Qualitative Analysis

Qualitative Analysis is that branch of analytical chemistry which treats of the determination of the elements present in a chemical, but does not deal with the quantities. The methods employed are usually the application of a number of tests to a solution of the substance to be examined, the tests being applied in a regular order, so that some of the constituents of the compound are obtained in an insoluble form and so separated. As an example of the methods, if hydrochloric acid be added to a solution of silver, lead and mercurous salts and chlorides of these metals are precipitated. The precipitate is boiled with water, when the lead chloride is dissolved, and filtration leaves only the silver and mercurous salts. Adding ammonia effects the solution of the silver, and leaves the mercurous chloride as a blackened insoluble mass. By filtering again, therefore, the complete separation of the three salts is effected. The filtrate obtained from the hydrochloric is again treated in an analogous manner until all the metals present are determined. Other tests are applied for the acids. Tests in which flame colorations (q.v.) are used are also available, as well as numerous dry reactions in which the salts are heated mixed with suitable reagents. In the case of organic chemistry the qualitative analysis consists for the most part of a number of separate tests to deteraiine the presence of suspected elements.