much smaller quantities: so that the goodness of water for drinking purposes I would estimate according to its permanent hardness rather than its temporary hardness.'

Pressed with other questions, the witness replied: for troops, in all cases we should prefer a soft water, if it were possible to obtain it.' 'Speaking generally, you are of opinion that the mere presence of carbonate of lime of 15 degrees of hardness would not be injurious to health? With 15 or 16 degrees of carbonate of lime hardness, I should say that it would be a hard water, and with some persons it would disagree and produce dyspepsia. I think it should not exceed 10 or 12 degrees, if possible. At the same time, I should wish to state that I would prefer water free from that even.'

For many years past we have never lost an occasion to advocate the use of soft water in preference to hard; and we have more than once treated of this important subject in the pages of 'Food, Water, and Air.'

The introduction of soft water for the use of towns and cities met with, at first, great opposition, and this from quarters whence it might have been the least expected; namely, on the part of some medical men and chemists. It was affirmed that the lime of the water was necessary to the growth of the bones, that without it they would become soft; and, indeed, that the whole frame without a powerful osseous skeleton would become weak and stunted. Those who made use of this argument forgot that phosphoric acid is as necessary to the bones as lime, and that water does not furnish a particle of this acid to the bones, it being obtained from the various articles of food consumed; and if a sufficient supply of phosphoric acid be obtainable from this source, why not the requisite quantity of lime?

For a long time this objection to the use of soft water prevailed, and prevented, in many cases, its introduction for the supply of towns. In some quarters the notion still lingers, and this groundless objection continues to be urged with pertinacity, especially where interest points to the use of hard water. That it is without any real foundation has now been proved by the experience of those towns which have for some years been supplied with soft water.

A further objection persistently urged against the employment of soft water for a town supply is the liability of such water to act on lead piping. But experience has also shown that this fear has been greatly exaggerated.

Liverpool, Manchester, Newcastle, and many other cities are now supplied with very soft water and this without any detriment to health.

Here then we have a large body of evidence of a very clear and convincing character all in favour of the use of a soft water.

It is therefore abundantly established that hard water is wasteful of soap in the washing of linen; that it renders the operation more laborious and less effective; that it is injurious to the linen it

self; that it is wasteful of soap in personal ablutions, besides being far less agreeable and efficient; and, in fact, that it is objectionable for cleansing purposes generally, and that it is a serious hindrance to the sanitary use and effects of such water.

THE SOFTENING OF WATER.

Many years since the late Professor Clarke, of Aberdeen, took out his well-known patent for softening water.

The principle of this process consists in adding a solution of caustic lime to the water to be softened. The effect of this is, to abstract a portion of the carbonic acid from the carbonate of lime in solution, both portions of lime being thus brought into the condition of a neutral carbonate, so little soluble is water, and which hence becomes gradually precipitated.

The water to be softened is divided into two portions, a larger one consisting of about three-fourths and a small one of one-fourth. The larger quantity is rendered decidedly alkaline by the addition of lime water, and then the second portion is added to it.

The quantity of lime water required is thus determined for each water for which the process is employed. The alkali may then be added with frequent stirring to the great bulk of the water to be softened, as contained in one or more reservoirs, lined with concrete. Care must be taken to render the water as nearly neutral as possible, as any excess of free lime would be very objectionable, and this may be guarded against by the employment, as indicator, of a solution of nitrate of mercury, added to a small quantity of the water, the black sub-oxide of mercury being thrown down on the addition of the alkali.

This process does not of course remove the lime from those combinations which give to water its permanent hardness; but since usually the greater portion of the hardness of a water is of the temporary character, it is in most instances highly effectual in the softening of a water, often removing nearly the whole of the hardness.

The Chemical Commission of 1851 recommended the adoption of this process to the Thames water with which London is supplied, and they estimated the cost at about 208. per million gallons of water.

The process has, in fact, been applied in several instances to the softening of the water supply of towns with very great success and advantage. And it may be said, in further recommendation of it, that it not merely softens the water, but that it also purifies it to a considerable extent, the carbonate of lime carrying down with it all the suspended organic matter, with but a small portion only of the dissolved organic matter.

The carbonate of lime obtained by this process should be collected, made into cakes and sold. It is often of a superior quality, and its sale would repay part of the cost of the process itself.

ON THE QUALITY OF WATER.

The quality of a water and its suitability or otherwise for domestic use depend first upon the nature and quantity of the several mineral constituents which enter into its composition, and secondly, on the organic ingredients, in solution, in suspension, or in the form of living organisms.

It has been shown that all the salts of lime and magnesia found in water render it hard, and therefore if they are present in considerable amount, the water is thereby rendered unsuitable for drinking, cooking, and washing.

