FLUORIC ACID. 499 



BORATE OF LIME. 



1. PROCESS. Mix boracic acid or borax with lime water, or any 

 soluble salt of lime. 



2. PROPERTIES. 



(a.) A white, insoluble, insipid powder ; fusible at ignition. 



(b.) Chalk 2, and boracic acid 1, at ignition, produce a yellow 

 glass so hard as to strike fire ; with the reverse proportions, the mat- 

 ter often runs through the crucible. 



BORATE OF MAGNESIA. 



1. PROCESS. By long digestion of boracic acid with magnesia; 

 or a mixture of any soluble borate with any soluble magnesian salt, 

 produces this combination. 



2. PROPERTIES. An insoluble and insipid precipitate, without 

 any crystalline form ; fusible, at ignition, into a white semi-transpa- 

 rent glass. 



The bi-borate of magnesia is found native at Luneberg, Germany, 

 under the name of the boracite ; it is in small cubical crystals, often 

 highly modified. 



BORATE OF ALUMINA. 



1. Newly precipitated and undried alumina is digested with bo- 

 racic acid. 



2. Evaporation gives a viscid mass, through which minute crystals 

 are interspersed ; taste astringent. 



SEC. VII. FLUORIC ACID. 



Remark. In order to entitle the fluoric acid to a place here, strict 

 method would require that a combustible basis should have been prov- 

 ed to exist in this acid, and that this base should be described in con- 

 nexion with the acid. But as we have no decisive proof as to the 

 nature of the fluoric radical, the present arrangement can be consid- 

 ered as provisional only ; for it remains yet to be seen whether fluo- 

 ric acid is composed of a combustible basis and oxygen, or of a 

 peculiar principle, analogous to iodine and chlorine, and hydrogen, 

 or whether it has a composition entirely peculiar ; for all analogy 

 leads to the opinion that it is compound. 



1. HISTORY. Re-discovered by Scheele, A. D. 1771 ;* for it ap- 

 pears to have been first obtained (A. D. 1670,) by the artist Shank- 

 hard, at Nuremburg; and also by Pauli, at Dresden, A. D. 1725, 

 who employed it, as Shankhard had done, to corrode glass, but 



Vide Scheele's Essays, Vol. I. 



