908 



SCIENCE. 



[N. S. Vol. XII. No. 311. 



For measuring the amount of dissolved 

 coloring matter in waters, the platinum- 

 cobalt scale appears to be very generally 

 used, although the Nessler and natural 

 water standards and other methods are be- 

 ing used in important work. While the 

 platinum standard does not appear to be 

 wholly satisfactory, especially for very dark- 

 colored waters, it appears to be generally 

 suitable for ordinary use and serves well as 

 a basis of comparison for all results. Your 

 committee recommends that whenever any 

 other method is used for color measure- 

 ment, the relation of this method to the 

 platinum standard shall be indicated. In 

 the case of waters which are appreciably 

 turbid, the suspended matters should be 

 removed before determining the color which 

 relates strictly to soluble matters. 



The odor should be observed in both hot 

 and cold samples, and the results recorded 

 in terms expressing quality and intensity, 

 substantially as described in the paper on 

 this subject pi-esented to this Section last 

 year. (Transactions A. P. H. A., 1899, p. 

 587.) 



Microscopical Examination. — The modified 

 Sedgwick-Rafter method appears to give 

 general satisfaction. The majority of an- 

 alysts express the results in ' Number of 

 Organisms per Cubic Centimeter,' but those 

 who have had the largest experience with 

 the method prefer to express the results in 

 ' Number of Standard Units per Cubic Cen- 

 timeter. ' Inasmuch as the latter method 

 takes into account the size of the various 

 organisms, and may also be used for the 

 amorphous matter, your Committee favors 

 the general adoption of the standard unit 

 method. 



Chemical Analysis. — So far as your Com- 

 mittee has been able to learn, the chemical 

 methods used for an ordinary sanitary anal- 

 ysis of a water do not vary very materially 

 in those laboratories where most of this 

 work is now being done. As a rule, the 



diflferences which are found appear to be 

 justified by the differences in the nature of 

 the waters and the objects of the work. It 

 appears, however, from general observation, 

 that there is room for improvement in a 

 number of laboratories in which water anal- 

 yses are made in small numbers and at 

 irregular intervals. The determinations 

 which from general opinion are considered 

 necessary for a satisfactory sanitary analy- 

 sis of an ordinary water are as follows : 

 residue on evaporation, total and dissolved, 

 with the loss on ignition in some instances ; 

 nitrogen as albuminoid and free ammonia, 

 nitrites and nitrates ; oxygen consumed ; 

 chlorine, and hardness. The general con- 

 sensus of opinion regarding these determi- 

 nations is quite harmonious on the whole, 

 and the best current practice may be out- 

 lined in brief terms as given beyond. 



Within the past few years water analysts 

 have had occasion to study types of water 

 about which very little was known a few 

 years ago, and to assist in a variety of 

 special problems relative to water pollu- 

 tion and various processes for the purifica- 

 tion of both water and sewage. Such in- 

 vestigations have naturally resulted in an 

 increase in our knowledge concerning a 

 number of analytical matters, about which 

 there was comparatively little known, in 

 practical terms, in this country, a dozen 

 years ago. Among the analytical methods 

 relative to these studies, of a more or less 

 special nature, may be mentioned those for 

 alkalinity, iron, sulphuric acid, carbonic 

 acid and dissolved oxygen. While the 

 methods for these and other determinations 

 have been carefully worked out with refer- 

 ence to certain conditions and waters of 

 certain types, it is felt by the Committee 

 that there are a number of details which 

 can to advantage be left in abeyance until 

 another year. The general trend relative 

 to these so-called special methods is out- 

 lined briefly beyond. 



