n THE ACIDS 15 



as SPIRIT OF SALT ; another common name for the acid is 

 MURIATIC ACID (Latin, murium, brine). The gas itself 

 was first isolated by Priestley, who showed that it could be 

 collected quite readily over mercury. 



Glauber also showed that the mixture of spirit of salt and 

 aqua fortis, which is produced by distilling salt and saltpetre 

 with oil of vitriol, was capable of dissolving gold and had 

 the same properties as the aqua regia prepared by Geber's 

 method. 



B. PROPERTIES OF THE ACIDS. 



Taste. Action on vegetable dyes. The most con- 

 J spicuous property possessed by all the above acids was their 

 sour taste. To this may be added the fact that they were 

 capable of changing the colour of various vegetable dyes. 

 During the eighteenth century, SYRUP OF VIOLETS, which 

 changes from violet to red on the addition of an acid, was 

 largely used as a test or INDICATOR for these substances ; at 

 a later date " tournesol," or LITMUS, which changes from 

 blue to red more easily than syrup of violets, and various 

 artificial dyes, were used for this purpose. 



When concentrated, the mineral acids were found to have 

 very corrosive properties. Glauber describes the charring of 

 a slip of wood and the ignition of turpentine and of spirit of 

 wine as properties of the strongest oil of vitriol. Aqua fortis 

 was equally corrosive, but both acids become harmless when 

 sufficiently diluted. The diluted mineral acids were at one 

 time employed in medicine and as substitutes for vinegar 

 and lemon-juice in the preparation of food. 



Action on alkalis and chalk. When added to soda or 

 potash all the acids were found to produce the violent effer- 

 vescence that was first noticed in the action of vinegar on 

 soda (p. 4). A similar " breaking out of air " took place 

 when chalky materials were acted on by acids : in this action 



