78 Dr. TnOMSON on the Melting Points of Alloys of Lead, ^c. 



tliese alloys. The object which ho had in view was to determine the 

 latent heat of melted lead and tin; and ho accomplished this by 

 measuring the length of time that the melted metal took to cool a 

 certain number of degrees. Hence the inaccuracy of his thermometer 

 did not affect the result of his experiments. I shall notice Kupfer's 

 experiments at the end of this paper. 



I may liere notice a curious mistake into which Rudbcrg has fallen. 

 He says that Dr. Black reckoned the latent heat of tin 500°, and that 

 of wax 175°. These latent heats were determined, not by Dr.'Black, 

 but by Dr. Irvine, while professor of chemistry in the College of Glas- 

 gow. Rudberg has mistaken the meaning of Irvine's conclusion. 

 When he says that the latent heat of tin is 500°, he does not mean 

 the number of degrees that tlio same weight of water would be raised ; 

 but the increase of temperature which the latent heat of tin would 

 produce in the tin if it were to be thrown into the solid metal without 

 melting it. The heat which would raise tin 500° would only raiso 

 water 33°. Hence the latent heat of tin, as referred to water, accord- 

 ing to Dr. Irvine's experiments, is 33°, while by Rudberg it is 25°. 

 The difference is not nearly so great as Rudberg supposed. It is 

 probable, from the care taken by Rudberg in his experiments, that his 

 determination is nearest the truth. 



I find that, when lead and tin are alloyed together, in all the pro- 

 portions tried, the alloy expands, or is more bulky than the two metals 

 when separate. Hence the specific gravity of the alloys is less than 

 the mean. The specific gravities and atomic weights of the metals I 

 used were — 



Specific Gravity. Atomic Weight. Kupfer. 



All of these alloys are malleable, and they all have a specific gravity 

 below the mean. Hence tin and lead expand in the act of uniting, 

 and occupy a greater volume tlian when separate. The following table 

 shows the specific gravity of these four alloys : — 



