Frederick Guthrie on Eutexia. 469 



one curvature, not more than five can touch, each touching all. 

 Chemical compounds are known containing more than five 

 elements. But this circumstance does not obliterate the limit 

 of the eutexia of alloys, which are neither atomic nor molecular. 



Salt Alloys. 



§ 207. It cannot be gainsaid that, vast as is the importance 

 in the arts of the elementary metals and their alloys, yet in 

 terrestrial nature the interaction and relationship of compound 

 bodies is at least of equal importance, and of far wider scope; 

 for the science of such interaction and relationship constitutes 

 the greater part of chemistry and petrology. 



Amongst the non-metallic elements we should expect the 

 class analogous with the eutectic alloys to be very restricted 

 in number, on account of the chemical attitude of such ele- 

 ments towards one another, that is their tendency towards 

 chemical union. 



Chemical compounds, however, all of which may for brevity's 

 sake be called salts, can give rise to an indefinite number of 

 eutectic bodies ; indeed to an indefinite number of series of 

 such bodies. The whole of the preceding memoirs on Salt-solu- 

 tions and Attached Water are in fact mainly a study of one such 

 series. The cryohydrates are nothing else than eutectic alloys 

 of the one salt called water with the various other salts. If 

 instead of fused ice (water) we employ another fused salt, say 

 fused table salt, we may expect to find it forming eutectic 

 alloys with other salts, whose characteristic should be fusi- 

 bility at a temperature lower than that of either (both) of its 

 constituents. 



§ 208. In choosing salts whose behaviour under such ex- 

 amination shall be as free as possible from ambiguity we 

 must avoid : — 



First, those which are decomposed when heated by them- 

 selves to anything like the temperature to which they are to 

 be exposed in the experiment. And we are safe in this respect, 

 if we confine ourselves to those which are not decomposed on 

 fusion. For the bodies we are seeking should have tempera- 

 tures of fusion below the temperature at which that one 

 of its constituents fuses whose temperature of fusion is the 

 lower of the two — it should be eutectic. 



Secondly, must be avoided those which react on one another 

 chemically, either in the sense of suffering double decomposi- 

 tion, or in that of direct combination whereby double salta 

 are formed. It will be shown in § 225-227 that it is not always 

 necessary to avoid the first of these contingencies. The possi- 

 bility of double decomposition is of course avoided when the 



