358 
TYPHOID FEVER IX DISTRICT OF COLUMBIA. 
Table 21. — Chemical improvement of Potomac water as the result of filtration. 
[Compiled from analyses made in the laboratory of the filtration plant, covering a period of 20 ,>eeks. 
from February 13 to June 26, 1906, and given in annual report of Captain Cosby, Corps of Engi- 
neers.] 
Turbid- 
ity. 
Chlo- 
rine. 
Ammonia. 
( 
Ni- 
trates. 
Dis- 
Per 
cent of 
satura- 
tion. 
Reservoir. 
Free. 
Albu- 
minoid. 
Nitrites. 
solved 
oxygen. 
Washington Citv 
31.0 
1.6 
0. 015 
0.073 
0.0028 
0.79 
9.72 
94.4 
Storage basin 
40 
1.6 
.010 
.041 
.0004 
.92 
8.10 
78.2 
Improvement in parts 
per miUion 
Improvement in j)er cent 
27.0 
87. 1 
.005 
33.3 
.032 
4.3.8 
.0024 
85. 7 
Table 22. — Chemical improvement of Potomac u'o.ter as the result of subsidence and 
filtration. 
[Compiled from analyses made in the division of chemistry of the Hygienic Laboratory, covering a 
period of 11 weeks, from July 16 to September 28, 1906.] 
Reservoir. 
>> 
Total solids. 
Cliloriiie. 
Ammonia. 
> d 
X — o 
S. - ^ 
— w ^ 
3 3: 2 
'f, - 
'^5 Sc 5 
^ ^ X 
2- X >-S 
-3 
i % 
> S 
1 
Dalecarlia, inlet 
221.0 
203.0 
156 
47.1 
2.6 
0. 024 
0. 161 
0. 0031 7. 44 
89. 6 4. 1 
Storage basin 
46 
127.0 
88 
39 
2.53 
.015 
.0.54 
. 0003 5. 87 
71.4 2.0 
Improvement in 
parts per million . . 
216. 4 
76.0 
63 
8.1 
.07 
.009 
.107 
.0028 
2. 1 
Improvement in i>er cent. . 
97.9 
37.4 
43.6 
17.1 
2. 7 
37. 5 
66.0 
90. 0 
51.0 
1 
a Average of all readings made. 
Dissolved oxygen consumed in oxidation, 21 per cent. 
Table 23. — Chemical improvement of Potomac water as the result of subsidence and 
filtration. 
Compiled from analyses made in the laboratory of the filtration plant, covering a period of 20 weeks, 
from February 13,1906, to June 26, 1906, and given in annual report of Captain Cosby, Corps of Engi- 
neers.] 
Reservoir. 
Tur- 
bidity. 
Chlo- 
rine. 
Ami 
Free. 
monia. 
Albumi- 
noid. 
Nitrites. 
Dissolved 
oxygen. 
Per cent 
of satu- 
ration. 
Dalecarlia, inlet 
Washington Citv reservoir 
223.0 
2.0 
0. 032 
0. 244 
0. 00.33 
9. 72 
8. 10' 
(“) 
94.4 
78.2 
Storage basin, filtered 
Improvement in parts per mil- 
lion 
Improvement in per cent 
4.0 
1.6 
.010 
.041 
.0004 
219.0 
' 98.7 
0. 4 
20.0 
.022 
69.0 
.203 
83.0 
.0029 
87.9 
Dissolved oxygen consumed in oxidation, 16.7 per cent. 
aAccording to analyses given in Captain Cosby’s report the dissolved oxygen was determined only in 
the Washington City reservoir and in the filtered water of the storage basin. It may be observed, 
however, in this connection that the amount of dissolved oxygen suffers but little change in passing 
through the several reservoirs until the water passes through the sand filters, when it is reduced from 
16.7 to 21 per cent. 
