264 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



temperatures — a circumstance which tended towards a slight elevation 

 of the apparent atomic weight of aluminum as calculated from the 

 weighings. Two sets of experiments were made with the alum; one 

 upon a sample air-dried for two hours at 21°-25°, the other upon mate- 

 rial dried for twenty-four hours at 19°-2C)°. These sets, marked A and 

 B, respectively, differ slightly, B being the less trustworthy of the two, 

 judged from a chemical standpoint. Mathematically, it is the better of 

 the two. Calcination was effected with a great variety of precautions, 

 concerning which the original memoir must be consulted. To Mallet's 

 weighings I append the percentages of ALOg deduced from them : 



Series A. 



8.2144 grm. of the alum gave .9258 grm. AljO,- 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. AlA- 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, 11.2834, ± .0011 



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

 Al = 27.153. 



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 portion?, 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 



