198 



CHEMISTRY. 



tion, especially malleability, ductility, fusibility, density or 

 specific gravity, and tenacity. 



271. Density. Most of the metals are dense, and there- 

 fore heavy substances. The idea of most people is that a 

 metal is of course heavy, and this was the idea also of phi- 

 losophers until Sir Humphrey Davy, in 1807, made his dis- 

 covery that potash and soda are oxides of metals. This is 

 illustrated in an anecdote of Dr. Wollaston, a celebrated 

 English chemist. Davy, just after he had succeeded in ob- 

 taining by a chemical process the metal potassium, of which 

 potash is the oxide, put a bit of it into the hands of Dr. 

 Wollaston, who spoke of it as being quite heavy, and was 

 surprised to learn that it was lighter than water. There is 

 a wide range in the specific gravities of the metals, as may 

 be seen from the following table, which contains a portion 

 of them : 



SPECIFIC GRAVITIES OP METALS. 



Sp. Gr. at 

 15.5 C. 



Platinum 21.50 



Gold 19.50 



Uranium 18.40 



Mercury 13.59 



Thallium 11.90 



Palladium 11.80 



Lead 11.45 



Silver 10.50 



Bismuth 9.90 



Copper 8.96 



Nickel 8.80 



Cadmium 8.70 



Cobalt 8.54 



Sp. Gr. at 

 15.5 C. 



Manganese 8.00 



Iron 7.79 



Tin 7.29 



Zinc 7.10 



Antimony 6.80 



Arsenic 5. 88 



Aluminium 2.67 



Magnesium 1.75 



Calcium 1.58 



Rubidium 1.52 



Sodium 972 



Potassium 865 



Lithium.. 593 



The comparison in this table is made with water, that being 

 considered 1. There is, you observe, a gradual diminution 

 in specific gravity in the list till we come to the last seven. 

 These are very light, three of them are even lighter than 



