280 
TYPHOID FEVER IN DISTRICT OF COLUMBIA. 
from July 30 to September 27, 1906, inclusive, from the Dalecarlia 
inlet and outlet, the outlet of the Georgetovm reservoir, the outlet of 
the Washington City reservoir, and the storage basin near the outlet. 
(2) Forty-nine specimens of tap water collected at various points 
over the city at dates indicated in Table 7, between July 16 and Sep- 
tember 28, 1906. 
(3) Twenty-three waters of deep wells. 
(4) Sixty- three waters of shallow wells. 
(5) Eleven specimens of water from small miscellaneous water 
supplies. 
(6) Twenty table waters. 
(7) Twenty-seven specimens of ice. 
(8) Twent}^ waters of wells connected with ice plants. 
In addition to this, duplicate determinations of chlorine, nitrites, 
and nitrates, and in many instances of total solids, have been made 
on all of the well waters, 86 in number, with the view of detecting 
any variation in the nature and amount of the impurities, and, as 
ma}^ be seen from Tables 8, 9, 10, 11, and 12 in the case of certain 
of the well waters, some of these determinations have been made 
several times and at different dates during the period covered by 
this investigation. 
OTHER CHEMICAL INVESTIGATIONS OF THE WATER SUPPLY OF 
THE DISTRICT OF COLUMBIA. 
Through the courtesy and cooperation of Doctor Woodward, 
Doctor Lynch’s analyses of the well waters of the District have been 
placed at our disposal, together with his (Lynch’s) analyses of a 
number of samples of ice manufactured in the District. We have 
also availed ourselves of the large amount of anatytical data on the 
Potomac water supply contained in Senate Document No. 259, Fifty- 
sixth Congress, first session, and in Senate Report No. 2380, Fifty- 
sixth Congress, second session, by Charles Moore, etc. 
In 1891 the well waters of the District, of which at that time there 
were 270, were very carefully analyzed by Clifford Richardson. The 
results of his investigations on this subject were published in the 
Journal of Analytical and Applied Chemistry (vol. 5 , pp. 1-36), and 
ordinarily would furnish valuable data for comparison, particularly 
as throwing light on the variation in the composition of the well 
waters during this comparative!}^ long period. Of the 270 wells 
existing at the time that Richardson made his analyses, however, by 
far the greater number have been closed and most of those now in 
use throughout the District have been opened since his analyses were 
made, so that comparatively few comparisons are possible. In a 
general way, however, his analyses show essentially the same con- 
dition of the water of the shallow wells that prevails to-day. He 
