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]
Catalogue details

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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    NOTE ON THE EXAMINATION OF WATER FOR TOWNS, FOE ITS HARDNESS, AND FOE THE ENCRUSTATION IT DEPOSITS ON BOILING. PRIVATE CIRCULAR. PROFESSOR CLARK TO HIS CHEMICAL FRIENDS. At various times during the last few years, I have been applied to for information respecting methods I had adopt ed for examining Waters for Towns; but ill health has almost always prevented me from returning a satisfactory answer. There has been recently somewhat more occasion for such inquiries, in consequence of the Commissioners of Woods and Forests having been pleased to require, as one of the indispensable conditions to a Bill for supplying Water to a Town being presented by them to Parliament, that there shall be given in reference to the waters already supplied to the town, as well as in reference to the Waters proposed to be sup¬ plied,— “A statement of the quality of the Water as exhibited by chemical analysis, specifying its adaption for Domestic and Manufacturing Purposes, and its degree of hardness with reference to the Tests and Scale of Dr. Clark.” I take the liberty to write out one answer to all inquirers; and, imperfect as I am aware the information must be, I hope my friends will receive it with such indulgence as is due to an effort at affording information to others by a person confined to bed by illness, and unfit for any con¬ siderable exertion of mind. The processes alluded to for the examination of Waters are two—one for ascertaining the Hardness of Water; one for ascertaining the Alcalinity. Each of these processes is fully described in the Specifica¬ tion of a Patent, printed in the Number of the Repertory of Patent Inventions for October, 1841. (Hodson, Publisher, 112 Fleet-Street, London.) Vol. 16, p. 225. A water is, indeed, most materially affected in its fitness for domestic uses and manufacturing purposes, by the degree of its hardness. But many hard waters have the additional objection of depositing earthy matter on being boiled. This matter forms an encrustation on the boiler, and fills up tubes employed in giving passage to the heated water. In this land of steam-engines, it need not he told how annoying this quality is. Not only should the chemist be able to tell, ay or no, whether any such deposit will be formed; but, when one does occur, it is desirable to know how much altogether, and how much of each of the more important kinds of matter, will be deposited. Now, in the Specification alluded to, there is no express direction given for obtaining this impor¬ tant point of information; because this was not necessary to | the invention there described; neither, indeed, had I then contrived a method for the purpose. But ever since Sep¬ tember, 1845, I have been accustomed to derive this infor¬ mation from the hardness and the alcalinity of the water boiled and unboiled. To explain the method of deducing this information, is a principal object of the present Note. Referring to the Specification, I begin by describing a few improvements that have been suggested by experience, since the Specification was enrolled. PROCESS FOR ASCERTAINING THE HARDNESS OF WATER. In June, 1843, having occasionally before met with some few specimens of waters, and more especially soft waters from springs, where the indications of the Soap Test, which in general are remarkably distinct, were obscure, I discovered the cause of this obscurity to be an excess of Carbonic Acid; that is, an excess over ami above what is necessary to form alcaline or earthy Bicarbonates. This excess has the pro¬ perty of slowly decomposing a lather once formed. For the purpose of guarding against an excess of Carbonic Acid in all cases, I recommend that before you measure out the water for trial, you shake it briskly in a stoppered glass bottle half filled with it, sucking out the air from the bottle at intervals by means of a glass tube, so as to change the atmosphere in the bottle. In all trials of waters above 16° hardness, not only should such waters, and the distilled water to be used along with them in the trials, be treated in this manner, previous to their being measured out and mixed, but the measured mixtures themselves should be treated in like manner, before any Soap Test is added to them. The Soap Test itself should be occasionally so treated before it is measured out. To obtain uniform results with the Soap Test, I recom¬ mend that as soon as you observe that a lather is formed, such as will remain all over the surface of the water for five minutes, you take a note, but only an interim one, of the quantity of the Soap Test that has been added. In about half an hour you should shake the bottle again, to see whether the lather will still remain for five minutes. If the water under trial do not exceed 4° or 5° of hardness, it is likely to require a little more Soap Test upon this renewed shaking; but in every case where more Soap Test is required, let more be added to the water. This latter quantity and the former will together make up the whole Soap Test that is to determine the hardness of the water under trial. For hours afterwards, unless perhaps the water do not exceed 1° or 2° of hardness, j a lather lasting for five minutes may be restored by your shaking the phial. This mode of procedure, by producing a lather whose permanence we may repeatedly verify, wall conduce much to the uniformity and accuracy of our trials.
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