ANALYSIS OF POTABLE WATERS. 
G3’ 
We may also use 1 litre of water, 25 c.c. of baryta-water, and distil over 250 c.c. of water. 
The residue in the retort is filtered and separated from carbonate and sulphate of baryta, 
and then evaporated for subsequent determination of the nitrates by Pugh’s method 
(par. 12). Too much care cannot be taken in conducting these experiments on the 
amount of ammonia, for, owing to the condensation of ammoniacal salts upon glass 
vessels kept in a laboratory, unless much vigilance be exercised, an undue-proportion of 
ammonia is liable to be reported. 
The distillate is divided into two equal portions; one of these is submitted to Nessler’s 
test for ammonia in the following manner, as practised by Mr. Hadow:—Make a concen¬ 
trated solution of 1 ounce or more of corrosive sublimate ; having dissolved ounces of 
iodide of potassium in about 10 ounces of water, add to this the mercurial solution until 
the iodide of mercury ceases to be dissolved on agitation ; next dissolve G ounces of solid 
hydrate of potash in its own weight of water, and add it gradually to the iodized mercu¬ 
rial solution, stirring whilst the mixture is being made; then dilute the liquid with dis¬ 
tilled water till it measures 1 quart. When first prepared, it usually has a brown colour 
of greater or less intensity, owing to the presence of a little ammonia ; but, if set aside 
for a day or two, it becomes clear and nearly colourless; the clear liquid may then be de¬ 
canted for use. For a litre of the test liquid of equal strength, 62*5 grammes of iodide of 
potassium and 150 grammes of solid caustic potash will be required. About 50 grains (3 c.c.) 
of this solution are drawn off by a marked pipette and added to one-half of the distil¬ 
late ; if no ammonia be present, the mixture remains colourless, but if ammonia be pre¬ 
sent, the liquid will assume a yellowish tinge of greater or less intensity. The liquid 
will remain clear if the ammonia do not exceed one two-hundredth of a grain in the 5 
ounces, or about 0*25 mgrm. in 125 grms. of the distillate. The quantity of ammonia in 
such a case may be very accurately estimated in the following manner:—A solution of 
sal-ammoniac is prepared containing 3T7 grains of the salt in 10,000 grains of water 
(or 0*317 grammes of salt per litre), which is equivalent to one ten-thousandth of a grain 
of ammonia (H 3 N) in each grain of this solution, or 0*1 gramme in 1 litre. Suppose 
that a tint is obtained in the distilled liquid, which experience leads the observer to esti¬ 
mate, say at five thousandths of a grain ; 50 grains of the standard sal-ammoniac solu¬ 
tion are placed in a beaker, similar in size to that used for the distillate under trial, then 
diluted with 5 ounces of distilled water, previously ascertained to be free from ammonia 
(an impurity not unfrequently met with in the first portions of water which come over 
in distillation) ; lastly, 50 grains of the mercurial test-liquor are added. 
If the tint coincides in intensity with that furnished by the distillate, which has re¬ 
ceived an equal quantity of the mercurial test, the amount of ammonia may be con¬ 
sidered to correspond with that taken in the liquid for comparison. If the distillate ap¬ 
pear to have a deeper or a paler tint, a second approximative trial with a larger or a 
smaller quantity of sal-ammoniac must be made, and so on until the operator is satisfied 
that the tints coincide. On multiplying the number of grains of sal-ammoniac solution 
employed by 8 , the product will give, in ten-thousandths of a grain, the quantity of 
ammonia per gallon in the water under examination.-* When the quantity of ammonia 
exceeds the 20 th of a grain per gallon, or 0 *G mgrm. per litre, it is necessary to determine 
the amount by neutralization; and it was to provide for this contingency that the second 
half of the ammoniacal distillate was directed to be reserved. A test acid composed of 
2*882 grains of oil of vitriol in 1000 of water, or 2*882 grammes SO ;i ,HO diluted to 1 
litre, will contain an amount of acid, 1 grain of which will neutralize one ten-thou¬ 
sandth of a grain of ammonia, or 1 c.c. will be equivalent to 1 milligramme of H 3 N. 
The neutralization is effected in the ordinary way, using infusion of litmus to indicate 
the point of transition from alkalinity to commencing acidity. During the separation of 
ammonia from the water by the distillation with baryta as above directed, it will often 
happen that some peculiar or characteristic odour is developed, which may be of impor¬ 
tance as indicating some source of contamination which might otherwise be overlooked.- 
* Suppose that the observer estimates the amount of ammonia in the 125 c.c. on which he 
is operating at 0*25 mgrm., he takes 2*5 c.c. of the sal-ammoniac solution, and dilutes it with 
distilled water to 125 c.c.; he then adds 3 c.c. of the mercurial liquor, and compares it with the 
tint produced in the distillate by a like addition of the mercurial test. If the two tints corre¬ 
spond, multiply by 2 the number of c.c. of sal-ammoniac solution required, and the number ob¬ 
tained wall give the proportion of ammonia per litre in tenths of a milligramme. 
