SULPHURIC ACID. 165 



gold, the vessels in which the evaporation is carried 

 on, are extremely expensive. Some manufactories de- 

 liver tens of thousands of pounds of sulphuric acid per 

 day. 



397. COMPARATIVE STRENGTH OF SUL- 



Hov) is the 



strength of PHURIC ACID. SulphUHC acid JS the 



S shmvn? iC cid stron g est of a11 acids - This ma 7 be shown 

 by bringing it to a direct 'trial of strength 

 with other strong acids. If poured, for example, on 

 nitrate of potassa, which is, as its name implies, a com- 

 pound of nitric acid and potassa, it takes sole possession 

 of the base, and expels the nitric acid in the form of 

 vapor. It expels muriatic acid from its compounds in 

 the same manner. This is the method by which nitric 

 and muriatic acids are always obtained. Whatever 

 they can accomplish when free, may therefore be 

 traced back to the power of sulphuric acid, which gave 

 them their liberty. The latter is the king among the 

 acids, who accomplishes indirectly, what he cannot ef- 

 fect in person. The solution of the noble metals by 

 aqua regia is one among these indirect results. 



398. Sulphuric acid is volatile at high 



Is it strongest 



at high tenipe- temperatures. Phosphoric, and other non- 

 volatile acids, are, therefore, under certain 

 circumstances, superior to it. This is illustrated in cer- 

 tain crucible operations, where compounds containing 

 sulphuric acid are heated with such acids. The sul- 

 phuric acid is then easily dispossessed, and compelled 

 to take refuge in flight. 



What is the 399. ACTION OF SULPHURIC ACID ON 



action of sul- METALS . Sulphuric acid attacks all metals, 



jjliunc acid 



on metals. with the exception of platinum and gold. 



