MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 423 



in small, sterilized glass-stoppered bottles. The methods employed have been essentially the 

 same in all the analyses r(>ported, bnt in the conrse of the work the composition of the solution 

 nsed and the manner of carrying ont the different operations have varied in some cases, so that in 

 the following descrijjtions some of the ([nantities named have not always been employed, nor have 

 the details j^iven been followed up in all determinations. 



CHEMICAL METHODS. 



In a number of cases the samples have been filtered through Swedish tilter paper before 

 analysis. 



The chlorine has been determined by the method of Mohr, consisting in the use of a standard 

 solution of silver nitrate witli ixttassium chromate as indicator. 



(,)ne hundred cubic centimeters of water is taken for each determination, to which three dro^js 

 of a 10 i)er cent solution of potassium chromate are added. One-tenth of a cubic centimeter is 

 deducted for the end reaction from the amount of silver solution used. 



The solution of silver nitrate contains -t.7887 grams to 1,000 cc, and is standardized against 

 a solution of sodium chloride containing 1.C48 grams to 1,000 cc. One cubic centimeter of the 

 silver solution is very nearly e(iuivalent to L mg. of chlorine. The determinations have generally 

 been made in duplicate or triplicate. 



The oxygen consumed has been determined according to the principles of Kubel's method, 

 consisting in the measurement of the amount of a solution of potassium permanganate reduced 

 by a given volume of water in the presence of sulphuric acid at the boiling temj)eratuie. 



The operation is conducted in a porcelain caserole of about 250 cc. capacity, supported by an 

 iron ring over a Bunsen flame. One hundred cubic centimeters of the water, 5 cc. of a 25 per cent 

 solution of pure sulphuric acid, and about S cc. of a solution of ])otassium jiermanganate (0..3'J45 

 grams to 1,000 cc), standardized at the time of the analysis, against a solution of oxalic acid (0.7S75 

 grams to 1,000 cc), are placed in the caserole and boiled for approximately three minutes. At the 

 expiration of this time the flame is i-einoved and 10 cc. of the standard oxalic acid solution run 

 in from a pipette. 



Then more of the permanganate solution is added, until a faint red color is iiermanent. This 

 Solution is delivered from a Guy Lussac burette, by means of which the total amount used is read 

 off and one-tenth of a cubic centimeter deducted for the end reaction. 



The difference between this amount and the quantity of permanganate solution known to be 

 reduced by the 10 cc. of oxalic acid solution represents the amount decolorized or reduced bj' the 

 100 c<'. of water, and from this the oxygen consumed is calculated. The standardizing of the 

 permanganate solution is efl'ected in a manner similar to that above described for the determina- 

 tion, but about 100 cc. of distilled water is used in place of the sample. One cubic centimeter of 

 this solution of permanganate contains approximately 0.01 mg. of available oxygen. The deter- 

 minations have usually been made in duplicate, and about twenty-four hours after collection. For 

 some time the determinations have been carried on together, three casseroles being employed. It 

 is important in this operation that the sulphuric acid used should have little or no reducing efl'ect 

 on tlie permanganate. Such an acid seems to be unusual. That made by Baker & Adamson, of 

 Easton, I'a., has been found satisfactory. 



I II tlu^ determination of the free and albuminoid ammonia the Wauklyn i)rocess has been used. 



The distillations have been made from retorts of different capacities, and from round-bottomed 

 flasks, all conncH^ted with Liebig's condensers. 



The flasks are of 900 cc. capacity, with necks 11 cm. long, and the connections with the 

 condensers are made by means of corks and bent glass tubes, the apparatus being essentially like 

 that described by Drown. (EeportMass. Board of Health, 1890, jjt. 1.) 



^Vitll some exceptions, owing to accidents or other causes, the determinations have been made 

 ill duplicate throughout the systematic analyses. From November l-i to January 2 simultaneous 

 distillations were made from each sample of water, one from a retort and the other from a flask, 

 the latter being in connection with a condensing tube of block tin. 



After this time four samples of water were analyzed at once, and eight simultaneous distilla. 

 tious were made from every set of four samples. For this purpose, up to the 7th of April four 

 retorts and tour flasks were employed, three of the flasks being connected with tin condensing 



