1821.] Atomic Weight of various Metals and Acids. 131 



VI. Boracic Acid. 



My experiments to determine the weight of this acid have 

 been attended with more difficulties than those on any other 

 substance to which I have hitherto turned my attention ; and 

 after all my attempts to obtain accurate results, I have been 

 obliged to rest satisfied with approximations, which, however, 

 contract the limits of uncertainty within a narrow compass. 



1. From Berzelius's experiments on borate of ammonia, it 

 follows that it is composed of 



Boracic acid 3,7*95 



Ammonia 30-32 



Water 31-73 



Toooo* 



Now this is equivalent to 



Acid 2-659 



Ammonia 2-125 



Water 2-223 



Now 2-125 is the weight of an atom of ammonia, and 2*223 

 approaches very nearly to 2*25, the weight of two atoms of 

 water. There can be no doubt that borate of ammonia is a 

 compound of one atom acid, one atom base, and two atoms 

 water. Hence it follows that 2*659 approaches very nearly to 

 the weight of an atom of boracic acid. 



2. I put into a platinum crucible 100 grs. of dry boracic acid, 

 obtained by decomposing borax by means of sulphuric acid, 

 washing the precipitate well with distilled water, and drying it 

 ou a filter. The crucible was covered with a lid, and exposed 

 for an hour to a strong red heat. The acid was fused into a glass 

 which weighed 53*6 grains. Besides this, the cover of the cru- 

 cible was coated with a varnish of boracic acid which weighed 

 1*9 gr. From this experiment we learn that the hydrate of 

 boracic acid is composed of 



Acid 55*5 or 2*806 



Water 44*5 2*25 



100-0 



It would appear, therefore, that the hydrate of boracic acid is 

 a compound of one atom acid + two atoms water. We see 

 that the weight of an atom of acid deduced from this experi- 

 ment (which I have repeated several times) is 2-806. 



Now the mean weight of the atom of acid deduced from the 

 analysis of borate of ammonia by Berzelius and my own analysis 

 of hydrate of boracic acid is 2-7325. This quantity differs sa 



* Annals of Pftllosophy (First Series), iii. 57. 



k2 



