Page images
PDF
EPUB

Nitrogen Acids in Water.

69

Nitrous and Nitric Acids.—There is no reliable method for estimating nitrous acid. Add to an ounce of water one of dilute hydrochloric acid, or of acetic acid, a few drops of solution of iodide of potassium, and half an ounce of thin solution of starch. If there be much nitrous acid present a violet colour will be produced very soon-sometimes a deep violet colour is at once developed. When the nitrous acid is in minute quantity no coloura tion appears, even after the expiration of some hours. For the determination of nitrogen in the form of nitric and nitrous acids, there are several methods in use. Chapman's modification of Schulze's method is probably the best.

The process is carried out as follows:-50 c. c. of the water are introduced into a non-tubulated retort, and 50 to 70 c. c. of a solution of caustic soda added. The caustic soda must be free from nitrates, and the strength of the solution should be such that 1 litre contains 100 grm. of caustic soda. If necessary, the contents of the retort may be distilled until no ammonia comes over; that is, until the Nessler test is incapable of detecting ammonia in the distillate. The retort is now cooled, and a piece of aluminium' introduced into it (foil will answer very well with dilute solutions, but we much prefer thin sheet aluminium in all cases). The neck of the retort is now inclined a little upwards, and its mouth closed with a cork, through which passes the narrow end of a small tube filled with broken-up tobacco-pipe, wet either with water, or, better, with very dilute hydrochloric acid free from ammonia. This tube need not be more than an inch and a half long, nor larger than a goose-quill. It is connected with a second tube containing pumice-stone moistened with strong sulphuric acid. This last tube serves to prevent any ammonia from the air entering the apparatus, which is allowed to stand in this way for a few hours or over night. The contents of the pipe-clay tube are now washed into the retort with a little distilled water, and the retort adapted to a condenser, the other end of which dips beneath the surface of a little distilled water free from ammonia (about 70 to 80 c. c.) The contents of the retort are now distilled to about half their original volume; the distillate is made up to 150 c. c.; 50 c. c. of this are taken out, and the Nessler test added to them. If the colour so produced be not too strong, the estimation may be made at once; otherwise the remainder of the distillate must be diluted with the requisite quantity of

water.

Should it be desired to determine the ammonia by titration (alkalimetry), a much larger quantity of the water must be employed. Half a litre or a litre should be evaporated down to a small bulk, and treated in exactly the same manner, except that the distillate is received in standard acid instead of water.

The following rough method of estimating, or rather guessing, the amount of nitrates in water may prove of some use to health officers. Make a saturated solution of ferrous sulphate in 10 c. c. of the suspected water, and float it gently on strong sulphuric acid, contained in a narrow test tube. If there be much nitric acid present, a brown stratum will soon make its appearance at the juncture of the two liquids. Note the size and colour intensity of

1 A mixture of filings of iron and zinc may be substituted for aluminium, but not advantageously.-C. A. C.

Condensers are very apt to obtain a trace of ammonia if they have been standing all night, and must, therefore, be washed out with the utmost care. We prefer to distil a little water through them until ammonia can be no longer detected in the distillate.

[ocr errors]

70 Is Nitric Acid evidence of Water Impurity.

the strata produced in water containing 1, 2, 5, &c., grains per gallon of nitric acid, and compare results with those arrived at in the case of suspected waters.

Water in which the only nitrogen compound present is the harmless nitric acid is still regarded with suspicion by most sanitary chemists, from the supposition that the germs of disease in polluted water may survive the almost complete oxidation of the dead organic matter. When, therefore, large amounts of nitric acid are found in water, chemists, following the example of Frankland, pronounce the nitric acid to be evidence of " previous sewage contamination."

It is a fact that much larger amounts of nitrogen are found in water in the form of nitric acid than in that of ammonia or of organic matter; and I have no doubt that in limestone districts water which had never been contaminated with sewage often contains very large quantities of nitric acid. I have rarely found in a water obviously contaminated with sewage more than half a grain of organic and ammoniacal nitrogen per gallon, whilst in waters far removed from all obvious sources of animal impurities I have often detected from two to five grains of nitric acid per gallon. The waters of two pumps which I have constantly been testing for the last two years never contain sufficient ammonia to give the slightest colouration with Nessler's test, nor do they contain any nitrous acid, and yet they include enormous quantities of nitric acid. I have not the slightest doubt as to the wholesome character of these waters, notwithstanding the large quantities of nitric acid contained in them. This point is worthy of careful consideration. Is the nitric acid found in well water always derived in great part from effete animal matter? In the case of soft waters I have no doubt that the nitric acid present is derived from sewage. When we find a water containing only from four to ten grains of solid substances per gallon, we may safely regard the nitric acid present in it as evidence of previous sewage pollution; but the case is very different with hard waters-those most abundant in Ireland, and which contain from 20 to 150 grains of calcium and magnesium salts per gallon. In the presence of lime, and even of limestone (calcic carbonate, more or less impure), the decomposition of organic matter proceeds rapidly, and its nitrogen is soon converted into nitric acid. The soil possesses the power of retaining ammonia, alkaline phosphates, and most of the other materials which contribute to the nutrition of plants; but nitrates pass readily out of the soil, and are usually found (and often in large quantity) in the drainage water. Plants usually contain, when dried, about two per cent. of nitrogen; therefore the portions of them which decompose on or in the soil produce no inconsiderable amount of ammonia or nitric acid. The well water-which is simply drainage water-in limestone districts is, therefore, very likely to contain nitric acid (derived from decomposed vegetable matters), which the soil was not capable of retaining until appro

Nitric Acid in Waters.

