SG4 ^Y^scoJ^sin Academy of Sciences, Arts, and Letters. 



have showTi to be present; this is done because the color is de- 

 cidedly different when there is much precipitated silver chlor- 

 ide, thus masking the end-reaction, but if the chloride be added 

 to the comparison dish and the first change therein noted it will 

 materiallj assist in the final determination of the end-reaction 

 of the unknov^n water. 



There is little call for discussing the sanitary significance of 

 chlorine for it is well understood already. But what I want to 

 emphasize here is the fact that natural, perfectly wliolesome 

 waters always carry some small amounts of chlorine in some 

 form, generally as the sodium chloride. It makes little differ- 

 ence whence these chlorides come in a true unpolluted natural 

 water or whether they were at some period the product of the 

 animal economy as the natural processes of purification have 

 been at work and the accompanying undesirable matters have 

 been removed. All of this is within the field of research of 

 the sanitarian, and the healthfulness or the reverse of such 

 waters becomes a study for the biologist fully as much as for the 

 chemist. The character of sucli waters is all the more difficult 

 to pass upon because the chlorine is in such very small amounts 

 and the analytical difficulties increase with the diminution of 

 the amounts of dissolved matters. The exactness, therefore, of 

 the method becomes of great imj^ortance. It makes little dif- 

 ference with the interpretation of results from the sanitarian 

 standpoint whether a water carries 99 or 100 parts of chlorine 

 per million; but the difference between 1 and 1.1 partn may be 

 the difference between normal and polluted waters. 



Further, the exactness of the method also may well be scru- 

 tinized carefully in waters carrying so little chlorine where the 

 results of different analysts are to be compared. Does not the 

 personal equation in the observations of different analysts play 

 an important role here ? In w^hat other way can we reconcile 

 results we sometimes read given out by those in whom we have 

 the greatest confidence ? 



Before closing this brief paper I would like to call attention 

 to one of the needs of the state, viz. : the accurate determination 

 of the normals in chlorine for Wisconsin waters, as has been 

 done in some of the other states. The need for such normals is 

 apparent to those having to do with this kind of investigation. 



