48 



SCIENCE 



[N. S. Vol. XXXI. No. 785 



temperatures it may be obtained with 

 seven molecules of crystal water. Now 

 would it then be right to conclude from 

 this that at room temperature the hydrate 

 in the solution is CuSO^.SHoO and at 

 lower temperatures CUSO4.7H2O? Obvi- 

 ously not, but we may say that it is at least 

 that indicated by the composition of the 

 compound that separates. In the solution 

 itself many additional water molecules 

 are combined with the salt molecules, and 

 the force of attraction gradually shades off 

 as the radius of the sphere of attraction 

 from the nucleus outward increases so that 

 it is quite impossible to ascribe any defi- 

 nite formula to the hydrate in the solution. 

 (I should like to add parenthetically here 

 that the recent attempts made to draw 

 conclusions as to how many water mole- 

 cules are attached to a portion of certain 

 •salts, from observations of changes of con- 

 centration that occur at the electrodes 

 ■during electrolysis, are also based upon 

 misapprehensions, but these details can 

 ■not be taken up here.) It is, moreover, well 

 known that when any physical property 

 ■of a solution is studied at different tem- 

 peratures the curve representing the al- 

 teration of that property with change of 

 temperature does not show sharp points of 

 inflection, indicating that whatever the in- 

 ternal alterations may be within the solu- 

 tion, they occur gradually rather than 

 suddenly. 



In the study of the various physical 

 properties of solutions with changing tem- 

 perature and changing concentration, it 

 has been absolutely demonstrated that dif- 

 ferent solutions behave quite differently, 

 and that solutions of compounds that are 

 chemically analogous show an analogous, 

 but by no means an identical, behavior. It 

 is consequently quite impossible to write 

 an equation that will hold for the various 

 known solutions— not even approximately. 



Attempts to formulate an equation for a 

 so-called perfect or ideal solution are about 

 as successful as an attempt to write an 

 equation for an ideal or perfect chemical 

 compound would be. In short, such equa- 

 tions are necessarily based upon postulates 

 that are not in accord with experimental 

 facts, and consequently the equations 

 themselves can not and do not agree with 

 what is actually observed. The attempts 

 to parallel solutions with gases in a quanti- 

 tative way would naturally suggest that 

 there might be an equation for an ideal or 

 perfect solution just as we are wont to 

 write an equation for a so-called ideal gas, 

 but the suggestion is quite misleading, just 

 as all of the efforts at a quantitative study 

 of solutions based upon gas analogies have 

 proved futile. This is true not only of 

 solutions of moderate concentration, but of 

 dilute solutions as well, as a careful un- 

 biased scrutiny of the numerous experi- 

 mental data that have been collected shows. 

 The act of solution is accompanied by all 

 of the phenomena that are observed in the 

 case of changes that are regarded as chem- 

 ical by common consent, and this shows that 

 solutions are chemical in character. We 

 commonly say that whenever substances 

 combine chemically with each other, the 

 new substance formed has properties that 

 are quite different from those possessed by 

 the original substances. While this is true, 

 it is also the case that some of the proper- 

 ties are not changed at all, while others are 

 but slightly modified, and still others are 

 very greatly altered indeed. So, for in- 

 stance, the weight remains unchanged dur- 

 ing chemical action; the specific heat is 

 frequently altered but little, whereas the 

 color, volume and other properties may be 

 very greatly affected. In general, we may 

 say that when an element or compound 

 enters into comhmation with other ele- 

 ments or compounds, each of the ingredi- 



