Bibliography. 167 
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 main- 
tained by a given weight of each fuel, is the measure of its efficiency. 
This is the method of Mr. Marcus Bull. 
4. Combustion in contact with metallic oxides, measuring the heat- 
ing power by the weight of metal, reduced on the supposition that the 
latter is proportionate.to the weight of oxygen withdrawn. This is illus- 
trated by M. Berthier’s process by litharge. 
5. The reduction of the nitrate or chlorate of potash to the state of a 
carbonate, by fusing these salts, and then gradually adding the combus- 
tible, till complete saturation has taken place. 
6. The practice of the Cornish engineers, of measuring the efficiency 
of fuel by the weight of water, which a given bulk of it (as one 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 car- 
bon 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 de- 
veloped by an organic combustible, depends on the heating power of 
the 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 direct or practical trial by evaporation, as practiced by 
Messrs. Parkes, Wicksteed, 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 the 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 reverberatory or a cupola furnace, 
the weight of metal fused by one part of combustible being the stan- 
dard of comparison. 
ll. 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. 
The object of the present communication is mainly to exhibit the 
relation between the results obtained by the eighth, and those by the 
ninth method of trial above mentioned. 
