176 THE ATOMIC WEIGHTS. 



ALUMINUM. 



The atomic weight of aluminum has been determined by Berzelius, 

 Mather, Tissier, Dumas, Isnard, Terrell, Mallet, and Baubigny. The 

 early calculations of Davy and of Thomson we may properly disregard. 



Berzelius' * determination rests upon a single experiment. He ignited 

 10 grammes of dry aluminum sulphate, A1 2 (S0 4 ) 3 , and obtained 2.9934 

 grammes of A1 2 3 as residue. 



Hence Al = 27.103. 



In 1835 1 Mather published a single analysis of aluminum chloride, 

 from which he sought to fix the atomic weight of the metal. 0.646 grm. 

 of A1CL, gave him 2.056 of AgCl and 0.2975 of A1 2 3 . These figures give 

 worthless values for Al, and are included here only for the sake of com- 

 pleteness. From the ratio between AgCl and A1C1 3 , Al = 28.584. 



Tissier's J determination, also resting on a single experiment, appeared 

 in 1858. Metallic aluminum, containing .135 per cent, of sodium, was 

 dissolved in hydrochloric acid. The solution was evaporated with nitric 

 acid to expel all chlorine, and the residue was strongly ignited until only 

 alumina remained. 1.935 grm. of Al gave 3.645 grm. of A1. 2 3 . If we 

 correct for the trace of sodium in the aluminum, we have Al = 26.930. 



Essentially the same method of determination was adopted by Isnard, 

 who, although not next in chronological order, may fittingly be men- 

 tioned here. He found that 9 grm. of aluminum gave 17 grm. of A1. 2 3 . 

 Hence Al = 26.8 



In 1858 Dumas, 1 1 in connection with his celebrated revision of the 

 atomic weights, made seven experiments with aluminum chloride. The 

 material was prepared in quantity, sublimed over iron filings, and finally 

 resublimed from metallic aluminum. Each sample used was collected 

 in a small glass tube, after sublimation from aluminum in a stream of 

 dry hydrogen, and hermetically enclosed. Having been weighed in the 

 tube, it was dissolved in water, and the quantity of silver necessary for 

 precipitating the chlorine was determined. Reducing to a common 

 standard, his weighings give the quantities of A1C1 3 stated in the third 

 column, as proportional to 100 parts of silver : 



*Poggend. Annal., 8, 177. 



tSilliman's Amer. Journ., 27, 241. 



J Cotnpt. Rend., 46, 1105. 



I Compt. Rend., 66, 508. 1868. 



|| Ann. China. Phys. (3), 55, 151. Ann. Cheni. Pharm., 113, 26. 



