Frederick Guthrie on Eutexia. 477 



Mixtures consisting of 20 per cent, nitre and 80 per cent, 

 nitrate of lead, and even 10 per cent, nitre and 90 per cent, 

 nitrate of lead, fuse together into clear liquids without decom- 

 position, but I have not determined the melting-points. At a 

 higher temperature the red peroxide of nitrogen is evolved, 

 but I do not know whether it is or is not accompanied by 

 oxygen. 



In the figure curve (1) shows the solidification-temperatures 

 of mixtures of nitrate of lead and fused ice (§ 152), and curve 

 (2) shows the solidification-temperatures of mixtures of nitrate 

 of lead and fused nitre. The abscissas are on the same scale 

 (1 millim. to 1 per cent, of lead salt). The ordinates are in 

 (2) 1 millim. to 1° C. ; in curve (1) 1 millim. to 0°'l. The 

 curve (2) is fetched down so that the two have a common 

 origin . 



§ 224. One of the widest generalizations with regard to 

 the behaviour of compound bodies towards one another is 

 that which assumes, in the case of two salts, that the bases are 

 shared in the first place by the acids, and that the result which 

 often ensues, that one base and one acid are ultimately found 

 in union to the exclusion of all others, is due to the succes- 

 sive withdrawal of such a combination when formed, either by 

 its insolubility or volatility. Accordingly we must not be 

 surprised that when the conditions of insolubility are varied, 

 the final selection may be wholly changed. The salt alloy 

 described in § 215, namely the eutectic alloy of nitre and 

 nitrate of lead, when mixed with the eutectic alloy of nitre 

 and sulphate of potash, § 216, and heated, forms a perfectly 

 transparent liquid. Sulphate of lead, which is so insoluble in 

 water, is soluble in fused nitre (see § 225) ; and a mixture may 

 be got identical with that got on heating nitrate of lead with 

 sulphate of potassium in the presence of nitrate of potassium. 

 There is in both cases equilibrium between the bases and acids. 

 When sulphate of lead is dissolved in fused nitre, it is to be 

 noticed that, at a considerably increased temperature, the red 

 oxide of nitrogen is given off, as when nitrate of lead is heated 

 by itself. Both nitre and sulphate of lead, when heated by 

 themselves, require a much higher temperature for their de- 

 composition ; this seems to show the existence of nitrate of 

 lead in the fused mixture. The liquidness of the fused alloy 

 does not show that no sulphate of lead is present : a certain 

 amount of lead is no doubt in union with sulphuric acid, but 

 is soluble in nitre as other salts are soluble in water. 



§ 225. Nitre and Sulphate of Lead. — On adding pure dry 

 sulphate of lead to fused nitre, solution ensues the more 

 abundantly the hotter the liquid. The amount of sulphate of 



Phil. Mag. S. 5. Vol. 17. No. 108. June 1884. 2 K 



