430 



MEMOIRS OF THE NATIOJfAL ACADEMY OF SCIENCES. 



results. Bach mean or average determination of these four districts is indicated by a perpen- 

 dicnhir stripe or heavy broad line, showing- by its length the relative and approximate values of 

 that determination, and by its position the general time relations of the same. Stripes placed 

 directly above one another show that the determinations are of the same date. Tbe charts are 

 divided by vertical lines into spaces corresponding to the months which are named at the top. 

 Under the name of the month are given the inches of rainfall, and also the number of cases of 

 typhoid fever reported in the wards constituting the distribution districts during that mouth. 



In cases where a ward lies only partly in the district, the number of cases for the whole 

 ward is included in the calculation. The figures for the average rainfall, by months, have been 

 furnished by Mr. John L. Ogden, chief of the bureau of water, from the regular observations 

 conducted by his department on the watersheds of the water supply. For this and other 

 courtesies the writer wishes to here make his acknowledgments. 



The data of typhoid fever have been kindly given by Dr. J. How^ard Taylor, chief medical 

 inspector of the city board of health. 



A curve (Diagram V) has also been constructed from daily determinations, in duplicate and 

 triplicate, of the chlorine in the water of the laboratory (Table VII, Belmont district), extending, 

 with some iuterruptions, from September 27, 1892, to August 0, 18!I3. In those places where the 

 curve is deficient no determinations have been made. The monthly raiufall averages are given with 

 this curve, as in the charts. All chemical results are expressed in parts per hundred thousand. 



In the course of the work many accidents of various kinds have occurred, and of the deter- 

 minations affected some have been thrown out, while others have been retained, some judgment 

 being exercised in the matter. lu the results here given it has also happened in several cases 

 that doubt has arisen as to the dates of determinations or identity of samples and in the case of 

 the determiuatious of ammonia a slight confusion has arisen among distillates on two or three 

 occasions. 



The nitrogen as nitrites has been determined mainly on samples collected prior to January, 

 and has been found to vary from O.OOOO.") to 0.0013 parts per hundred thousand. This last number 

 was exceptional, most of the results being below 0.0005 parts per hundred thousand. 



With the idea of showing how the results of analyses of the water supply of Philadelphia 

 compare with those of the water supplies of New York City and of Boston, the table given below 

 has been prepared. The figures for the New York supply are taken from thirty-four cheuucal 

 analyses made by the city board of health at intervals of about a week or more, from the tirst 

 part of September, 1892, to the latter part of July, 1893, a period corresponding in general to 

 that occupied by the present investigation. In addition to the chemical analyses, twenty one 

 bacteriological estimations were made, generally at about the same intervals as the chemical 

 analyses, extending from the former date to the latter part of March, 1893. 



The data for the Boston supply are taken from the report of monthly analyses made of the 

 water from a faucet in the Massachusetts Institute of Technology in that city during the year 

 1891 and published in the report of the Massachusetts State Board of Health for that year. The 

 results of the examination of the Schuylkill are given separately from those of the Delaware. In 

 the case of the Schuylkill the figures are based on all the analyses of that water herein reported. 



For each of the cities the maximum and minimum and the average for each of the subjects of 

 analyses is given. 



It sliould be stated that the results for the nitrogen as nitrates in the New York water also 

 include the lutrogen as nitrites. 



[Results in parts per 100000.] 



