284 
TYPHOID FEVER IN DISTRICT OF COLUMBIA. 
free and albuminoid ammonia and more nitrites and requires con- 
siderably more oxygen to oxidize the organic matter present in 
the water than we would expect of a safe and potable water. The 
quantity of chlorine is small, and in the present state of our knowl- 
edge regarding the normal chlorine for the Potomac watershed, 
throws but little, if any, light on the degree of pollution of Potomac 
water. According to information kindly furnished us by Mr. Leigh- 
ton, chief of the hydrograpliic division of the United States Geolog- 
ical Survey, many attempts have been made to determine the normal 
chlorine for the District of Columbia and the Potomac drainage area 
with but little success. In a letter dated November 27, 1906, he says: 
I feel fairly sure that the normal chlorine for the District is not far from three parts 
per million; yet our results vary from 1.6 to 7.8 parts. 
In view of these uncertainties regarding the normal chlorine, the 
amount of chlorine found in the Potomac water at the Dalecarlia 
inlet throws but little light on the subject under consideration — 
namely, the degree of pollution of the water of the Potomac. The 
quantity of nitrates is small, and the water is well aerated, contain- 
ing an average of 7.44 parts per million of dissolved oxygen, corre- 
sponding to 89.6 per cent saturation. Except after a heavy rain, 
the total solids left on evaporation are small. The residue from 
evaporation has always been found to char considerably on ignition, 
and the odor evolved on burning is something like that of burning 
wood, and also somewhat disagreeable. The turbidity, color, odor, 
and sediment var}^ greatly with the rainfall. After a long dry spell the 
water of the river is reasonablv clear, and at such seasons it shows 
only a slight turbidity and yields only a small amount of sediment on 
standing. After and during periods of heavy rainfall, however, the 
river is muddy and the turbidity of the water is great, and on stand- 
ing it yields a considerable amount of sediment, chieflj' clay. The 
odor of the uniiltered river water mav be described as eartlw or 
X/ 
woody, and during the period covered by our observations nothing 
particularly disagreeable or objectionable in the odor was observed. 
For the sake of comparison we have included in Tables 3, 4, and 5 
the results of analyses of Potomac water made by various analysts at 
different times, and also in Table 6 the analyses of the waters of 
a number of American rivers. It is evident from the results given in 
Table 4 that the water of the Potomac is liable to considerable varia- 
tion in the amounts of the several impurities. These variations can 
be readily understood when it is borne in mind that the Potomac 
drains a more or less greatly diversified, hilljr, and mountainous region, 
over which the rainfall varies greatly at different seasons of the year, 
and in fact during the same season. Casual inspection of the river is 
all that is required in order to form an idea of the extremely variable 
