159 



factory proof of their specific identity is that the offspring of 

 mixed blood is known to be both hardier and more prolific than 

 the more domestic variety, — a fact which cannot be reconciled with 

 the theory of specific difference. 



Dr. C. T. Jackson exhibited specimens of Aluminium 

 and several of its most important alloys with other 

 metals, and read a condensed resume of the various com- 

 munications on the subject contained in the Comptcs 

 Rendas of the French Academy of Sciences. 



The three most interesting alloys of aluminium are those with 

 silver, copper, and zinc. 



"When five per cent, of aluminium is added to pure silver it 

 increases the hardness of the metal and improves its quality for 

 plate, since this alloy is capable of receiving a high polish, and is 

 less liable to corrosion than the usual alloy of silver with copper. 



When ten per cent, of aluminium is fused with pure silver, a 

 much harder alloy results, which is still quite malleable and takes 

 a resplendent polish. This alloy also resists the action of sul- 

 phide of hydrogen which at once blackens pure silver and its 

 usual copper alloy. It is also well adapted, from its superior 

 hardness and stiffness, for the manufacture of forks and knives, 

 and plate made of it is less liable to be scratched and defaced by 

 use. 



The effects of aluminium on copper are quite remarkable, and 

 a very small proportion of aluminium is found to change the 

 color of copper to that of gold, while the alloy is much softer 

 and more ductile than pure copper. The whitening power of 

 aluminium when alloyed with copper, is much greater than thaT 

 possessed by zinc, and the alloys with aluminium are all malle- 

 able both when hot and cold. 



A specimen of an alloy of one hundred parts by weight of cop- 

 per and five parts by weight of aluminium was of the color of 

 British gold coin, and was readily rolled out into sheets thin as 

 letter paper, it working as easily as fine silver. 



It is stated in a communication published in the Gomptes Ren- 

 das, that this alloy is not affected by sulphide of ammonium ; but 

 tliis Dr. Jackson finds to be an error; for the moment a drop of 



