Decbmbeb 14, 1900.] 



SCIENCE. 



909 



With regard to the limits of accuracy of 

 the several methods under various condi- 

 tions, the determinations which can be best 

 applied to various problems, the expression 

 of the results of analysis and the interpre" 

 tation of their results are all matters upon 

 which the Committee has nothing to say 

 until a further expression of experience and 

 views is received from members of the Sec- 

 tion. 



Residue on Evaporation. — The amount of 

 water used should be preferably such that 

 the residue will weigh from three to twelve 

 milligrams, although with sewages a greater 

 weight is allowable. Experience alone can 

 indicate the volume of water to be taken. 

 Relative to dissolved residue, the suspended 

 matter can be satisfactorily removed from 

 surface waters of the glacial drift formation 

 and from sewages by filtration through 

 filter paper. The sub-microscopic clay par- 

 ticles of the Southern and Western waters 

 can be best removed by a small Pasteur 

 filter. This is not wholly satisfactory, as 

 in some instances dissolved matters are ab- 

 sorbed by the filter, and in other cases they 

 are removed from those stored in the filter. 

 On an average it yields fair results, and no 

 improvement can be suggested at this time. 



With regard to the use of sodium car- 

 bonate, practice varies, but it would seem 

 to be wise to add it (with a deduction from 

 total weight) in those waters and sewages 

 in which it is of value to obtain the loss on 

 ignition. Evaporation is almost invariably 

 obtained iu a steam bath at a temperature 

 of nearly 100 degrees C. The loss on igni- 

 tion, it is believed, can be secured best with 

 the use of a radiator in accordance with 

 Drown's suggestions, although this device 

 is not in general use. In fact, there is 

 a growing tendency among workers to omit 

 this determination, except for sewages and 

 those waters relatively high in organic 

 matter. 



Chlorine. — This is determined always by 



titration with a standard solution of silver 

 nitrate, using potassium chromate as an in- 

 dicator. Colored surface waters first re- 

 quire decolorization by the addition of 

 aluminum hydrate. The volume of water 

 to be taken depends, of course, upon the 

 amount of chlorides present. With unpol- 

 luted surface waters in the East, from 200 

 to 250 cubic centimeters should be concen- 

 trated by evaporation. In the case of sew- 

 ages and highly polluted water containing 

 much organic matter, satisfactory results 

 can be obtained by evaporation to dryness, 

 ignition of the residue and subsequent solu- 

 tion of the chlorides with hot, distilled 

 water. The titration should be regularly 

 made with volumes substantially the same 

 as employed in the standardization of solu- 

 tions. 



Nitrogen as Free and Albuminoid Ammonia. 

 — The volume of ordinary water taken for 

 distillation is 500 cubic centimeters, and 

 with very highly polluted waters or sewages 

 smaller quantities are taken and diluted to 

 the above amount with ammonia- free dis- 

 tilled water. Where many sewages are an- 

 alyzed the volume taken may be 10 cubic 

 centimeters or less, in accordance with 

 Hazen's method. As a general rule, it 

 seems advisable to add a few drops of a 

 saturated solution of sodium carbonate be- 

 fore distillation. It is advisable to collect 

 the distillate in the Kessler tubes in which 

 this color is to be read. The rate of distil- 

 lation should be 50 cubic centimeters in 5 

 or 6 minutes. It is an almost universal 

 custom to collect three tubes of 50 cubic 

 centimeters each, for the free ammonia, and 

 five tubes for the albuminoid ammonia. In 

 regard to the preparation of alkaline per- 

 manganate and ISTessler solutions, the di- 

 rections in any good text-book may be 

 followed, and the individuality of various 

 workers in these particulars is apparently 

 not a factor affecting unfavorably the accu- 

 r&cj of results. Both the distillates and 



