276 A GENERAL FORMULA FOR THE 



It is obvious that the process I have described, adapted to 

 the most complicated composition which usually occurs, is to 

 be modified according to the ingredients. If no lime, for ex- 

 ample, is present, then the oxalate of ammonia is not employ- 

 ed ; and in like manner with regard to the others. I have al- 

 so supposed the usual and obvious precautions to be observed, 

 such as not adding an excess of any of the precipitants, bring- 

 ing the products to a uniform state of dryness, &c. having 

 mentioned only any source of error less obvious, or peculiar to 

 the process itself. 



With regard to other ingredients, either not saline, or more 

 rarely present, it will in general be preferable, when their pre- 

 sence has been indicated by the employment of tests, or by re- 

 sults occurring in the analysis itself, not to combine the inves- 

 tigation to discover them with the general process above de- 

 scribed, but to operate on separate portions of the water, and 

 to make the necessary allowance for their quantities in es- 

 timating the other ingredients. The quantity of iron, for ex- 

 ample, in a given portion of the water, may be found by the 

 most appropriate method. Silica will be discovered by the 

 gelatinous consistence it gives on evaporation, and forming a 

 residue insoluble in acids, but dissolved by a solution of pot- 

 ash. Alumina may be discovered in the preliminary application 

 of tests, by the water giving a precipitate with carbonate of am- 

 monia, which is not soluble, or is only partially soluble in weak 

 distilled vinegar, but is dissolved by boiling in a solution of 

 potash, or by its precipitation from the water sufficiently eva- 

 porated by succinate of soda; or in conducting the process it- 

 self, it will remain in solution after the precipitation of the 

 lime by the oxalic acid, and be detected by the turbid appear- 

 ance produced on the addition of the carbonate of ammonia 

 previous to the addition of the phosphoric acid to discover the 



magnesia. 



