62 
ANALYSIS OF POTABLE WATERS. 
The burette must be read off the instant the colour disappears, as on standing the blue 
tint returns. 
The columns headed E, F, G in the table given above refer to three successive trials of 
the same three waters; 0*05 gallon was mixed in E with 50 grains of dilute sulphuric 
acid, and exposed for three hours at ordinary temperatures with 50 grains of permanga¬ 
nate solution. F, a similar and simultaneous experiment, but employing TO grains’ of 
permanganate. G, a repetition of the experiment, using 100 grains of the solution of 
permanganate. H, I, K were three trials with the same waters on the following day 
acidulating in the same manner as before. In H, 80 grains of the permanganate solution 
was empioyed. I, Avas a second trial with 100 grains; K, with 150 grains of permanganate. 
The results of these and of numerous other experiments lead me to recommend that 
the permanganate be mixed in excess at once with the water acidulated with sulphuric 
acid, and that the experiment be continued without applying heat. At the end of three 
hours the excess of permanganate is to be determined by the aid of iodide of potassium, 
starch, and hyposulphite of soda. 
Various objections will naturally be raised to the use of the permanganate. It may be 
said—1st, That the quantity of permanganate required will vary Avith the kind of 
organic matter, so that the bulk of liquid decolorized will not necessarily be proportioned 
to the weight of the organic substance present. 2nd, That certain organic compounds 
may be absolutely or comparatively harmless, Avhile an equal weight of some other organic 
body m aetive putrescence may be seriously deleterious, and that the permanganate does 
not distinguish betiveen the two, so that a water which is comparatively harmless may 
even decolorize a larger amount of permanganateThan another Avater containing a dan¬ 
gerous amount of some septic poison. 3rd, That bodies not organic—such, for instance, 
as the nitrites—will bleach the permanganate. 
It may be replied that though this method, by the permanganate, is liable to these de- 
very same objections apply Avith ev r en greater force to the processes 
1 0 employed; and, further, that it is not improbable that the substances most 
i ^ oxlc “ ze( l are j us i ; those most likely to be injurious in their effects upon those who 
arinlc the water. Moreover, if nitrites are present, their action will be almost instanta¬ 
neous, Avhile that of the organic matter is gradual; besides which other tests Avill reveal 
the presence of nitrites. 
(9.) Gaseous Constituents. —Conjointly with these observations on the action of the 
permanganate, it is of considerable importance to determine the gaseous contents of a 
water and in particular the proportion of dissolved oxygen which it contains. I have 
aneady described in detail elsewhere an easy method of determining the amount of car- 
bomc acid, oxygen, and nitrogen in a water, sufficiently accurate for this purpose (see 
y e1 ??; ~hem. e< ^ - v °h & PP* 49 and 60). For this purpose, however, it is ne¬ 
cessary that the water be collected in glass stoppered bottles, filled as completely as pos¬ 
sible; and the determination of the gaseous contents should be performed Avithin twenty- 
lour hours, or at least not more than forty-eight hours after the water has been collected.* 
Whenever the proportion of oxygen is less than one-third that of the nitrogen, the 
water is to be looked upon as imperfectly aerated, the proportion in perfectly aerated 
water being, as is well known, oAving to the superior solubility of oxygen, that of 1 of 
oxygen to 2 of nitrogen. The proportion of carbonic acid in the mixed gas is de¬ 
termined by means of a concentrated solution of caustic potash, of sp. gr. 1*3, and the 
oxygen by the subsequent addition of pyrogallic acid (1 part of acid to 6 of water) as 
practised by Liebig. y ’ 
(10.) Estimation of Ammonia. —The determination of ammonia is a point of importance, 
put it may be readily effected as follows Into a capacious retort a quart of the v/ater 
is introduced, and the retort connected Avith a suitably-mounted Liebig’s condenser: an 
ounce of baryta-water is then added, and 10 ounces of water are distilled over slowly. 
. \ s . muc h to he Avislied that chemists would insist upon a greater uniformity in the Avay 
ot cofiectmg samples ot water for analysis. Glass bottles, well stoppered, should alone be used 
should* £1?°!?/ •?l n< T- aVe W W i\ ich are oftei L hut most improperly substituted for glass, 
should peremptorily be discarded. The stoneware is liable to introduce both sulphate of lime 
Salfc ■ Pers0us who collect the samples of water should be in 
, Gt h, to uns ® ( ) u . t t h e bottles thrice on the spot, and whenever it is practicable to submerge 
the bottle completely in taking the specimen. 
