anything but a disagreeable sensation, the water soon evaporates, and leaves a thin transparent artificial epidermis, which posesses a considerable degree of elasticity, and if not exposed to a cold temperature, it will not exfoliate until displaced by the formation of an epidermis beneath. I have used it in a number of cases, also on my own person, and have found it agreeable and effectual.

Lowell, Michigan, January 23.

Z. E. BLISS.

On the Analyses of Waters. By Prof. S. H. DOUGLASS, of the University of Michigan. A Report to the Board of Water Commissioners of the City of Detroit.

LABORATORY OF THE UNIVERSITY OF MICHIGAN,
February

To the Board of Water Commissioners of the City of Detroit.

GENTLEMEN-On the the tenth day of November last I received from J. Houghton, Esq., Superintendent of your City Water Works, three stoneware jugs, containing water from the following localities, viz.:

No. 1. From the iron pipe at the residence of A. C. McGraw, on Jefferson avenue, between Rivard and Russell streets, collected January 25th, 1854.

No. 2. From the wooden logs at the residence of Dennis Cuyle, corner of Orchard and Fifth streets, Crawford Park, collected October 5th, 1853.

No. 3. From a well at the residence of Amos T. Hall, on Woodward avenue, Park lot 11, collected October 5th, 1853. These waters were accompanied with a request to have them analyzed, and to report the result to you at my earliest convenience, with such suggestions, founded on the analyses, as I should conceive important to be taken into consideration in the construction of the new Water Works. Having completed the analyses, I herewith submit the result.

Before proceeding to consider the composition of the waters above named, it may not be inappropriate to make a few remarks on the varieties of water in common use for domestic purposes; the impurities of each variety, and the sources of those impurities.

These waters may be considered under three varieties.

First.-Rain water, which includes water derived from rain, dew, hail, snow, or frost. When secured before it has come in contact with the earth, or any substance that can impart impurities to it, this is the purest natural water. It contains only a small quantity of air, carbonic acid, and ammonia. Not holding in solution any of the earthy salts, its tendency to dissolve other material with which it may come in contact is very greatly increased. For this reason, as ordinarily secured, it is far more deleterious than any water in use. Thus falling upon tin roofs, and being conveyed by tin conductors, with lead soldering, to,cisterns, a very perceptible quantity of the poisonous compounds of the latter metal, derived from the soldering, are invariably found dissolved in the water. This I have found to be particularly the case with the water collected from roofs that have been painted with white lead. Collected from shingle or gravel roofs, the evil does not exist to the same extent; yet, in being conveyed through tin conductors, with lead soldering, or lead pipe, is clearly perceivable. I do not hesitate to say that rain water, collected in the ordinary mode, used as an habitual drink, must prove highly injurious to health.

Second.-River water. This stands next in purity to rain

water.

When its source is considered, it must be evident that the water of all rivers must be very far from being pure. The water of all our rivers, lakes, ponds, and oceans, has at one time existed in the air in a state of vapor, from whence it has been precipitated, in a pure state, as rain or snow. This water, coming in contact with the earth's surface, and frequently penetrating its strata, becomes impregnated with the soluble matter of each particular stratum. For instance, in leaching through a limestone or chalk formation, it would become charged with lime; or, in passing over a magnesian limestone, with lime

and magnesia. Thus it will be perceived that this second variety of water must contain variable ingredients; and that a Knowledge of the composition of the water becomes an index to the geology of a district, and a knowledge of the geology an index to the composition of the water.

Third.-Spring or well water.-Inasmuch as all the water of springs and wells has come in contact with, and leached through the earth, and usually very little time has been allowed for the separation of the clay, sand, &c., held mechanically in suspension, this variety may be considered the most impure water in use. This is more particularly the case with the water from wells dug in a clay soil, and in large towns, where surface filth accumulates in great abundance.

WATER AS A SOLVENT.

In what form of combination are these earthy salts held in solution? This is a question of some considerable practical importance, and one with which all should be familiar. In some few cases, the water dissolves the substance directly, as silica (sand) and the sulphate of lime (gypsum); while, in other cases, in order that the water should become a solvent, it must contain an excess of carbonic acid gas, or the salt must be in the form of a bi-carbonate. Thus pure water will dissolve little or no carbonate of lime (limestone), but allow the water to take carbonic acid, and convert the carbonate into a bi-carbonate; and it will readily dissolve a hundredth part of the limestone. It becomes a "hard water." By long exposure of this water to the air, or by boiling it, the free carbonic acid escapes as a gas; consequently, the water loses its power of holding the lime in solution. It becomes turbid and milky, and the lime is deposited. Hence, the calcarious deposits in the vicinity of "hard water" springs, and the calcarious incrustations on the inside of boilers. This carbonic acid is derived, in part, from the atmosphere, and in part from the soil. In the decay of vegetable matter, the carbon of the plant unites with the oxygen of the air, to form the acid. Hence, we find it very abundant in open, porous soils, highly charged with decaying organic

matter.

Water leached through such soils would acquire carbonic acid, and, coming in contact with limestone, would dissolve it in great quantity. A "hard water" would be formed. Boiling expels the carbonic acid, and the lime is no longer dissolved. The water is made soft. If, however, the water is made "hard" by the presence of the sulphate of lime, the sulphate is not affected by boiling. In this case, the lime may be precipitated by the addition of carbonate of soda or potassa. An insoluble carbonate of lime is formed and precipitated while the sulphuric acid unites with the soda. Hence, the great practical importance of knowing the precise condition of the lime held in solution—that is, whether it is a carbonate or sulphate.

Waters holding in solution the sulphates are liable to a form of spontaneous decomposition, highly deleterious to health, when they come in contact with organic matter, either animal or vegetable. All animal and vegetable matter contains hydrogen. In ordinary decomposition, this gas is liberated; and if, in the nascent state (at the moment of being set free from a previous combination), it comes in contact with the sulphates, it decomposes them, uniting with the sulphur, to form sulphuretted hydrogen, or hydro-sulphuric acid. This is a very noxious gas, and its foul odor is perceived in the exhalations from bilge water, cesspools, drains, &c. Hence the necessity of avoiding contact with organic matter when the water contains the soluble sulphates. It should not be conveyed through wooden logs, or pumped through wooden pumps. The disinfecting property of chloride of lime depends upon its power to decompose and destroy this hydro-sulphuric acid.

THE ANALYSIS.

In conducting any analysis, the first object with the chemist is, to determine what substances are present. This is called the qualitative examination, or analysis. In the case in question, an indefinite quantity was taken, and, having been divided into several parcels, the proper tests were applied for the detection of every substance liable to be present in natural or

Having thus fixed upon the presence of certain substances, attention was next directed to the determining of the quantity of each of these substances, or the quantitative analysis.

The total quantity of solid matter in a definite quantity of water, after filtration, was determined by evaporating to dryness 3500 grammes (nearly one gallon) over a water bath. The following table will give the result: