352 Analysis of Scientific Books and Memoirs. 



The next section treats of alloys. These Mr Dalton considers to be 

 chemical compounds. One striking instance of a true chemical compound 

 occurs in the alloy called • speculum metal. This alloy is formed out of 

 tin and copper. The smallest deviation from the true proportions, it is 

 well known, will spoil the alloy as a reflector. These proportions were, by 

 laborious experiment, ascertained by Mudge to be 32 of copper to 14^ of 

 tin. Now, dividing each of these quantities by 2, we get 16 of copper 

 = 4 atoms according to Dr Thomson, and 7.25 of tin = 1 atom. This, 

 be it observed, is the result of experiments made forty years ago, when 

 atomic weights had as yet been unheard of. 



To show that chemical investigations on the alloys are likely to afford 

 light on some points long known in practice, we shall quote, with a com- 

 ment of our own, Mr Dalton's table of the alloys of tin with lead. 



Weights. 



Tin. Lead. 

 .58 + 1 

 L16 + 1 

 1.73 + 1 

 2. 3 + 1 

 2. 9 + 1 

 3.47 + 1 



Fusing 

 I'oint. 



430° 



350 



340 



345 



350 



360 



The most fusible alloy, our readers will perceive, is that of 1 atom of 

 lead and 3 atoms of tin. Excluding the alloy of 1 atom of each metal, it 

 will be perceived, that the remaining five alloys taken successively, differ 

 in their smelting points only 10° or 5°. But the alloy of 1 atom of lead 

 with 1 atom of tin, differs in its melting point no less than 80° from that 

 of the alloy of 1 atom of lead with 2 atoms of tin. What, then, would be 

 the consequence, if a pot containing a mixture of these two alloys, both 

 perfectly liquid, should be cooled down to 400° .'' 430° being the melting 

 point of the alloy, 1 atom tin + 1 atom lead, we should expect that the 

 whole of this alloy in the pot should become solid ; and 350° being the 

 melting point of the alloy, 1 atom lead + 2 atoms tin, we should expect 

 that this alloy would remain liquid. Part would be solid, part liquid ; 

 and the mass should be in a sort of intermediate state, resembling that of 

 moist clay. Now the solder used by plumbers consists of a mixture of 

 the two alloys we are considering ; and it is well known that this solder 

 preserves a pasty-form long before it perfectly solidifies, so as to admit of 

 being moulded and pressed about a joint, somewhat like a lute. 



But though we agree with Mr Dalton in considering many alloys as 

 chemical compounds, we by no means would take for granted, that all al- 

 loys are compounds. Thus an alloy of silver and steel was formed by 

 Messrs Stodart and Faraday, by melting these two metals together. When 

 this alloy was forged into a bar, and then dissected by means of dilute sul- 

 phuric acid, the silver was discovered, not in combination with the steel, but 

 disseminated in threads throughout the mass. These threads of silver may 

 give toughness to the mass, just as hair imparts strength to common 

 mortar; but the silver is as distinctly in a state of mechanical mix- 



