ELISHA MITCHELL SCIENTIFIC JOURNAL 45 



will be left on the filter the red salt KClCuCl 2 . If the solution 

 is cooled to a slightly lower temperature before filtering-, the 

 crystals will be a mixture of the red salt and a screen salt 

 CuCl 2 .2KC1.2H 2 G. If the filtration had taken place at a still 

 lower temperature, the precipitate would have been the green 

 salt alone. That is confusing enough but it is not all. If' 

 the red salt is washed with water, the green salt is formed 

 while cupric chloride will go into solution. If the green salt 

 is washed with water, a white salt, KC1, is left behind. This 

 is bad enough when the three salts are colored differently; 

 but it is nothing to the difficulties that would beset a man if 

 the salts were all colorless, had the same properties, and could 

 be distinguished chiefly by their unknown atomic weights. 

 This is not mere fancy. I could cite an instance in which 

 two distinguished chemists analyzed what was in all proba- 

 bility a mixture of two salts, believing it to be homogeneous. 

 They were thus led to assume the existence of two new ele- 

 ments, the presence of which could not be shown in any other 

 way. 



The whole question of alloys has been put on a rational 

 basis by means of the phase rule. Roozeboom has outlined 

 the methods for studying iron and steel; Heycock and Neville 

 have cleared up the question of the bronzes. We can now 

 distinguish in a way that we never could have done before 

 between states of hysteresis and states of equilibrium. When 

 we eliminate hysteresis, the densities of alloys van- with the 

 composition just as they should. It seems not unreasonable 

 to hope that the tensile strength and other engineering prop-^ 

 erties of annealed alloys will also vary regularly with the per- 

 centage composition. The experience we have gained with 

 salt solutions and with fused alloys will stand us in good 

 stead when we come to consider fused magmas. I feel cer- 

 tain that many of the problems of geology can be solved only 

 by an intelligent application of the phase rule. Recently 

 some people have tried to make certain minerals synthetically 

 by fusing together the components in the proportions in 



