112 Frederick Guthrie on Salt- Solutions 



For the experimental examination of this curious question 

 the salt-alloy of nitrate of lead and nitrate of potash, described 

 in § 215, is excellently well adapted. Its composition is 

 46-86 nitrate of lead +53*14 nitrate of potash, and its fusing- 

 point, being 207°, is well within the range of the mercurial 

 thermometer. Its constituents at this temperature are far 

 below their temperature of decomposition, and, what is of 

 equal importance, both the nitrates are essentially anhydrous 

 at all temperatures above 0° C. 



§ 250. a grams of this salt-alloy, finely powdered and 

 freed from condensed moisture, were introduced into a 

 weighed tube. A little water being then introduced through a 

 capillary tube, the end was sealed off, and both re weighed, 

 the amount of water introduced being thus known. The sealed 

 tube was wrapped round in two places with copper wire, and 

 placed in a copper oil-bath. The bath was heated till com- 

 plete fusion was effected, the water and salt completely mixing 

 to a colourless limpid liquid. The wire enables the tube to be 

 taken out and the contents moved to and fro. 



When complete fusion is obtained the bath is allowed to 

 cool slowly, being kept well stirred. The temperature of inci- 

 pient solidification is observed several times, to avoid possible 

 errors arising from supersaturation, although with this salt- 

 alloy no such condition appears to obtain. As considerable 

 pressure may be exerted on the tube, it and the thermometer 

 were viewed through two sheets of glass six inches apart. 

 None of the tubes, however have burst. 



The following results were obtained: — 



Percentage of Solidifying 



Salt. temperature. 



100 207° 



99-82 203° or 204° 



98-24 197° 



§ 251. These results are striking and important. The 

 phenomenon of fusion per se is continuous with, and nothing 

 more than an extreme case of, liquefaction by solution. When 

 we are considering such a case as the second, near the top, 

 where 0*18 weight of water dissolve 99-82 of salt, we are in- 

 duced to regard it as a solution of water in the fused salt 

 rather than the converse, especially as the solidifying-point is 

 so near that of the dry salt. It will be readily granted that a 

 proportion of the alloy and water having even less water than 

 the above will have an incipient solidifying temperature even 

 closer to the temperature of fusion of the dry alloy. Hence 



