278 B?)zeUus's Experiments todctermiiiellie Compoailion [ArniL, 



Experiments on the Composition of Boracic Acid. 



With respect to this acid, we have direct experiments by 

 Davy, and by Gay-Lussac and Thenard. The former found 73 

 per cent, of oxygen, wliile the latter found only 33 per cent. As 

 it appeared to me very likely that the determination of the capa- 

 city of saturation of boracic acid would indicate which of these 

 two results, so different from each other, approached nearest the 

 truth, I undertook some experiments to determine that point. I 

 heated boracic acid to redness in a platinum crucible to drive off 

 the sulphuric acid with which it is usually contaminated. I 

 dissolved the I'used acid in boihng water, and crystallized it a 

 second time. The crystals being well dried were exposed on a 

 sand-bath to a heat alDOve 212°; but long before becoming red- 

 hot, they lost 0*221 of their weight. When heated in a platinum 

 crucible by means of a spirit lamp, the acid lost 0-129 more, 

 making the whole loss amount to 35 per cent. Ten graujuies of 

 crystallized boracic acid were mixed with 40 grammes of piu'e 

 oxide of lead and a quantity of water sufficient to dilute the 

 mixture. Tt was digested till the boracic acid had combined 

 with the oxide of lead. It vv^as then evaporated to dryness, and 

 exposed to a red heat. The calcined mass weighed 45"6 

 grammes ; therefore, 4*4 grammes of water had separated from 

 the crystallized acid by its union with the oxide of lead. This 

 is precisely twice as much as the acid had lost by the heat of a 

 sand-bath. The experiment appears then to prove that crystal- 

 lized boracic acid contains two portions of water; one of which 

 serves as a salifiable base ; while the other is the water of crys- 

 tallization. This last portion is disengaged by a lov/ heat, while 

 the other requires a higher temperature, or the addition of a base^ 

 to be separated entirely from the acid. The preceding experi- 

 ments lead to the supposition that the water which serves as a 

 base to the acid, separates at two different periods; one half 

 separates first, and the other remains united to the acid, in the 

 the form, to speak so, of a subborate of water. 



Ten grammes of crystallized borate of ammonia were mixed in 

 a retort with 40 grammes of pure lime. The retort was adapted 

 to a small tubulated receiver filled with caustic potash, and fur- 

 nished with a glass tube likewise filled with caustic potash, 

 through which the ammoniacal gas was to issue. The receiver 

 and tube with tiie j)otash were exactly weighed before the expe- 

 riment. The retort was then slowly heated, till at a lieat nearly 

 red, no more ammoniacal gas was disengaged. The apparatus 

 was then allowed to cool, the receiver was removed, and the 

 ammoniacal gas driven out of it by means of a current of air 

 "which passed over muriate of lime before entering into the 

 receiver. The receiver and tube had acquired 3*173 grammes 

 of water, and in tb.e retort, 3*795 granunes of boracic acid 

 remained united with the lime. The loss, amounting to 3-032 



