contains, added to that of its excess of hydrogen, above what is required to 

 combine with its oxygen in forming water. This method has been applied by 

 Messrs. Peterson and Schoedler to wood, and by Richardson, Regnault and 

 others, to coals. 



9. The director practical trial by evaporation, as practised by Messrs. Parkes, 

 Wickstced, Pfyfe, Schanfhautl and Manby in Great Britain, by Messrs. S. L. 

 Dana, A. A. Hayes, J. A. Francis, and more recently by Prof. J. himself in 

 this country. (The results of tho trials last referred to are contained in the 

 Report to the Navy Department on American coals recently published by 

 Congress ) 



10. The melting of iron either in a revcrberatory or a cupola furnace, the 

 weight of metal fused by one part of combustible boing the standard of com- 

 parison. 



