212 METALLOIDS. 



assumes the gaseous form, and escapes with lively ef- 

 fervescence. An experiment may best be made with 

 zinc, to which a little dilute acid is added. 

 What is aqua 524. AQUA REGiA. On mixing muriatic 

 regia? ac {^ w ith half of its bulk of strong hydro- 



chloric acid, aqua regia is produced ; so called, from its 

 regal power over the noble metals. Gold and platinum, 

 which are not effected by either acid alone, dissolve 

 readily in aqua regia. The solvent power of aqua re- 

 gia depends, as before explained, on the nascent chlo- 

 rine which it supplies. 



525. HYDROBROMIC AND HYDRIODTC ACIDS. 



^lobromicand These acids are of interest to the chemist 

 hydriodie only. They resemble hydrochloric acid, 



acids ? . . 



in being colorless gases, strongly acid, 

 soluble in water, and capable of dissolving many 

 metals. 



HYDROFLUORIC ACID. 



526. DESCRIPTION. Hydrofluoric acid 



What is hy- 

 drofluoric is a colorless, corrosive gas, acting on glass, 



and many minerals which other acids do 

 not affect. It condenses into a liquid, at the freezing 

 point of water. It is not known to occur ready formed 

 in nature. 



527. PREPARATION. Hydrofluoric acid 



How is hydro- 



fluoric acid is made Irom a mineral called fluor spar, 

 prtpar by ttie game meai)S employed to make hy- 



dochloric acid. On account of its corrosive action on 

 glass, vessels of lead or platinum are employed in the 



