73 
I have not yet had sufficient time to work out by my 
method the limits at which a water can be said to be unsafe 
to drink, but I hope to do so shortly. 
Example of analysis of sewage water from Devizes. 
(1) Ammonia process. 
Contains free ammonia 0*560 grains per gallon. 
„ albuminoid ammonia : 
1st distillate 1*435 „ 
2nd distillate 0*420 „ 
Total ammonia — 2*415 
= nitrogen 1*988 grains per gallon. 
The albuminoid ammonia in the first distillate was ob- 
tained by distilling in the usual way until no more ammonia 
could be estimated by Nessler’s reagent. The retort and 
apparatus was then carefully closed for the night and the 
contents distilled again next morning, the result being a 
second crop of ammonia (distillate No. 2). 
(2) Oxygen process. 
Oxygen required to oxydise organic matter, in grains per 
gallon 
in 3 minutes. 1 hour. 3 hours. 
1*862. 3*472. 5*48. 
5*48 grains of 0 = 4*1 1 grains of C. 
(3) Chromic acid process. 
(a) by titration with ferrous sulphate. 
250 c.c. of sample taken, added 20 c.c. of the chromic 
acid solution, and 10 c.c. of strong sulphuric acid, and boiled 
for 30 minutes, diluted to 1 litre, and took 100 c.c. of this 
solution with the standard ferrous sulphate solution, re- 
quired 19*0 c.c. of FeS 04 , therefore the whole litre would 
require 190 c.c. FeS 04 . 
20 c.c. of the chromic acid solution required, on being 
titrated, 210*0 c.c. of the ferrous sulphate solution. 
210-190 = 20 c.c. of FeS 04 (equal to the chromic acid 
reduced by the carbon in the water). 
Strength of the FeSOi solution. 
