BORACIC ACID. 311 



bines with sulphur, with the disengagement of light, when 

 heated in the vapour of that substance ; and it takes fire spon- 

 taneously in chlorine, and forms a gaseous chloride of boron, of 

 which the formula is BC1 3 , and the density 4035. This gas is 

 formed of 2 vols. of boron vapour and 6 of chlorine, condensed 

 into 3 vols. which are its combining measure. It may likewise 

 be formed, by transmitting chlorine gas over a mixture of bo- 

 racic acid and charcoal, ignited in a porcelain tube. A corres- 

 ponding fluoride of boron is evolved from boracic acid, ignited 

 with the fluoride of calcium or fluor spar, with the formation of 

 borate of lime. The density of this fluoride is 2308. 



Boracic acid. This acid is generally prepared by dissolving 

 the salt borax at 212 in four times its weight of water, the solu- 

 tion is filtered hot, and a quantity of oil of vitriol immediately 

 added to it, equal to one fourth of the weight of the borax. The 

 sulphuric acid unites with the soda, and forms sulphate of soda, 

 which continues in solution, while the boracic acid separates in 

 thin shining crystalline plates, on cooling. These plates are 

 drained, and being sparingly soluble, may be washed with cold 

 water, and afterwards redissolved in boiling water and made 

 to crystallize anew. The boracic acid still retains a small quan- 

 tity of sulphuric acid, probably in a state of chemical combina- 

 tion, and if required of absolute purity must be fused at a red 

 heat in a platinum crucible, then dissolved again and crystallized. 

 The density of the vitrified acid is 1.83. Boracic acid has a 

 weak taste, which is scarcely acid, and affects blue litmus like car- 

 bonic acid, imparting to it a wine-red tint, and not that clear red, 

 free from purple, which the stronger acids produce. It renders 

 yellow turmeric paper, brown, like the alkalies. The crystals 

 are a hydrate, and contain 3 equivalents of water, of which the 

 formula is HO, BO 3 + 2HO. At 60 it requires 25.66 times its 

 weight of water to dissolve it, but only 2.97 times at 212. 

 With the assistance of the vapour of water, it is said to be 

 slightly volatile, but alone it is fixed, and fuses, under a red 

 heat, into a transparent glass. The hydrated acid dissolves in 

 alcohol, and the solution burns with a fine green flame. At 

 the temperature of the air, boracic acid is relatively a feeble 

 acid, but at a red heat it displaces the greater number of those 

 acids which are more volatile than itself. It communicates 

 fusibility to many substances in uniting with them, and generally 

 forms a glass. On this account borax is much used as a flux. 



