244 Johnston and Adams — High Pressures on the 



of the reaction (potassium acetate) does. Here again the equi- 

 librium observed is that in the presence of water, and not that 

 of the pure dry solids. In fact if the pure dry powdered salts 

 are simply stirred together in the presence of water vapor, in 

 a very few moments deliquescence begins ; * so that the time 

 factor is here of very secondary importance, if indeed it exerts 

 any influence at all. This experiment again, therefore, offers 

 no proof that any chemical change took place before the water 

 vapor entered the system. 



C. The Reputed Formation of Alloys by Compression. 



By alternately compressing and filing down the compressed 

 block, Springf claims that he formed Wood's metal (from fil- 

 ings of bismuth, cadmium and tin in correct proportions), 

 Rose's alloy (from lead, bismuth and tin), and with greater 

 difficulty brass (from zinc and copper) ; his criteria for the 

 formation of the alloy were solely the general appearance and 

 the melting point of the specimens, neither of which can be 

 regarded in any way as conclusive evidence of the actual 

 formation of an appreciable quantity of the solid alloy. Simi- 

 lar experiments have been made by several later workers, none 

 of whom reach conclusions in entire agreement with those of 

 Spring. 



Thus the melting point criterion was shown to be useless by 

 Hallock4 He made a mixture of filings of cadmium (1 part), 

 tin (1 part), lead (2 parts), and bismuth (4 parts), and heated it 

 to about 98-100° ; in the course of a few hours a homogeneous 

 liquid globule of Wood's metal had formed. Similarly an 

 alloy formed on heating a piece of tin in contact with lead to 

 about 200° ; also when pieces of metallic potassium and sodium 

 were put in contact at the ordinary temperature, in which case 

 a thermoelement embedded in the potassium showed that the 

 temperature fell and remained below that of the surroundings 

 until reaction was complete. This behavior is exactly analo- 

 gous to that of the freezing mixtures ; for a salt and dry ice, 

 both at —10° or —12°, will combine rapidly. All of this 

 shows that an alloy may be formed from its constituents 

 by heating to a temperature above its melting point, though 

 far below the melting points of its constituents. 



This in itself does not directly settle the question at issue ; 

 but since that time all of those who have experimented along 



*Hallock, this Journal (3), xxxvii, 405, 1889; Bull. U. S. G. S., lxiv, 37, 

 1890. 



f Ber., xv, 595, 1882 ; Bull. soc. chim., xxxviii, 549, 1882. 



tU. S. Geol. Survey Bull. 60, 147, 1890; Bull. 64, 34-37, 1890; this 

 Journal (3), xxxvii, 402-6, 1889 ; Zs. phys. Chem., ii, 378-9, 1888. 



