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The Pamphlet Collection of Sir Robert Stout: Volume 32

Appendix

page 7

Appendix.

University Laboratory,

Sir—I have the honour to report on six samples of water forwarded to me for analysis by the Corporation of Dunedin.

The samples were taken from different sources. They were not collected under my superintendence, but I have no reason to doubt that they represent fairly the average quality of the water at the different localities.

For the sake of comparison with other waters supplied to large communities, I have transferred to my tables analyses of samples from various parts of the world. Those given in Table I. [herewith enclosed] are copied from the list given in Watts' "Chemical Dictionary" (page 1016, Vol. V., 1869). I have converted his milligrammes per litre into grains per gallon; and his calcium, magnesium, sodium, &c., into lime, magnesia, soda, &c.

The examples I have quoted in Table II., [enclosed], I have transferred from Wanklyn and Chapman's treatise on Water Analysis, published in 1870.

The analysis of each of the samples of Dunedin water reported on was performed by myself in all its details. I am, therefore, responsible for any inaccuracies it may contain. In the total amount of solid contents Dunedin supply approximates closely to the water of the Clyde, above Glasgow, the Elbe, the Spree, and the Danube, which supply Hamburg, Berlin, Vienna. It contains more than the Manchester supply, in the ratio of 3 to 2. It contains less than the London supply, in the ratio of 1 to 3.

In this respect, therefore, the water supplied to Dunedin is far within the limits of water extensively used for domestic supply. The softness of the Dunedin water is accounted for by the smallness of the quantity of lime and magnesia salts it contains. This softness is an advantage for washing and cooking purposes, and for domestic use in general; also for supplying steam-boilers, as it is not so liable as harder water to deposit a crust on the inner surface of the boiler.

A harder water, containing a larger proportion of sulphate of lime, would be more suitable for brewing purposes. There is, perceptibly, more iron dissolved in the water taken from the taps in Dunedin, than as taken from the "Lower Larger Reservoir." The quantity, however, is not such as to render the water in the least degree objectionable. The organic matter returned in Table I., is a constituent of a tar greater significance in a water intended for domestic use than any of the other constituents given in that table. Its amount was calculated in the usual way, from the loss sustained by ignition of the solid contents, due allowance being made for the carbonic acid and oxygen expelled. It will be seen on reference to the column headed "Organic Matter," in Table I., that the volatile organic matter in Dunedin water is approximately half as much as is contained in most of the water supplied to London, and nearly twice as much as contained in the Glasgow supply from Loch Katrine. I consider that on the whole it is not an excessive amount; and, when viewed in connection with columns headed "Ammonia," in Table II., it falls well within the returns reported for samples of water supplied to large communities.

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The most objectionable form of organic matter is that which contains Nitrogen or Nitrogenous organic matter. The proportion of this impurity that has already undergone decomposition is indicated in Table II., under the headings "Ammonia already formed," which might be called "Free Ammonia," and "Nitrogen of Nitrates and Nitrites." The amount of nitrogenous organic matter existing in the water, and still undecomposed, is stated in the same table, under the heading "Ammonia derivable from organic matter." A little less or more of this impurity makes a great difference in the quality of water. The objection to "Free Ammonia" and "Nitrates and Nitrites" is not founded so much on the injurious properties of the substances themselves as on the indication they give of the existence of nitrogenous impurities from which they have been derived. The Ammonia not yet formed, but whose constituents are contained in the nitrogenous organic matter still undecomposed, has been appropriately termed "Albuminoid Ammonia." On this "Albuminoid Ammonia chiefly depends the goodness or badness of a water intended for domestic use. Its amount is given in Table II., under the heading "Ammonia derivable from organic matter." It will be seen by reference to that table that the "Free Ammonia," or "Ammonia already formed, in the Dunedin water ranges from 0.01 to 0.08 parts in a million of water; the higher figure being quite exceptional, while the "Albuminoid Ammonia," or "Ammonia derivable from organic matter," is contained within the limits of 0.057 and 0.098 parts in a million parts of water.

By an enlargement of Table II., I might show, by additional examples, that the "Free Ammonia" in water supplied by the different London Companies ranges from 0.01 to 0.3 parts in a million; in the domestic supply of Manchester from 0.006 to 0.014 parts in a million; in the Edinburgh supply from 0.004 to 0.14; and in the Glasgow Loch Katrine water, as is seen by Table II., from .004 to . . . While the "Albuminoid Ammonia," or "Ammonia still unformed" ranges in the London supply from 0.05 to 0.16, in the Manchester supply from 0.06 to 0.10, in the Edinburgh supply from 0.034 to 0.10, and in Glasgow supply, Loch Katrine, 0.08.

The amount of Nitrates and Nitrites will be seen on reference to Table II. to be not unduly large in the Dunedin supply.

Under the microscope (Nachet's construction, 400 diamaters) the various samples submitted, while showing a considerable variety of organic forms, did not contain these in an unusual proportion, nor of such kinds as to render the water unfit for dietetic purposes.

On the whole, I consider the samples submitted for analysis a good soft water, well fitted for the domestic supply of a community.

I have the honour to be, Sir,

Your most obedient Servant,

James G. Black.

J. M. Massey, Esq., Town Clerk of Dunedin.