Frederick Guthrie on Eutexia. 467 



ice from a salt-solution. The residual liquid alloy should have 

 a composition analogous to that of a cryohydrate, and should 

 be the eutectic alloy of lead-silver. If this be so, its tempera- 

 ture of fusion should be lower than that of lead itself ; and 

 that it is so is proved by the separation of solid lead from the 

 melted mass. It is well known that Pattinson's process may 

 be "pushed too far." According to the above interpretation, 

 this simply means that when the fusion-temperature of the 

 eutectic alloy is reached, this body solidifies as a whole and is 

 raked away as the lead had been. A pyrometer, an air ther- 

 mometer, in the mass would be an absolutely trustworthy 

 guide as to the proper time for cupellation to replace " de- 

 leading." 



§ 205. That certain metals may and do unite with one 

 another in the small multiples of their combining weights may 

 be conceded. To such bodies the eutectic alloys bear the 

 same relationship as the cryohydrates bear to the common 

 hydrates, and, like the latter bodies, their constituents are not 

 in the ratio of any simple multiples of their chemical equiva- 

 lents. But their composition is not, on that account, the less 

 fixed, nor are their properties the less definite. Many of these 

 eutectic alloys have been known in partial purity for ages, 

 having been nearly reached by repeated trial or by assuming 

 a molecular ratio. But they have not been recognized as a 

 class numbering merely as dieutectics several hundred (say 

 1700), which can be obtained, as above shown, systematically 

 and in a state of great purity. Nor does the fact that several 

 instances are known in which metals combine with one another 

 in the chemical sense — that is, in simple multiple ratio by 

 weight of their combining weights and with liberation of heat 

 — at all diminish the possible number of such eutectic alloys. 

 For, firstly, as a salt may unite with water, as when anhydrous 

 chloride of calcium does so, to fix the water as crystalline 

 water, and also may unite with water as a cryohydrate, so two 

 metals may unite in one proportion while they form a definite 

 eutectic alloy in another. Secondly, the very bodies resulting 

 from the chemical union of the two metals will possibly, and 

 probably, furnish starting-points of new series of eutectic 

 alloys, consisting of a single metal on the one hand and the 

 chemical alloy on the other. 



§ 206. It will be instructive to compare the results given 

 above with results obtained by some previous experimenters 

 who have examined bismuth alloys. 



According to Rose, one part by weight of lead, one of tin, 

 and two of bismuth melt at 93°' 75. That a part of it may 

 melt, and so the whole soften at that temperature, need not be 



