of Organic Matter in Potable Water. 11 
an end-reaction, and it is useless to expect a renewed precipi- 
tation in case the filtrate be submitted to second exposure. 
The precipitates are collected on asbestos filters, similar to 
those used in the determination of carbon in steel, washed 
first with water, then with strong ammonia to redissolve co- 
precipitated chloride, dissolved in nitric acid, evaporated to 
dryness, redissolved in nitric acid, and the silver determined 
by Pisanfs method. All these washings are but the work of 
a few minutes with the aid of a water-pump. The metallic 
silver may be weighed directly ; but the method indicated is 
more rapid and equally accurate. 
Six samples of the Philadelphia water (Nos. 230-235) were 
so treated ; and duplicate determinations of the oxygen re- 
quired to oxidize the organic matters were made by potassium 
permanganate. Finding that the results better accorded with 
the information imparted by the other data of water-analysis 
than those obtained by the permanganate, the method was 
systematically applied to the examination of the Passaic 
water (water-supply of Newark and Jersey City). 
The results were as follows : — 
Schuylkill Eiver. Cone- 
Silver sponding Oxygen by 
precipitate, to Oxygen. Permanganate 
mgrm. msrin. mgrm. 
Laboratory No. 230 1'47 0*218 0"18 
„ „ 231 1-65 0-244 019 
„ „ 232 1-91 0-283 0-18 
„ 233 2-02 0-299 018 
„ 234 1-56 0-231 0-16 
„ 235 1-39 0-206 016 
Passaic Eiver. 
,,242 2-26 0-33 0-34 
., 243 2-596 0-37 0-58 
244 2-3 0-34 0-56 
, 245 1-184 0-17 0-57 
246 2-296 0-34 0-59 
„ 247 3-59 0-53 1-05 
„ ,,248 2-074 0-31 0-33 
„ ,,249 3-333 0-49 133 
„ „ 250 2-592 0-37 037 
,. „ 251 3-55 0-52 0-37 
„ 252 3-2 0-47 0-38 
,,253 2-82 0-42 0'30 
255 2-29 0-34 0-35 
" 257 2-29 0-34 0-36 
, 256 2-67 0-39 0-36 
