64 Prof. L. Lorenz on the Determination of 



The relative unit of heat used here may be readily expressed 

 in absolute units of work ; defined in this measure we will ex- 

 press it by A. The unit of heat is equivalent to a work of 433 

 milligrammetres ; and as the weight of a milligramme is 9806 

 absolute units (that is, the acceleration of gravity expressed in 

 millimetres), we have 



A =425 x 10 7 absolute units. 



But to heat 1 mgrm. hydrogen at constant volume through 

 1° C, 



2'436A = 1035 x 10 7 absolute units are necessary. 



Just as a definite quantity of heat is necessary to raise the 

 same number of atoms of various elements through one degree, 

 so, according to Faraday's electrolytical law, equal quantities of 

 electricity are required to separate equivalent quantities from an 

 electrolyte. But as equivalent quantities do not always corre- 

 spond to the same number of atoms, it is necessary to choose a 

 definite type for electrolysis. 



As such a type I prefer the electrolysis of bodies constructed 

 on the formula RC1 (Br, S) — partly because an equal number of 

 atoms of the element are separated at each electrode, and partly 

 because we have here the greatest number of atoms which can 

 be separated from an electrolyte by the same quantity of electri- 

 city. All deviations from the type taken must then be regarded 

 as arising from secondary actions of the chemical forces. Thus, 

 while we regard the electrolysis of strong hydrochloric acid as 

 normal, the decomposition of water must be regarded as a de- 

 viation, which may perhaps be explained by assuming that two 

 atoms of oxygen unite to form a double atom. 



In the unit of time an electrical current of unit intensity 

 liberates in a voltameter -§\^ mgrm. hydrogen*. The same cur- 

 rent will liberate from strong hydrochloric acid the same weight 

 of hydrogen and as many atoms of chlorine — that is, will separate 

 at both electrodes as many atoms as are contained in ^q mgrm. 

 hydrogen. To raise the same number of atoms through 1° C. 

 under constant volume, we require, in accordance with what has 

 been said above, 



^^ A = 0-005075 A =216 x 10 5 absolute units. 

 480 



We may now define a degree of heat in absolute measure as 

 that increase of temperature which the unit of work produces, in 

 being completely and exclusively changed into heat, in the same 

 number of atoms of the element which the unit of electricity libe- 

 rates from an electrolyte under normal circumstances. 



* Conf. Wiedemann, Die Lehre vom Galvanismus, second part, p. 917. 



