52 



SCIENCE. 



[N. S. Vol. XXI. No. 524. 



heat of dilution is marked, we combine all 

 of what has stood the test with what is 

 good in Kahlenberg's conceptions and I 

 believe that we are nearly ready to take a 

 long step forward. One point must be kept 

 in mind, however. Raoult's experiments 

 preceded his formula. Before we can 

 hope to work out a satisfactory theory of 

 concentrated solutions, we must have ac- 

 curate measurements on concentrated solu- 

 tions and at present we have practically 

 none. "We need experiments at constant 

 temperature on the compositions of co- 

 existent liquid and vapor phases for binary 

 .systems with one volatile component and 

 with two volatile components. These 

 measurements are not easy to make and 

 that is one reason why they have not been 

 made. We have measured boiling-points 

 and freezing-points because they are easy 

 to measure ; but for a theory of concen- 

 trated solutions the value of such measure- 

 ments is very small. This is because 

 we are then measuring the combined effect 

 of the change of the pressure with con- 

 centration and with temperature, whereas 

 we ought to study the two separately. Fur- 

 ther, if we are to express our results in 

 volume concentrations we must give the 

 volume concentrations of both components. 

 It would be absurd to pass from dilute to 

 syrupy solutions of sugar, for instance, and 

 to treat the concentration of the water as 

 constant. Personally, I believe that the 

 theory of concentrated solutions is rela- 

 tively simple and that the difficulties have 

 been chiefly of our own making. My own 

 experience with ternary mixtures confirms 

 me in this view. In developing a theory 

 of concentrated solutions we must also keep 

 in mind the actual properties of the com- 

 ponents, a thing which we have not done 

 in the past. Thus the dissociation equa- 

 tion for liquid chloral hydrate can not be 

 the same as that for liquid chloral aleohol- 

 at(^ because chloral is miscible in all pro- 



portions with alcohol and forms two liquid 

 layers with water. This is a perfectly 

 obvious fact, yet no reference to it is to 

 be found in any text-book on physical 

 chemistry. 



In the last ten years the work of Rooze- 

 boom and others has brought the phase 

 rule to the front as a basis of classification 

 and as an instrument of research. The im- 

 portance of the phase rule is going to in- 

 crease very rapidly in the next decade. 

 The study of alloys has really only just 

 begun. Our knowledge of the carbon 

 steels is still very incomplete and unsatis- 

 factory. In fact, we know the constitution 

 only of a very limited number of binary 

 alloys. Nothing systematic is yet known 

 about the chemical properties of alloys 

 or about the conditions for electrolytic 

 precipitatioji. The variation of the engi- 

 neering properties, such as tensile strength, 

 torsional resistance, ductility, etc., with 

 varying concentration and varying heat 

 treatment is a subject Avhich can only be 

 worked out satisfactorily with the phase 

 rule as a guide. On the basis of what has 

 been done it appears quite safe to predict 

 that we do not yet know one half the pos- 

 sibilities of our structural metals. 



Quite recently the constitution of Port- 

 land cement has been established and we 

 owe this result to an application of the 

 phase rule. It will not be long now before 

 we get much clearer ideas on the causes of 

 the strength of cements and of the plas- 

 ticity of the clays. The time will soon 

 come in our engineering schools when the 

 subject known as 'Materials of Engineer- 

 ing' will have to be taught by the chemist 

 rather than by the engineer. 



The applications of the phase rule to 

 petrography will be numerous and will 

 come soon. It is evident that no rational 

 classification of minerals can be possible 

 until the constitution of the minerals has 

 been determined. The situation in regard 



