98 PKOCEEDINGS OF THE AMERICAN ACADEMY 



precisely with the equivalent numbers at that time in use, that I can- 

 not but think, considering the ditficulty of obtaining in a pure state 

 precipitates of a gelatinous consistency and decomposable by the cai'- 

 bonic acid of the air, that he has given the calculated numbers, and 

 not the results of his analyses. 



This subject was studied by me several years ago ; the results of 

 that investigation I have now the honor of laying before the Academy. 



On repeating Unverdorben's experiment, I found that neutral alumi- 

 nate of potash gives, as he states, a precipitate with chloi'ide of barium ; 

 much alumina, however, remained in solution, and on attempting to 

 wash the alurainate of baryta, the greater part of it dissolved and 

 passed through the filter. 



When freshly precipitated alumina is dissolved in hot concentrated 

 solution of baryta, a compound of these bodies separates in minute 

 crystals, which attach themselves to the sides of the vessel. If the 

 solution is dilute, it must be concentrated ; the crystals then form sud- 

 denly during the evaporation, and adhere so strongly to the glass that 

 it is difficult to remove them by mechanical means. They are trans- 

 parent, colorless, are hard and heavy, and, while covered by the liquid, 

 have an almost adamantine lustre. They are decomposed by the car- 

 bonic acid of the air, and by water, which separates from them 

 alumina. For these reasons, and from their adhesion to the glass, 

 it is somewhat difficult to collect them for analysis. 



1.0605 gr. of these crystals gave 0.972 sulphate of baryta and 0.2197 

 alumina ; whence we have for their composition. 



Found. Equivalents. 



1.96 

 1.00 

 5.32 



It is doubtful whether the salt contains 6 or 

 perhaps the more probable formula is 



2 BaO, AI2O3, 6 HO. 



In a preparation in which the baryta had been boiled with a con- 

 siderable excess of alumina, the liquid separated from the crystals 

 was evaporated in vacuo over sulphuric acid to dryness. There re- 

 mained an amorphous, friable, white mass, containing, exclusive of 



water, 



Ba 69.46 



AI2 O3 30.54 



