﻿332 Intelligence and Miscellaneous Articles. 



working with the same limits of temperature. But even here he 

 takes as his lower limit of temperature the usual temperature of 

 the exhaust in the actual steam-engines, and not the lowest tem- 

 perature possible, say, the average atmosphere temperature : and 

 iu the case of the condensing-engine he makes his standard de- 

 fective in another way by limiting the maximum volume of the 

 standard engiue's cylinder. 



Instead of speaking of pounds of coal per hour per indicated 

 horse-power, he prefers to speak of pounds of steam ; and the 

 manufacturer of our generation is rightly proud to have reduced 

 this from numbers greater than 30 lb. of steam per hour per indi- 

 cated horse-power to numbers less than 14. To those of us who 

 lament the waste of our fuel, it is more instructive to consider the 

 absolute efficiency of the steam-engine. It is only the very largest 

 and best of steam-engines which can be said, even by their con- 

 structors, to give, during an exceptionally well-stoked trial, one 

 actual horse-power for 1*6 lb. of coal per hour. This means that 

 the energy utilized is only about 17 or 18 per cent, of the supply 

 in the very largest and best of steam-engines ! There is some 

 comfort in the thought that even in small gas-engines 1 actual 

 horse-power is obtained from very little more than 1 lb. of 

 anthracite per hour when Dowson gas is used. In the animal 

 machine over 90 per cent, of the supply of energy in the fuel may 

 be converted into useful mechanical work. The man who first 

 shows us how, in a small space and without excessive cost of plant, 

 we can convert the chemical energy of coal and air into electrical 

 energy, as zinc is burned in a voltaic cell, will be the greatest 

 benefactor of his race — if he only comes soon enough. 



John Peeet. 



XXXYII. Intelligence and Miscellaneous Articles. 



HEAT OF DISSOCIATION ACCORDING TO THE ELECTROCHEMICAL 

 THEORY. BY H. EBERT. 



T^YERT stage in the development of chemistry can show experi- 

 -^ ments made to account for the forces which hold together the 

 atoms in compound bodies. In immediate connexion with 

 Kekule's doctrine of Valency, A T on Helmholtz, on the basis of 

 Faraday's law of Electrolysis, was the first to show in the case of 

 electrolytes, that each valency must be considered charged with a 

 minimum quantity of electricity, the " valency-charge," which like 

 an electrical atom is no longer divisible*, so that chemical affinities 



* That for electricity also there are minimal quantities which can be 

 no longer divided, and which are associated with the smallest particles 

 of ponderable masses, may be differently expressed. Let e be this 

 elementary quantity, and X, Y, and Z the components of the forces 

 exerted by it, then 



e=-l/4*r(dX/d*+dY ^y+^Z.^z). 



The expression within the brackets is, however, nothing more than the 



