158 



Proceedings of Learned Societies. 



as it relates to the element aluminium, is given. The subject was 

 introduced by a few words relating to the more ordinary aspects 

 under which this element is generally regarded. 



Of all the elements, aluminium is the third in order of abundance ; 

 among the metals themselves it is the most abundant. Yet it seems 

 not to be a necessary constituent of the animal or vegetable king- 

 doms ; in the mineral kingdom, however, it is widely distributed, 

 and occurs in immense quantity in rocks, and clays, and gems. It 

 has been turned to many useful purposes in the arts, as in the manu- 

 facture of pottery and porcelain, and in mordanting fabrics. In 

 spite of the abundance and the universal distribution of aluminium, 

 and notwithstanding its importance in the arts, the chemical con- 

 stitution of its compounds has received less attention than has been 

 accorded to the compounds of some of the rarer metals. 



The evidence as to the constitution of compounds, and the atomic 

 weight of elements is twofold : — 



b. 



Specific Heat. 

 Vapour Density. 



a. Specific Heat. We know that equal weights of different 

 elementary metals, heated to the boiling point of water, melt 

 different quantities of ice ; e. g., 1 part by weight of silver 

 melts twice as much ice as 1 part by weight of bismuth — 

 the specific heat of silver is, therefore, twice that of bismuth. 

 But, on the other hand, it is found that the atomic weights 

 of these two metals, taken, say in decagrammes, melt the same 

 quantity of ice ; therefore we conclude that atomic weights of 

 silver and bismuth have the same specific heat. Extending this 

 experiment to other elements, we find that the weights capable of 

 giving equal " melting power" will be f6r certain metals : — 



Lithium . 

 Magnesium 

 Zinc . . 

 Arsenic . 

 Silver 



Li = 1 

 Mg = 24 

 Zn = 65 

 As = 75 

 As = 108 



Tin . 



Mercury 

 Lead . 

 Bismuth , 



Sn = 118 



Hg = 200 

 Pb = 207 

 Bi = 210 



The foregoing numbers are, then, the atomic weights of the 

 above-named elements. 



Now the amount of aluminium having equal melting power to 

 108 of silver is 27S, not 9'2, nor 18-3, nor 367. The chloride is, 

 therefore, not Al' CI, nor Al" Cl 2 , nor AT"' Ch, but AT" Cl 3 . 



b. Vapour Density. The atomic weight of a metal will be the 

 quantity contained in two vols, of the gaseous chloride. Thus two 

 litres of hydrochloric acid, H CI = 1 crith* of hydrogen, H, + 35*5 

 criths of chlorine, CI : the atomic weight then of H = 1 . And so 



* Crith. The term crith has been lately introduced into chemical language. 

 A crith of hydrogen is the weight of one litre of that gas at the standard tempe- 

 rature and barometric pressure. One litre of chlorine contains consequently 35 - 5 

 criths, 35'5 being the atomic weight of that element, and so on with other gases. 



