600 REPORT— 1897. 



able, and once for all determined ? Or are they constant merely so long as other 

 circumstances, a change in which would modify them, remain unchanged ? 



In order to understand the real scope of such questions, it is necessary to 

 consider the relation of the ' atomic weights ' to other magnitudes, and especially 

 to the important quantity termed ' energy.' 



It is known that energy manifests itself under different forms, and that one 

 form of energy is quantitatively convertible into another form, without loss. It is 

 also known that each form of energy is expressible as the product of two factors, 

 one of which has been termed the ' intensity factor,' and the other the ' capacity 

 factor.' Professor Ostwald, in the last edition of his ' Allgemeine Chemie,' classi- 

 fies some of these forms of energy as follows : 



Kinetic energy is the product of Mass into the square of velocity. 



Length into force. 

 Surface into surface tension. 

 Volume into pressure. 

 Heat-capacity (entropy) into temperature. 

 Electric quantity into potential. 

 ' Atomic weight ' into affinity. 



In each statement of factors, the ' capacity factor ' is placed first, and the 

 ' intensity-factor ' second. 



In considering the ' capacity factors,' it is noticeable that they may be divided 

 into two classes. The two first kinds of energj', kinetic and linear, are indepen- 

 dent of the 7iature of the material which is subject to the energy. A mass of lead 

 offers as much resistance to a given force, or, in other words, possesses as great 

 inertia as an equal mass of hydrogen. A mass of iridium, the densest solid, 

 counterbalances an equal mass of lithium, the lightest known solid. On the other 

 hand, surface energy deals with molecules, and not with masses. So does volume 

 energy. The volume energy of two grammes of hydrogen, contained in a vessel of 

 one litre capacity, is equal to that of thirty-two grammes of oxygen at the same 

 temperature, and contained in a vessel of equal size. Equal masses of tin and lead 

 have not equal capacity for heat ; but 119 grammes of tin has the same capacity as 

 207 grammes of lead, that is, equal atomic masses have the same heat capacity. 

 The quantity of electricity conveyed through an electrolyte under equal diflerence 

 of potential is proportional, not to the mass of the dissolved body, but to its 

 equivalent, that is, to some simple fraction of its atomic weight. And the capacity 

 factor of chemical energy is the atomic weight of the substance subjected to the 

 energy. We see, therefore, that while mass or inertia are important adjuncts of 

 kinetic and linear energies, all other kinds of energy are connected with atomic 

 weights, either directly or indirectly. 



Such considerations draw attention to the fact that quantity of matter (assum- 

 ing that there exists such a carrier of properties as we term ' matter ') need not 

 necessarily be measured by its inertia, or by gravitational attraction. In fact, the 

 word ' mass ' has two totally distinct significations. Because we adopt the con- 

 vention to measure quantity of matter by its mass, the word ' mass ' has come to 

 denote ' quantity of matter.' But it is open to anyone to measure a quantity of 

 matter by any other of its energy factors. I may, if I choose, state that those 

 quantities of matter which possess equal capacities for heat are equal ; or that 

 ' equal numbers of atoms ' represent equal quantities of matter. Indeed, we regard 

 the value of material as due rather to what it can do, than to its mass; and we 

 buy food, in the main, on an atomic, or perhaps, a molecular basis, according to 

 its content of albumen. And most articles depend for their value on the amount 

 of food required by the producer or the manufacturer. 



The various forms of energy may therefore be classified as those which can be 

 referred to an ' atomic ' factor, and those which possess a ' mass ' factor. The 

 former are in the majority. And the periodic law is the bridge between them ; 

 as yet, an imperfect connection. For the atomic factors, arranged in the order of 

 their masses, display only a partial regularity. It is vmdoubtedly one of the main 



