[SHUTT & CHARLTON] VOLHARD METHOD OF CHLORINE 71 



In a large number of these examples the results by the chromate 

 method are sufficiently accurate for ordinary purposes, but the very fact 

 that among these waters there were 5, the chlorine of which could only 

 be satisfactorily determined by the Volhard process, emphasizes the 

 value of this latter method for water analysis. 



It is to be observed that the particular usefulness and accuracy of 

 this process is with waters containing very small amounts of chlorine 

 — a fact which enhances its importance for the examination of upland 

 surface waters which are naturally low in chlorides. 



In the Volhard method no check or blank is required, and hence 

 one source of error is avoided. In the chromate method the check may 

 require from .3 to .5 c.c. silver nitrate solution, according to the char- 

 acter of the distilled water. This means, if only 10 c.c. of the water 

 were under examination, a possible error of 30 parts per million. 



With the chromate method 100 c.c. of the water sample is com- 

 monly employed for the titration, smaller quantities being taken of 

 waters with high chlorides and made up to that volume. The Volhard 

 does not necessitate any fixed volume for titration and experience has 

 shown that the filtrate and washings may vary from 80 c.c. to 120 c.c. 

 without affecting in the least the results. 



Our custom now in the laboratories of the Experimental Farms is to 

 examine all the waters received for analysis by the chromate method; 

 if a satisfactory end re-action is obtained the results are accepted as 

 correct. If, however, difficulty is met with in this particular the Vol- 

 hard process is employed, and in no instance has the latter failed to 

 give a reading at once clear and decisive. 



