178 THE ATOMIC WEIGHTS. 



Series A. 



8.2144 grm. of the alum gave .9258 grm. A1 2 O 3 . 11.270 per cent. 



14.0378 " 1.5825 " 11.273 " 



5.6201 " '.6337 " 11.275 " 



11.2227 " 1.2657 " 11.278 " 



10.8435 " 1. 2216 " 11.266 " 



Mean, 11.2724, .0014 

 Series B. 



12.1023 grm. of the alum gave 1.3660 grm. A1 2 O 3 . 11.287 per cent. 



10.4544 " 1.1796 " 11.283 



6.7962 " .7670 " 11.286 " 



8.5601 " .9654 " 11.278 



4.8992 .5528 " 11.283 " 



Mean, n.,2834, .0011 



Combined, these series give a general mean of 11.2793, . 0008. Hence 

 Al === 26.952. 



The aluminum bromide used in the second series of experiments was 

 prepared by the direct action of bromine upon the metal. The product 

 was repeatedly distilled, the earlier portions of each distillate being re- 

 jected, until a constant boiling point of 263. 3 at 747 mm. pressure was 

 noted. The last distillation was effected in an atmosphere of pure nitro- 

 gen, in order to avoid the possible formation of oxide or oxy-bromide of 

 aluminum ; and the distillate was collected in three portions, which 

 proved to be sensibly identical. The individual samples of bromide 

 were collected in thin glass tubes, which were hermetically sealed after 

 nearly filling. For the titration pure silver was prepared, and after 

 fusion upon charcoal it was heated in a Sprengel vacuum in order to 

 eliminate occluded gases. This silver was dissolved in specially purified 

 nitric acid, the latter but very slightly in excess. The aluminum bro- 

 mide, weighed in the sealed tube, was dissolved in water, precautions be- 

 ing taken to avoid any loss by splashing or fuming which might result 

 from the violence of the action. To the solution thus obtained the silver 

 solution was added, the silver being something less than a decigramme 

 in deficiency. The remaining amount of silver needed to complete the 

 precipitation of the bromine was added from a burette, in the form of a 

 standard solution containing one milligramme of metal to each cubic 

 centimetre. The final results were as follows, the figures in the third 

 column representing the quantities of bromide proportional to 100 parts 

 of silver. Series A is from the first portion of the last distillate of AlBr 3 ; 

 series B from the second portion, and series C from the third portion : 



Series A. 



6.0024 grm. AlBr 3 = 7.2793 grm. Ag. 82.458 

 8.6492 10.4897 " 82.454 



3.1808' " 3.8573 " 82.462 



