Messrs Wanklyn and Chapman’s aluminium method is also a very convenient process. 2000 grains of the water are placed in a retort and half as much of a solution of 10 per cent. soda added. The soda solution is made from sodium soda and the absence of nitrates is secured by boiling the liquid with a piece of aluminium. Half the contents of the retort are distilled over and the residue cooled. A piece of aluminium foil of about six square inches area is tied to a piece of clean glass rod and sunk in the liquid. The neck of the retort is guarded by a tube containing fragments of glass moistened with hydrochloric acid; it is sloped, so that any liquid spurted into the neck will flow back into the retort. After resting several hours the neck of the retort is washed down with pure water, the contents of the tube are transferred to the retort, and the contents distilled over, down to about an ounce in two or three ounces water placed as a receiver. The contents of the receiver are made up to 200 grains and the ammonia is estimated in one half by Nessler’s test as below described.
An exceedingly accurate eudiometric method has also been devised by Dr Frankland, based on Crum’s observations, that a highly concentrated solution of nitrates, when vigorously agitated with mercury and an excess of concentrated pure sulphuric acid, yields all its nitrogen from the nitrates and nitrites, as nitric oxide, a compound occupying twice the volume of the nitrogen as nitrates. The weight of gas is easily calculated from the
volume measured (‘Journal Chem. Soc.,’ March, 1868).
Organic Contamination; means of estimating.—Messrs Wanklyn and Chapman’s method is most generally employed. It depends on the conversion of the nitrogen of the organic matter into ammonia and the employment of Nessler’s test to estimate this ammonia.
Nessler’s Test. 500 gr. of iodide of potassium are dissolved in a small quantity of hot distilled water, and to this is gradually added a cold saturated solution of mercuric chloride till the precipitate produced ceases to be dissolved upon stirring. To render this alkaline, add 2000 gr. of potassic hydrate and dilute the volume to 10,000 grain measures. A little more saturated mercuric chloride is added, and the whole allowed to settle, and the clear liquid decanted off. The test should have a slightly yellowish tint. If colourless, it is not sensitive, and more mercuric chloride must be added.
Standard Ammonia Solution.—Dissolve 27·164 gr. of pure sulphate of ammonium in 1 gall. of distilled water. For use dilute 100 gr. to 1000 gr. It will then contain 1 gr. of ammonia in 100,000 of water.
In order to estimate ammonia several six-ounce tall glass cylinders, free from colour, are graduated at 1000 grains. One of these is filled up to the graduation mark with the ammonia to be estimated, and about 30 gr. of Nessler’s reagent added from a pipette. The coloration produced is noted, a second cylinder is filled nearly to the mark with distilled water, and what is thought sufficient ammonia to produce a similar colour to the first run in, and the whole made up to 1000 gr., and 30 gr. of Nessler added; if after standing five minutes the colour in the second is the same as in the water examined, the quantity of ammonia they contain will be equal; but if this is not the case a second trial must be made, using more or less standard ammonia as the intensity of colour is greater or less than the first. After a little experience, more than two trials are rarely necessary.
Examination. (a) Free Ammonia. 7000 grains (a deci-gallon) of the water to be analysed is placed in a tabulated retort, and to it is added half an ounce of a supersaturated solution of carbonate of soda, made by dissolving ignited carbonate of soda in water free from ammonia. The contents are distilled over in two portions of 1000 grains each, and the second Nesslerised; if it contains no ammonia, the distillation may be stopped; if it does, the distillation must be continued and tested in portions of 500 grains till the ammonia no longer can be detected. If there is much ammonia in the cylinder of the second 1000 grains the first will probably contain too much to be conveniently estimated, and therefore an aliquot part diluted to 1000 grains with distilled water free from
ammonia should be used. The sum of the ammonia in these different portions multiplied by 10 gives grains per gallon.
(b) Albuminoid Ammonia. To the retort, after all the free ammonia has been driven off, one ounce of a solution of hydrate and permanganate of potassium of a strength of 2000 gr. of hydrate of potassium and 80 gr. of permanganate to 10,000 gr. of water is added, and the distillation continued until no more ammonia comes over, collecting the distillate in portions of 1000 c.c. as before. The sum is the albuminoid ammonia derived from the nitrogenous organic matter.