214 METALLOIDS. 



the hydrofluoric acid eats out the silicon of the glass, 

 where it is exposed, and passes off with it, in the form 

 of a new and more complex gas. A solution of the 

 gas may be prepared by the process employed for hy- 

 drochloric acid. Bottles of vulcanized India rubber, 

 or gutta purcha, may be used in keeping the solution. 



HYDROSULPHURIC ACID. 

 531. DESCRIPTION Hydrosulphuric acid 



What is hy- . 



dromlphuric is a colorless gas, also known as sulphu- 

 retted hydrogen. It has a putrid odor and 

 feeble acid properties. Like the rest of the series, it 

 is soluble in water. It occurs in many natural waters, 

 called sulphur springs. It is one of the products of 

 the decomposition of animal matter, and the source of 

 much of the disgusting odor which they emit during 

 putrefaction. 



Howisitpre- ^32. PREPARATION. It is made from 

 pared? sulphuret of iron, as hydrochloric acid 



is made from common salt ; and hydrofluoric acid 

 from fluor spar. In the above process, sulphuret 

 of iron furnishes the sulphur, and hydrated sul- 

 phuric acid, the hydrogen. The remaining elements 

 unite to form sulphate of iron, which remains in solu- 

 tion. On account of the disgusting smell of the gas, 

 it is best to prepare it only in small quantities. 



533. DISCOLORATION OF METALS AND 



What effect 



has it on met- PAINTS. The blackening of silver watches 



als, &c. ? an( j co i ngj i n t j ae v i c i n ity O f Sulphur 



