Page images
PDF
EPUB

A NEW PROCESS

FOR

PURIFYING THE WATERS

SUPPLIED TO THE METROPOLIS

BY THE EXISTING WATER COMPANIES:

RENDERING EACH WATER MUCH softer,

PREVENTING A FUR ON BOILING,

SEPARATING VEGETATING AND COLOURING MATTER,

DESTROYING NUMEROUS WATER-INSECTS,

AND

WITHDRAWING FROM SOLUTION

LARGE QUANTITIES OF SOLID MATTER,

NOT SEPARABLE BY MERE FILTRATION.

BY THOMAS CLARK,

FROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF ABERDEEN.

21.

LONDON:

PUBLISHED BY RICHARD AND JOHN E. TAYLOR,

RED LION COURT, FLEET STREET.

1841.

[Price Sixpence.]

Gough, Add! London

[graphic][merged small][merged small]

A NEW PROCESS

FOR

PURIFYING WATER.

On the 8th of March last, Her Majesty's Letters Patent for Invention were granted "to Thomas Clark, Professor of Chemistry in Marischal College, University of Aberdeen, for a new mode of rendering certain waters (the water of the Thames being among the number) less impure and less hard, for the supply and use of manufactories, villages, towns and cities."

This patented invention, which attempts and accomplishes more than has ever been so much as aimed at by any of the recent numerous projects for procuring better water for the metropolis, is peculiarly applicable to the improvement of the waters that are supplied by the several Water Companies. Intending to make the invention available to the inhabitants of the metropolis, and wishing to do so through the existing Water Companies, the Patentee begs leave to submit, for the consideration of the Directors and of the public, so much general explanation as will afford an idea of the nature of the process, and of the advantages to be expected from its adoption. Minute scientific elucidations and practical details are not required in such an explanation; but both will be cheerfully communicated whenever a proper occasion shall arise.

A 2

Theory of the Process.

To understand the nature of the process, it will be necessary to advert, in a general way, to a few long-known chemical properties of the familiar substance chalk; for chalk at once forms the bulk of the chemical impurity that the process will separate from water, and is the material whence the ingredient for effecting the separation will be obtained.

In water, chalk is almost or altogether insoluble; but it may be rendered soluble by either of two processes of a very opposite kind. When burned, as in a kiln, chalk loses weight. If dry and pure, only nine ounces will remain out of a pound of sixteen ounces. These nine ounces will be soluble in water, but they will require not less than forty gallons of water for entire solution. Burnt chalk is called caustic lime, and water holding caustic lime in solution is called lime-water. The solution thus named is perfectly clear and colourless.

The seven ounces lost by a pound of chalk on being burned, consist of carbonic acid gas-that gas which, being dissolved under compression by water, forms what is called soda water.

The other mode of rendering chalk soluble in water is nearly the reverse. In the former mode, a pound of pure chalk becomes dissolved in water in consequence of losing seven ounces of carbonic acid. To dissolve in the second mode, not only must the pound of chalk not lose the seven ounces of carbonic acid that it contains, but it must combine with seven additional ounces of that acid. In such a state of combination, chalk exists in the waters of London -dissolved, invisible, and colourless, like salt in water. A pound of chalk, dissolved in 500 gallons of water by seven ounces of carbonic acid, would form a solution not sensibly different, in ordinary use, from the filtered water of the Thames, in the average state of that river. Chalk, which

THEORY OF THE PROCESS.

5

chemists call carbonate of lime, becomes what they call bicarbonate of lime, when it is dissolved in water by carbonic acid.

Any lime-water may be mixed with another, and any solution of bicarbonate of lime with another, without any change being produced: the clearness of the mixed solutions would be undisturbed. Not so, however, if lime-water be mixed with a solution of bicarbonate of lime : very soon a haziness appears; this deepens into a whiteness, and the mixture soon acquires the appearance of a well-mixed whitewash. When the white matter ceases to be produced, it subsides, and in process of time leaves the water above perfectly clear. The subsided matter is nothing but chalk.

What occurs in this operation will be understood, if we suppose that one pound of chalk, after being burned to nine ounces of caustic lime, is dissolved, so as to form forty gallons of lime-water; that another pound is dissolved by seven ounces of extra-carbonic acid, so as to form 500 gallons of a solution of bicarbonate of lime; and that the two solutions are mixed, making up together 540 gallons. The nine ounces of caustic lime from the one pound of chalk unites with the seven extra ounces of carbonic acid that hold the other pound of chalk in solution. These nine ounces of caustic lime and seven ounces of carbonic acid form sixteen ounces, that is, one pound of chalk, which, being insoluble in water, becomes visible, at the same time that the other pound of chalk, being deprived of the extra seven ounces of carbonic acid that kept it in solution, reappears. Both pounds of chalk will be found at the bottom after subsidence. The 540 gallons of water will remain above, clear and colourless, without holding in solution any sensible quantity either of caustic lime or of bicarbonate of lime.

This will give a sufficient idea of the theory of the patented process. The rules, the precautions, and the details neces

« PreviousContinue »