Other mineral constituents of water, which, if present in anything like considerable amount, are to be viewed with suspicion, are the chlorides, especially chloride of sodium, and the sulphates, particularly sulphate of lime. The reason of this is, that while there are but few natural sources of sulphates and of chloride of sodium, they are abundantly contained in the excreta, and make their way into our drinking water either by percolation through the soil, or by being cast as sewage into our rivers and streams, which are too often the source of our water supplies. Dr. Angus Smith, in his evidence before the Royal Commission on Water Supply in 1869, thus refers to the occurrence of nitrates and chloride of sodium in waters. The nitrates, he says, 'are what I have called Old Organic Matter. Where nitrates are caused by matter from animals, there is always a corresponding amount of common salt. Men take from 200 to 300 grains at least of common salt every day, and it is given out every day. This is the most unchangeable accompaniment of sewage. Whenever chlorine is largely in water, it is necessary to look for nitrates derived from sewage; and, as a rule, it is so constant that there is scarcely any exception. When we find much more than the average quantity in a well-water, nitrates are found also, and if the water in a district is pretty well known-that is to say, if the amount of chlorine in water from any district is pretty well known, and a specimen of that water should indicate rather more chlorides than usual-you may conclude with almost certainty that it is from sewage.'

With regard to its organic constituents any considerable amount of albuminoid organic matter renders the water unfit for use, and the same may be said to a certain extent of the organic matter suspended in water, and especially of the living productions which impure waters so frequently contain in such abundance. But it must be remembered that in this latter case this dead and living organic matter is capable of being removed to a large extent by an efficient process of filtration.

Another circumstance to be taken into consideration in expressing an opinion as to the quality of a water supply are the fluctuations in

the amounts of the nitrogenous organic matter found in certain waters, especially river waters in summer and winter. These are shown in the analyses of Drs. Frankland and Odling, made for the Royal Commission on Water Supply, 1869, to be very great and remarkable.

The following causes appear to us to afford some explanation of this striking difference, and to account for the much larger quantity of albuminoid organic matter in winter. First, the streams and floods of winter which wash out the dykes and ditches in communication with the Thames; second, the death and decay of many forms of vegetable and animal life; third, the diminution in the amount of minute and infusorial life in the water; and, fourth, the slower decomposition and destruction of the organic matter in winter.

The presence likewise in considerable amounts of ammonia, nitrous, and nitric acids, derivatives of urea and albuminoid matter, would also serve, especially when taken in conjunction with other unfavourable results of analysis, to condemn a water. With respect to nitrous and nitric acids in water much has been said and written, and much discussion has taken place as to their significance and importance in potable waters.

PURIFICATION OF WATER.

Impure water, when left for a time, undergoes two different processes of purification. The one results from the decomposition of the organic matters contained in the water, and their breaking-up into ammonia, carbonic acid, sulphuretted hydrogen, &c.; the other is due to the oxidation of that matter, the oxygen being derived from the air continually absorbed by the water. This process of oxidation is, of course, greatly promoted by the motion and agitation of the water, as this brings the oxygen into more intimate contact with the organic matters in solution.

Both these methods, judged by their practical results, and especially the latter, are highly important; and were it not for them, disease resulting from the drinking of impure water would be of much more frequent occurrence than it now is, and it is only of late years that the importance of the purification of water by oxidation has been at all adequately recognised. But even now the extent and limits of its

operation are but ill defined, and exact experiments are still required to test its full value.

In reference to this question of the purification of water by oxidation, Dr. Letheby made the following statements in evidence given before the Royal Commission on Water Supply in 1869, when asked the question, Have you at all ascertained in what length of time or distance polluted matter will be decomposed and transformed in its chemical qualities; for example, supposing we had the sewage from Richmond poured into the Thames, how far down the river would it be lost as sewage and broken up into other chemical elements ?' he thus replied: "I have made a very great number of chemical experiments to determine that. I have examined most of the rivers in England, and this is the conclusion that has been come to, not only in my mind, but in the minds of all the engineers who have devoted their attention to this subject, that if ordinary sewage, containing, we will say, nearly 100 grains of solid matter per gallon, such as our London sewage, out of which probably something like 14 or 15 grains are organic, be mixed with twenty times its bulk of the ordinary river water and flows a dozen miles or so, there is not a particle of that sewage to be discovered by any chemical processes."

Mr. Wanklyn gave the following evidence before the Royal Commission in reference to the same matter. In reply to the observation: 'Q. 5482. It has been stated in evidence before us that if you pour into water a volume of sewage equal to 5 per cent. of the volume of water into which it is cast, the water will so operate upon it in deodorizing and destroying, and breaking up its elements-into its primitive elements, in fact-that it would no longer be sewage, or possess any of its noxious qualities. You apparently hold a contrary opinion?This I am sure of: the urea in the sewage in such a water would be very readily broken up into ammonia and carbonic acids, and a little exposure would dispose of the urea; but the albuminoid matter in sewage is extremely persistent, and one of the results of the whole investigation is this, that albuminoid matter is very persistent indeed, and you could not depend upon any treatment such as you have mentioned getting rid of the albuminoid matter.

5485. But will not certain changes take place even in the albuminoid matter?-Yes, certainly; but the change is very slow, and it is very irregular.'

Of the evidence of Dr. Frankland, the following questions and answers embrace the more important parts :—

'Q. 6222. What does your experience tell you is the effect of the quality of the present supply in London on the health of the population generally?-I cannot, of course, trace any direct connection between the present supply and the health of the population, but I consider that water contaminated with sewage contains that which is noxious to human health. There is no process practicable on a large scale by which the noxious material can be removed from water once