Frederick Guthrie on Eutexia. 



475 



the alloy in § 219 to be a single salt, and find the eutectic 

 alloy between this and nitrate of lead. The lowest melting- 

 point is found to be 186° ; and the composition of the alloy, 

 derived from the result that 2*0280 grams gave 1*1613 gram 

 sulphate of lead or 1*2690 gram nitrate of lead, is as follows : — 



Per cent. Melting-point. 

 f Xitrate of potassium . . 38'02| 

 I Nitrate of sodium . . 1864 V 186°. 



Nitrate of lead . . . 43*34 j 



This of course implies that the above is the eutectic alloy of 

 these three salts. The eutexia of salt alloys of more than two 

 salts is a x^ry wide question upon which I can only here touch. 

 § 223. The following experiment completes the analogy 

 pointed out in § 218. Mixtures of nitre and nitrate of lead, 

 both in the form of powder, were made in different ratios from 

 95 nitre and 5 of nitrate of lead, 90 of nitre and 10 of nitrate 

 of lead, and so on ; these were put into test-tubes and heated 

 in an oil-bath, which was kept continually stirred. The mix- 

 ture was completely melted, and the temperature at which 

 solidification began was observed. The observations, being 

 repeated many times, gave the following results :— 



Temperatures at which solidification begins in melted 

 alloys of nitre with nitrate of lead of various strengths. 



Table XLIV. 







Temperature 





Nitre 



Nitrate of 



of beginning 



Nature of body 



per cent. 



lead per cent. 



of solidifica- 

 tion. 



separating. 



100 







320° 



Nitre. 



90 



10 



300 



M 



80 



20 



285 



)j 



70 



30 



268 



>> 



60 



40 



240 





5314 



46-86 



207 



Eutectic alloy. 



50 



50 



210 



Nitrate of lead. 



40 



00 



238 



M 



30 



70 



335 r?) 



J7 



It is of course necessary to heat the mixed powders, in each 

 B, beyond the temperature which proves to be the initial 



solidifying point of the mixed mass. On heating the column 

 of powder it is noticed first to shrink and cake together to 

 about a quarter of its former volume, reminding one of the 

 haking of clays. Indeed all phenomena of so-called incipient 

 fusion of compound bodies (the pasty state) may be due to 

 what takes place here, namely the formation of an eutectic alloy. 

 The decomposition of both terms of this alloy, at tempera- 



