ALUMINUM. 



161 



The closing series of experiments was made with larger 

 quantities of aluminum than were used in the foregoing- 

 set. The hydrogen, evolved by the action of the caustic 

 alkali, was dried by passing it through two drying tubes 

 containing j^umice stone and sulphuric acid, and two others 

 containing asbestos and phosphorus j)entoxide. Thence it 

 passed through a combustion tube containing copper oxide 

 heated to redness. A stream of dry nitrogen was employed 

 to sweep the last traces of hydrogen into the combustion 

 tube, and dry air was afterwards passed through the entire 

 apparatus to reoxidize the surface of reduced co];)per, and to 

 prevent the retention of occluded hydrogen. The water 

 formed by the oxidation of the hydrogen was collected in 

 three drying tubes. The results obtained were as follows. 

 The third column gives the amount of water formed from 

 10 grammes of aluminum : 



2.1704 grm. Al gave 2.1661 grm. HjO. 9.9S02 

 2.9355 " 2.9292 " 9.9785 



5.2632 " 5-2562 " 9.9867 



Hence Al = 2r3.998, ± .007, 



Mean, 9.9818, ± .0017 



In combining the various determinations of the atomic 

 weight of aluminum into one general mean, we must arbi- 

 trarily assign weight to the single experiments of Berzelius, 

 Isnard, Tissier, and Terrell. This may fairly be done by 

 giving to each the probable error, and therefore the weight, 

 of a single observation in Dumas' series. Mather's work 

 may be ignored altogether : 



From Berzelius Al = 27.243, ±.201 



11 



