Dr. Odlinor on Aluminium Ethide and Met hide. 317 



o 



The atomic proportions of the different metals unite with 1, 2, 3, 

 4, &c. atoms of chlorine and ethyle, to form the two-volume mole- 

 cules of their respective chlorides and ethides, as shown below : — 



2 vols. 



2 vols. 



2 vols. 



H CI 



H Et 





HgCl 2 



HgEt 2 



ZnEt 2 



Bi CI 3 



BiEt 3 



AsEt 3 



SnCl 4 



SnEt 4 



PbEt 4 



Or, two volumes of the gaseous chlorides of hydrogen, mercury, 

 bismuth, and tin, for instance, are found to contain respectively 35*5 

 parts, twice 35*5 parts, three times 35*5 parts, and four times 35*5 

 parts of chlorine. 



Aluminium, which is one of the three most abundant constituents 

 of the earth's crust, and the most abundant of all its metallic con- 

 stituents, enters into the composition of a large number of native 

 minerals of great value in the fine and useful arts, and also forms 

 extremely well-defined artificial compounds, possessing a high degree 

 of chemical interest. Nevertheless chemists are not at all agreed as 

 to the atomic weight which should be accorded to the metal, or as 

 to the molecular formula? of its principal compounds. 



The quantity of aluminium which has the same specific heat as 

 108 parts of silver, is found to be 27*5 parts ; and analysis shows that 

 this quantity of aluminium combines with three times 35'5 parts of 

 chlorine to form chloride of aluminium. Accordingly the atomic 

 proportion of aluminium should be fixed at 27*5 parts; its chloride 

 be formulated as a trichloride thus, A1C1 3 ; and its other compounds 

 be represented by corresponding expressions, as shown in the left- 

 hand column of the following Table, instead of by the heretofore- 

 used more complex expressions shown in the right-hand column : — 



Al 2/-5. Al 1375. 



A1C1 3 .... Chloride 



Na Al CI 4 .... Sodio-chloride 



Na 3 AlF 6 .... Cryolite 



Na 3 Al O 3 .... Aluminate 



H AlO 2 Diaspore 



K A1S 2 8 .. .. Alum] 



K AlSi 3 8 .... Felspar 



P AlO 4 .... Phosphate 



But the quantity of aluminium contained in two volumes of its 

 gaseous chloride was found by Deville to be 55 parts instead of 27*5 

 parts, while the quantity of chlorine was found to be six times 35 '5 

 parts instead of three times 35*5 parts. Hence, relying exclusively 

 upon molecular volume, the atomic weight of aluminium would be 

 55, and the formula of chloride of aluminium Al C1 B . This conclu- 

 sion, however, is inadmissible for several reasons, and chiefly because 

 it would make the atomic proportion of aluminium possess a specific 

 heat twice as great as that belonging to the atomic proportion of any 

 other metal. 



A1 2 C1 3 

 Na A1 2 C1 4 

 Na 3 Al 3 F 6 

 Na 3 Al 2 3 

 H A1 2 2 

 K A1 2 S 2 8 

 K Al 2 Si 3 O a 

 P A1 2 4 



