Salts. 149 



vescence ; the reason of the effervescence is plain, 

 as it is caused by the expulsion of the carbonic 

 acid in the form of gas. Acids also unite with 

 metals, lime, &c. 



Lastly, the mineral acids show a remarkable 

 degree of acrimony or corrosiveness when ap- 

 plied to animal substances. If taken internally, 

 in their strong state, they are poisons ; if exter- 

 nally applied, they give pain like burning, and 

 destroy the part; if diluted, they prevent fer- 

 mentation and putrefaction, are astringent, &c. 



Some of the vegetable acids are so mild that 

 they may be safely taken into the stomach. 



1 st, Sulphuric (formerly called vitriolic) acid 

 announces its origin by its name. It is a com- 

 bination of sulphur with oxygen, and is obtained 

 by burning sulphur in air, or with any substance 

 containing oxygen. In the great way a cham- 

 ber is prepared lined with lead, on which metal 

 the sulphuric acid does not act. The bottom 

 of the chamber is a large leaden cistern contain- 

 ing water. In this place sulphur is burned, 

 together with a quantity of common nitre, which 

 is necessary to supply the oxygen, the chamber 

 being closed from the external air to confine 

 the vapour. The sulphur and oxygen rise in 

 the form of sulphurous gas, which is absorbed by 

 the water, and when it is of sufficient strength 

 it is drawn off into large glass vessels. The 

 superfluous water is afterwards expelled by 

 placing these vessels in a sand-bath till the acid 



