DETECTION OF ACIDS. 391 



37. DETECTION OF ACIDS. 



General remarks. There are no general methods (similar to those 

 for the separation of metals) by which all acids can be separated, first 

 into different groups, and afterward into the individual acids. It is, 

 moreover, impossible to render all acids soluble (when in combination 

 with certain metals) without decomposition, as, for instance, in the 

 case of carbonic acid when in combination with calcium ; calcium 

 carbonate is insoluble in water, and when the solution is attempted 

 by means of acids, decomposition takes place with liberation of carbon 

 dioxide. Many other acids suffer decomposition in a similar manner, 

 when attempts are made to render soluble the substances in which 

 they occur. 



It is due to these facts that a complete separation of all acids is 

 not so easily accomplished as the separation of metals. There is, 

 however, for each acid a sufficient number of characteristic tests by 

 which it may be recognized ; moreover, the preliminary examination, 

 as well as the solubility of the substance, and the nature of the metal 

 or metals present, will aid in pointing out the acid or acids which 

 are present. 



If, for instance, a solid substance be completely soluble in water, 

 and if the only metal found were iron, it would be unnecessary to 

 test for carbonic and phosphoric acids and hydrogen sulphide, because 

 the combinations of these with iron are insoluble in water ; there might, 

 however, be present sulphuric, hydrochloric, nitric, and many other 

 acids, which form soluble salts with iron. 



Detection of acids by means of the action of strong sulphuric 

 acid upon the dry substance. The action of sulphuric acid upon 

 a dry powdered substance often furnishes such characteristic indica- 



either the arsenic or lead group? How can mercuric sulphide be separated 

 from the sulphides of copper and bismuth? How does ammonium hydroxide 

 act on a solution containing bismuth and copper ? State the action of strong, 

 hot hydrochloric acid on the sulphides of arsenic and antimony. Suppose a 

 solution to contain salts of iron, aluminum, zinc, and manganese, by what 

 process could these four metals be separated and recognized ? How can barium, 

 calcium, and strontium be recognized when dissolved together ? By what tests 

 is magnesium recognized? State a method of separating potassium when mixed 

 with other metallic compounds. How are ammonium compounds recognized 

 when in solution with other metals ? 



