258 Intelligence and Miscellaneous Articles. 



Boracic acid cannot be estimated in the state of aqueous solution, 

 by a method similar to that employed for arsenic and phosphoric 

 acids ; that is to say, by adding to the solution a weighed quantity 

 of oxide of lead recently calcined, evaporating the whole, and heating 

 the dried mass to redness. In fact, it is not possible to prevent the 

 volatilization of the Loracic acid by adding oxide of lead. The same 

 happens when a solution of nitrate of lead is added instead of the 

 oxide. 



Even when a weighed quantity of tribasic phosphate of soda (3NaO 

 PO") is added, no quantitative result is obtained ; for this salt does 

 not possess the property of preventing the volatilization of boracic 

 acid from its aqueous solutions. 



A quantitative estimate of this acid in aqueous solutions can be 

 obtained only by the addition of a known quantity of a fixed alka- 

 line carl)onate ; but this method is not convenient, occupies much 

 time, and requires besides the most rigorous precision. Carbonate 

 of soda is preferred to carbonate of potash, because the former is 

 more readily weighed with exactness. It is to be weighed after 

 fusion, and about an equal or twice the weight of the boracic acid 

 supposed to exist in the solution is to be employed ; it is to be dis- 

 solved in the solution, and the whole is to be evaporated by a gentle 

 heat. In the cold, carbonic acid is not extricated from alkaline car- 

 bonates by boracic acid ; and when heated, so as to evaporate, the 

 carbonic acid is expelled only in a very slight degree. It is only 

 when the whole has been evaporated to dryness, and the dry mass 

 begins to be heated and calcined, that the disengagement of carbonic 

 acid takes place ; it is then that the operation must be conducted 

 with the most precaution. At an intense heat the mass is very fluid ; 

 it is soft when the heat is low. If the fusion be effected in a small 

 platina crucible with the heat yielded by a spirit-lamp with a double 

 current of air, the product obtained does not alter in weight when 

 long kept. But it is a remarkable circumstance, that, if the crucible 

 be only moderately heated, the weight increases a httle, and it is not 

 possible again to obtain a constant weight. The result, however, is 

 the same whether the fusion of the mass be continued for a longer 

 or a shorter time, and consequently whether a stronger or gentler 

 heat be employed. 



The quantity of boracic acid contained in the fused mass is thus 

 determined : deduct from its weight that of the soda contained in 

 the carbonate employed, and also that of the carbonic acid disen- 

 gaged during the experiment; the proportion of boracic acid will 

 thus be obtained with precision. 



When carbonate of potash is employed, similar phaenomena occur ; 

 but the results obtained are rather less precise, for this carbonate in 

 its anhydrous state cannot be weighed with the same accuracy as 

 the carbonate of soda. 



The method al)ove described for ascertaining the quantity of boracic 

 acid in solution is but rarely applicable in practice, and only when 

 the solutions contain no other matter. 



