NA TURE 



[May 5, 1904 



By drawing curves corresponding to various pressures, we 

 get therefore generally the diagram shown in Fig. 4, the loci 

 of the distinguishing- points forming one curve. Between 



the infinite possibilities of the shape of this curve we have 

 a distinguishing case again, the case that the curve is a 

 vertical straight line. This means that the composition is 

 independent of the pressure. When this is the 

 case, we call this hylotropic body a substance 

 or a chemical individual. 



Therefore we conclude that a connection 

 exists between solutions and chemical com- 

 pounds or substances, the latter being a dis- 

 tinguishing case of the former. On the other 

 hand, we get an e.xact definition : a substance 

 or a chemical individual is a body, which can 

 form hylotropic phases within a finite range 

 of temperature and pressure. 



Such substances can often be produced from 

 other substances in the same way as a solution 

 is, namely, by putting them together. If that 

 can be done, we may infer from our definition 

 that there exists a definite ratio between the 

 components, independent of temperature and 

 pressure between certain limits. 



Now, this is essentially the laiu of definite 

 proportions, the first of the stoichiometrical 

 laws. We have deduced, therefore, the la%v of 

 constant proportions from the concept of the 

 chemical individual. 



As you have seen, this deduction is extremely 

 simple; the constancy of composition is a 

 natural consequence of the mode of preparation 

 and purification of chemical substances. 



If we exceed the limits of temperature and 

 pressure, where the body behaves as a hylo- 

 tropic one, it assumes the properties of a solu- 

 tion, that is, its distinguishing point begins 

 shifting in composition when the temperature 

 is changed. Then it becomes possible to 

 separate the body into its components, and 

 we call this state the state of dissociation of 

 the substance in question. In our graphic 

 representation, the hitherto straight vertical 

 line of distinguishing points turns sideways. 

 Fig. 5. Most substances behave in this way, but there are 

 substances which have never been transformed into solutions 

 or the sphere of existence of which covers all accessible 



states of temperature and pressure. Such substances we 

 call elements. In other words, elements are substances 

 which never form other than hylotropic phases. 



From this we may conclude that every body 

 is finally transformable into elements, and into 

 only one definite set of elements. For the 

 most general case is a solution. Every solu- 

 tion can be separated into a finite number of 

 hylotropic components, and these again can 

 generally be transferred into a state when they 

 behave like solutions and can be separated 

 further. Finally, the components remain hylo- 

 tropic through the whole range of temperature 

 and pressure, that is, they are elenients. 



From the fact that the relation between a 

 compound substance and its elements admits of 

 only one qualitative and quantitative interpret- 

 ation, we derive the conclusion that the reso- 

 lution of any substance into its elements must 

 always lead to the same elements in the same 

 proportion. Here we find the source of the 

 law of the conservation of the elements. This 

 law is not generally expressed as a special 

 stoichiometrical law, because we tacitly infer 

 it from the atomic hypothesis. But it is truly 

 an empirical law, and we see that it is not only 

 a consequence of the atomic hypothesis, but 

 also a consequence of the experimental defini- 

 tion of an element and of our methods of 

 obtaining elements. 



Here I should like to pause for a moment 

 for the purpose of quoting a couple of historical 

 facts. Up to the present moment, the question 

 whether it is possible to deduce the stoichio- 

 metrical laws without the help of the atomic 

 hypothesis has only been raised by other 

 investigators in order to deny the possibility. 

 So far as I am aware, there exists only one man 

 who has worked upon the question with the earnest 

 hope of ol>taining an :tftirmati\e ^mswer. Wry few 



NO. 1 801, VOL 70] 



know his name. The man is Fran^ Wald ; he is 

 chief chemist at the iron works in Kladno, Bohemia. 

 His papers on the subject are to be found in the Zeitschrift 



