372 Dr. C. R. Alder Wright. [Jan. 28, 



This was found to be the case. The curve of the beam from scale 

 No. 46'3 of the spectrum (about X 5613) was found to be straight 

 from the origin. Those of beams of greater refrangibility were at 

 first concave to the axis of abscissae, those of less refrangibility 

 convex; but all had become straight before an intensity of 1/60 of an 

 amyl acetate lamp at 1 foot had been reached. 



III. " On certain Ternary Alloys. Part V. Determination of 

 various Critical Curves, and their Tie-lines and Limiting 

 Points." By C. R. ALDER WRIGHT, D.Sc., F.R.S., Lecturer 

 on Chemistry and Physics in St. Mary's Hospital Medical 

 School. Received November 19, 1891. 



The triangular method of graphical representation suggested by Sir 

 G. G. Stokes, and described in Part IV (< Roy. Soc. Proc.,' vol. 49, 

 p. 174), substantially amounts to the tracing out of a curve (" critical 

 curve ") which shall express the saturation of the solvent C with a 

 mixture in given variable proportions of the other two constituents, 

 A, B ; the variation being such that any given point on the curve 

 is related to some other point ("conjugate point") in a way given 

 by the consideration that all mixtures of the three constituents, 

 A, B, C, represented by points lying on the line ("tie-line") joining 

 these two conjugate points (" ideal " alloys, or mixtures), will separate 

 into two different ternary mixtures corresponding with the two points 

 respectively; whereas any mixture of the same constituents, repre- 

 sented by a point lying outside the critical curve, will form a " real " 

 alloy, or mixture, not separating spontaneously into two different 

 fluids but existing as a stable homogeneous whole. 



The experiments described in Part IV unmistakably point to the 

 conclusion that whenever sufficiently intimate and prolonged intermix- 

 ture of the three constituents can be effected, there is no variation what- 

 ever in the position of the point experimentally determined as 

 conjugate to some other given point on the curve, no matter what 

 may be the proportions subsisting between the three constituents 

 employed ; but that when metals are used, the practical difficulty in 

 effecting thorough intermixture by stirring when molten is occasion- 

 ally so great as to lead to slight, but sensible, differences in the 

 composition of the ternary alloys formed simultaneously with some 

 one given alloy approximately conjugate thereto, in different cases 

 where the relative proportions of the constituents are materially 

 different. 



A large number of additional experiments on this point have been 

 made, the general result of which is completely to corroborate and 