71

priated by plants. I can also conceive that the nitric acid produced in the soil by the decay of manure, which is chiefly altered animal substances, and straw, may be carried into the wells, whilst the albuminoid nitrogen, ammonia, and other matters would be retained in the soil.

I frequently notice that water containing a large amount of nitric acid, but no other nitrogen compound, is almost completely free from chlorine. When water is unmistakeably contaminated with sewage, it invariably contains a large amount of chlorine, chiefly in the form of common salt. Water, however, may contain an abundance of chlorine, and yet be free from nitrogen in any form. The wells near the sea occasionally contain common salt; and in many parts of Ireland, and particularly in the city and county of Dublin, the well waters often include very large amounts of earthy chlorides. In a soft water, remote from the sea, the decided presence of chlorine and nitric acid should be considered as clear evidence of previous sewage pollution, and such water should be regarded as dangerous to health.

THE FOLLOWING TABLE SHOWS THE AMOUNT OF NITRIC ACID WHICH I HAVE FOUND IN SOME SPECIMENS OF PUMP WATER :—

An imperial gallon contains in grains:—

[blocks in formation]

The composition of the Waterford well water is so very peculiar that I think it desirable to give a somewhat detailed account of it here.

COMPOSITION OF THE WATER FROM A PUBLIC PUMP, WATERFORD. An imperial gallon contains:

[merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][ocr errors][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small]

The water was tolerably clear, but possessed a faint urinous odour. The chlorine was chiefly in combination with calcium and magnesium; and although the solids amounted to 70 grains per gallon, they did not include even a trace of calcic carbonate. I have looked in vain through the medical and scientific journals for the results of water examinations showing anything approaching to the enormous quantity of ammonia present in this remarkable water from Waterford.

72

Water Filtration.

CHAPTER VII.

PURIFICATION AND SOFTENING OF WATER.

[ocr errors]

Water is freed to a great extent from impurities suspended mechanically in it by filtration through sand. The water supplied to large towns is filtered in this way, but very often the filtering material is impure, and still more frequently it is kept too long in use without cleansing or renewal. Water filtered through animal charcoal is deprived of nearly all its organic matter. I have reduced the amount of organic matter (chiefly vegetable) in a waterpot 3-4 grains to 0-2 per gallon by filtering it through a layer of animal charcoal 2 inches in depth. It is, however, doubtful whether or not the germs of typhoid fever and Asiatic cholera which undoubtedly exist in water can be perfectly removed by filtration on a small scale; still, water which has been carefully filtered through a deep layer of animal charcoal is far less likely to possess zymotic power than the same water unfiltered. Frankland found that filtration of water containing "rice water"" discharges from cholera patients did not remove the poison of the disease.

Syphon Filter No. 1.

[graphic]

Syphon Filter No. 2.

The syphon filter consists of a block of charcoal, in the centre of which a tube is inserted. The block is placed in the water, and the latter percolates into the tube, from which it may be sucked out by a tube of vulcanized india rubber. The elastic tube may be filled with water and used in the ordinary manner of a syphon. Travellers would find a small syphon filter useful, as they might be obliged to drink water of a doubtful quality.

Messrs. Maguire and Son, Dawson-street, Dublin, prepare a very good charcoal filter, which I have found to work well. "Magnetic carbide of iron," wood and peat charcoals, and other materials are used in filter beds; but they are far inferior in purifying power to animal charcoal. Occasionally we meet with this substance in so impure a state that it renders the water passed through it undrinkable. It should be treated with hydrochloric acid (to dissolve the earthy salts which it contains), and washed repeatedly with water until the latter no longer acquires a disagreeable flavour from the charcoal. There is a great variety of filters on sale now, from

[blocks in formation]

the small syphon filter placed on the table to the large ten-gallon cylinder capable of filtering fifty gallons a-day. When a large quantity of water is to be filtered an arrangement such as that

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]

shown in the engraving may be employed. Every filtering bed of moderate size should be covered in.

Condy's liquid (solution of permanganate of potassium) may be used to destroy organic matter and sulphuretted hydrogen in water; it, however, often imparts to the water a brownish hue. It is doubtful whether or not permanganate has the power to destroy the germs of disease, supposing such bodies to exist, in the same way that it is known to destroy organic matter. It has little or no effect upon urea.

Alum may be used advantageously to precipitate the matters suspended in very muddy waters: from three to six grains per gallon of water may be used when there is reason to apprehend that water might possibly be contaminated with disease germs; then, if it must be used, the most effectual way to render it innocuous is to boil it for fifteen minutes. Water which has lost its gaseous constituents by boiling is very insipid; but to a great extent it may be aerated, by pouring it from one vessel into another for about thirty times.

Hardness. Water is said to be "hard" when it produces curds instead of a lather on treatment with soap. This hardness is due to the presence of earthy salts-chiefly chalk and gypsum. In many parts of Ireland the spring waters contain great quantities of magnesian and calcium salts. This is remarkably the case in Dublin city and county. The rock formation underlying the city and suburbs of Dublin is limestone mixed with black shale, and is known to geologists by the term calp. Resting on the solid rock. there is a stratum of impure limestone gravel, averaging about 40 feet in depth. In several parts of the bed of the river Dodder

F

« PreviousContinue »