ON THE DETERMINATION OF CHLORINE IN NATURAL 

 WATERS, ITS ACCURACY AND SIGNIFICANCE. 



ERASTUS G. SMITH, PH. D., 

 Fio/essor of Chemistry , Beloit College. 



The detemiination of clilorine is one of the most familiar to 

 students of chemistry. The great accuracy possible in the manip- 

 ulations due to the practical insolubility of the chloride of silver, 

 the simplicity of the reactions, and the general principles illus- 

 trated recommend this determination to teachers of the science 

 as a first problem to set for the student coanmencing the study of 

 quantitative analytical chemistry. There are three methods for 

 estimating chlorine commonly used in the quantitative labora- 

 tory : 



1.) The gravimetric method, where the chlorine is precipi- 

 tated with silver and. weighed directly as the chloride. 

 2.) The volumetric methods : 



a.) With standard silver nitrate using potassiimi chromate 



as an indicator. (Mohr's method.) 

 b.} With silver nitrate and potassium thiocyanate using 

 ferric chloride as an indicator. (Volhard's method.) 

 All of these methods are in general use, the analyst exercising 

 his judgment as to which one to employ in any given case. 



In the analysis of natural waters, however, the conditions met 

 with in an ordinary analysis are materially changed. Chlorine, 

 whatever the combination, is in small amount; whatever method 

 therefore is used for its determination, it must be one where the 

 exactness of the results obtained is above question. In an ordi- 

 nary analysis of a chloride, e. g., a milligram error in weighing 

 up the material or the final precipitates would influence the 

 results in the calculations but slightly, so considerable are the 



