910 



SCIENCE. 



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



the standard ammonia solutions should be 

 of, the same temperature before the addition 

 of the Nessler solution. 



Nitrogen as Nitrites. — No method superior 

 to the Warrington modification of the 

 Gness method is now known (see page 

 527, Special Keport, Mass. State Board of 

 Health, 1890, Part II.). 



Nitrogen as Nitrates. — -The determination 

 of nitrogen as nitrates is made almost ex- 

 clusively by two methods, the phenol-sul- 

 phonic acid method of Grandval and La- 

 joux, and the aluminum reduction method. 

 With waters comparatively high in nitrates, 

 and if a good brand of nitrogen-free caustic 

 soda can be obtained, the aluminum method 

 is more easily worked, and gives better 

 average results. With waters low in ni- 

 trates and low in chlorine, the phenol-sul- 

 phonic acid method gives as good or better 

 results than the reduction method. It is 

 intended to consider the comparative merits 

 of the two methods in detail in the later 

 report. 



Oxygen Consumed. — Practice varies widely 

 both here and abroad with reference to the 

 method for this determination ; and many 

 analysts omit it from the analyses of cer- 

 tain types of water. For sewages and 

 those waters which are high in organic 

 matter it undoubtedly yields valuable in- 

 formation. It would appear advisable to 

 adopt a uniform pi'ocedure intermediate 

 between the wide extremes now practiced. 

 Such would be afforded by the addition of 

 the reagents to the water when cold, and 

 boiling for five minutes. 



Hardness. — For ordinary sanitary work 

 the soap method is commonly used, and for 

 the soft Eastern waters it appears to give 

 reasonably satisfactory results. For the 

 hard waters of the West, Hehner's acid 

 method is preferred. There are some de- 

 tails connected with the determination of 

 the permanent hardness by the Hehner 

 method which require further study. 



Alkalinity. — This determination can be 

 satisfactorily made by Hehner's method. 

 Methyl orange is used by some workers as 

 an indicator, while recent comparative 

 studies give the preference to lacmoid or 

 erythrosine. The latter indicators have the 

 advantage, in connection with the use of 

 coagulants, of affording the most reliable 

 test for the presence of undecomposed alum 

 in water. 



Eelative to the latter point, the logwood 

 test is considered satisfactory by some 

 workers, while by others it seems to be 

 more of a qualitative test than a quantita- 

 tive one. The differences in opinion are 

 very likely due to unappreciated differences 

 in manipulation which require further 

 study. 



L-on. — There are evidently several meth- 

 ods of an allied nature which can be used 

 successfully for this determination, provided 

 they are carefully applied. In another re- 

 port the Committee can probably give a 

 graded set of procedures, applicable to 

 various conditions of practice. Thompson's 

 method as described in Sutton's ' Volumetric 

 Analysis ' appears to be most generally used. 



Sulphuric Acid. — Wildenstein's method as ■ 

 described by Ohlmuller has proved very 

 satisfactory for certain lines of work, and 

 preferable to the gravimetric method. 

 Whether or not this is true under a wide 

 range of conditions remains to be seen. 



Carhonic Acid. — For Eastern waters Pet- 

 tenkofer's method as described by Sutton is 

 considered to be generally satisfactory ; 

 while for the Western waters Trillich's 

 modification of this method, as described 

 by Ohlmuller, is preferred by some workers. 

 This method gives both the free and half- 

 combined carbonic acid. There is a grow- 

 ing tendency among chemists to attach the 

 more importance to the free carbonic acid 

 alone. This can be obtained differentially 

 by the method by which the free carbonic 

 acid is removed, by the passage of the water 



