9 2 



SCIENCE PROGRESS. 



B will separate together as solids, or very probably as a 

 solid solution, and the body will remain at a very constant 

 temperature until it is completely solidified. Figure 4 gives 



F/G.4- 



Time. 



a diagrammatic representation of these stages in the cooling, 

 temperatures being measured vertically and times horizon- 

 tally from left to right. Whenever there is a decrease in 

 the rate of cooling due to the separation of solid matter, we 

 shall see in the cooling curve an angle as at M, or if an 

 isothermal transformation is taking place as at N and P 

 there will be a flat. 



It is obvious that in an alloy containing but little B, the 

 point M will be well marked because a large amount of A 

 can solidify before the concentration, and therefore the 

 freezing- point alters perceptibly ; in fact in very dilute 

 solutions there may be a flat at M. With a stronger solu- 

 tion of B the point M is harder to detect and may be 

 missed altogether. The length of the two flats at N and 

 P will depend on the proportions and on the solubilities of 

 the two metals. The temperature M will depend on the 

 amount of B present. The temperature at P, in the eutectic 

 state, is quite independent of the original proportions of the 

 two metals, and, in the case of one or two pairs of metals 

 known to the writer, this is true for the transformation 

 which begins at N. But it must be confessed that, in most 



