Skction III., 1905 [ 67 ] Trans. R S. C. 



VIII. — The Yolliard Method for the Determination of Chlorine in 



Potahle Waters. 



By Feank T. Shutt, M.A., F.I.C., and H. W. Charlton, B.A.Sc. 



(Read May 24, 1005.) 



In judging of the purity of a water supply the chlorine content, 

 as is generally admitted, is a factor of the greatest importance. It is 

 of especial value when comparing waters from adjacent sources or those 

 collected at different points from the same source — as from a river or 

 lake. In such cases a difference of a few parts per million of chlorine 

 may be sufficient to establish sewage contamination. It becomes, 

 therefore, a matter of the greatest consequence that the water analyst 

 should be possessed of a process whereb}^ he can determine the chlorine 

 with accuracy. 



The process practically in universal use for the estimation of 

 chlorine in waters is that known as the " chromate " method — a de- 

 scription of which is to be found in all works on water analysis. In 

 the majority of cases this method is 'eminently satisfactory, but there 

 are some waters with which it fails to give a sufficiently close reading 

 for diagnostic purposes, and again others with which it is altogether 

 impossible to obtain a definite end re-action. We have, for instance, 

 found that the chromate method is extremely unsatisfactory, practically 

 valueless, for many "upland surface" waters, namely, those brown 

 from dissolved peaty matter and characterized by a low chlorine content. 



To learn if more satisfactory results could not be obtained, parti- 

 cularly with peat}' waters, we adapted some two months ago the Volhard 

 method and have since that time examined by it more than 60 samples 

 representative of all classes of potable waters. In this we have met 

 with gratifying success, for in no case has it been found to fail. Du- 

 plicate determinations agree very well, the end re-action being sharp 

 and easily noted. Indeed, it is safe to say that if the Volhard were as 

 rapid as the chromate method it would soon replace it. Our opinion 

 is, however, that its usefulness is rather as an auxilliary or supplement- 

 ary method than one to replace entirely the older process. 



The Volhard Method. 



Solutions. — The same silver nitrate solution is used as is employed 

 in the chromate method, viz., of such a strength that 1 c.c. = .001 

 chlorine. 



A solution of potassium sulpliocyanide, of such a strength that 

 1 c.c. corresponds to 1 c.c. of the silver nitrate solution. (Note, am- 

 monium sulphocyanide cannot be used). 



