456 Scientific Proceedings, Royal Dublin Society. 
only complicates the operation, but renders a special apparatus 
necessary, and unfits the process for “ field ” work. 
The amount of dissolved oxygen which a water contains either 
originally or which it loses on keeping—and especially the latter— 
is probably a more important criterion of what may be termed 
‘“‘active ” pollution than any other ;! and some simple and efficient 
method of determination which can be used by the ordinary ana- 
lyst, and if necessary, at the place where the sample is collected, 
seemed to the authors to be a desideratum of importance. 
In the process which they have devised for the purpose, the 
simplest apparatus is used, as well as the most ordinary reagents 
to be found in any chemical laboratory. No inactive gas is 
necessary, and the titration is performed in an open dish. The 
whole process, in fact, is one which a person of ordinary intelligence, 
and without any special chemical training, could be easily taught 
to perform. Its principle is simple, and consists in absorbing the 
dissolved oxygen in a measured volume of the water by ferrous 
sulphate and excess of ammonia in a vessel completely filled with 
the three, and closed both when mixing them and during the 
period necessary for the oxygen absorption. Sulphuric acid is then 
added in excess in such a way that no air gains admission during 
the process, after which the mixture is transferred to an open dish 
and there titrated either with permanganate or bichromate.2 The 
details of the process are as follows :— 
SranparpD Soiutions.—(1) Ferrous Sulphate.—About 12 
grammes of the crystallized salt are dissolved in 250 c.c. of dis- 
tilled water. Theoretically, 12:444 grammes give a solution, each 
1 See the highly important paper of Dr. W. E. Adeney on this subject, Roy. Dublin 
Soc. Trans. 5 (series 2), [1895], p. 539. 
2The principle of absorbing the dissolved oxygen in water by ferrous sulphate 
and an alkali, with subsequent determination of the unoxidized ferrous salt in the 
acidulated mixture by permanganate, is an old one, and was first employed, we believe, 
by Mohr (Lehrbuch d. Titrirmethoden yon Fr. Mohr, 4 Aufl., p. 239). The method 
as carried out according to his directions is, however, open to several sources of error, 
which we have sought to eliminate in the process here described. 
This opportunity may be taken to refer to papers by Adams (Chem. Soc. Journ. 
Trans., 61 [1892], p. 310), Blarez (Journ. de Pharm. [5], 18, p. 55), and apparently 
Latieu also (Journ. Pharm. Anvers [1887], p. 570), on methods for the determination 
of the dissolved oxygen in water, in which the use of an inactive gas is avoided. 
