Note by Professor Clark, on the examination of water for towns, for its hardness, and the quantity of encrustation it deposits on boiling.

  • Thomas Clark
Date:
[1847]
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Licence: Public Domain Mark

Credit: Note by Professor Clark, on the examination of water for towns, for its hardness, and the quantity of encrustation it deposits on boiling. Source: Wellcome Collection.

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    DELICACY OF THE TESTS. For Hardness.—Suppose the Thames to yield a mean of 14° of Hardness. Carefully conducted experiments should then range between 140-1 and 130,9 of Hardness. That is to say, the mean result of more experiments than one should be within 0°T of the extremes; and it is to be remembered, that the Hardness of a water may be ascertained repeatedly within an hour. But 0°T of hardness is equivalent to one- tenth of a grain of Chalk per gallon; that is, 1 of Chalk in 700 thousand times its weight of water. But as the opera¬ tion is performed on only the 70th of a gallon, (1000 grains,) the whole weight of hardening matter that we actually operate upon in this experiment, is a 70th of 14 grains, that is, one-fifth of a grain; and the smallest weight we actually measure to, is the 70th of the 10th of a grain, that is, the 700th of a grain. I do not remember any process of equal quantitative delicacy, in the whole range of chemical analysis; and this one is the more remarkable as it is performed with Soap Test, previously known as almost the rudest and least determinate of chemical reagents. For Alcalinity.—If the Thames be at 14° of Hardness, it would probably yield 13°*1 of Alcalinity. Such a water, if tried according to the directions of the Specification, should give 130,1 of Alcalinity each time. The difference between the experiments, if carefully performed, should appear not on the first, but only on the second place of decimals. Now, since 1° of Alcalinity corresponds to one grain of Chalk per gallon, and since the Acid Test indicates less than 0o-l of Alcalinity, or one of Chaikin 700 thousand of water, we may safely infer that the Acid Test wil^jneasure one of Chalk in 1 million of water. Thus we obtain, for record, even more accurate results by the Acid Test than we do by the Soap Test. Nevertheless, the Soap Test is, in the abstract, the most delicate; for, although we use nearly the same quan¬ tity of each test, yet, in the case of the Acid Test, we act on the eighth of a gallon; whereas, in the case of the Soap Test, we act on only the 70th of a gallon. HOW TO MAKE THE FOREGOING PROCESSES AVAILABLE FOR ASCER¬ TAINING THE QUANTITY OF ENCRUSTATION TILE WATER DEPOSITS ON BOILING. For this purpose, the points to be ascertained are,— 1. The Hardness and the Alcalinity of a given water, unboiled. 2. The like particulars of the same water, after being boiled, without loss of steam for at least 2J hours, and then cooled, and (if necessary) filtered. From these indications, the weight per gallon of earthy deposit formed by boiling, if there be any, is deduced as follows.— Ch = hardness of unboiled. Let -j li' = ii ii boiled. (h — h' — H, that is, degrees of Hardness lost by boiling, occasioned by the precipitation of earthy salts, which may be either alcaline or neutral, or partly both. (a = alcalinity of unboiled. Let -j a' = H ii boiled. (a— a' = A, that, is, degrees of Alcalinity lost by boiling, occasioned by the precipitation of alcaline earthy salts. Note.—Observe that II is equal to A only in the case where all the precipitate is Chalk and Carbonate of Magnesia, which is but seldom the case. H — A = So much of the hardness lost by boiling, as is produced by the precipitation of neutral earthy salts. (-#—A) X 1*36 = B, that is, the above neutral earthy salts, calculated as dried Sulphate of Lime, in grains per gallon. Collected and represented in a Report, thus— Hardness of the Water {3^n.l)0?G(^ .... (Boiled,. Deposit by boiling, in grains, per gallon,— Alcaline earthy salts, calculated as Chalk, . . A Neutral earthy salts, calculated as dried Sul¬ phate of Lime,.B Total, .... A + B Alcalinity of the water When the alcalinity is only 1° or 2°, it is not worth while boiling the water, as haiijly any precipitation will take place. If you cannot conveniently arrange so as to boil the water without loss of steam, I recommend that you boil it with as little loss as possible, and, when the water has cooled, that you make up the loss in weight of the vessel and its contents, by adding distilled water. Mere boiling causes one change on the saline contents of the water. Boiling with evapora¬ tion causes an additional change. I recommend that the Alcalinity of a water be always stated by itself in a Report; that is, not mixed up with the Hardness: perhaps, indeed, it should be given in the Appendix to the Report; for persons not familiar with Chemistry are apt to be puzzled about the Alcalinity, whereas the degree of Hardness and weight of deposit per gallon, almost never give- them any difficulty. But the Alcalinity should not be alto¬ gether omitted from the Report, as the statement of it is necessary for a comparison of the results obtained by different Chemists. [Unboiled . (Boiled It will be for others to decide whether the ascertaining of the quantity of the deposit that a water forms on boiling, should or should not form a part of the Chemical Analysis serving to specify “ its adaptation for domestic and manu¬ facturing purposes,” as required by the Commissioners of Woods and Forests. t. a 2 Argyle Peace, Rothsay, Isle op Bute, 20th February, 1847.
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