HOW SCIENCE HELPS TO KEEP US WELL
One branch of science—medical science—concerns itself almost entirely with health, but it would be out of place to refer to such matters here, even if the present writer were capable of doing justice to the subject. A new medicine or a new method of operating upon a suffering patient would be quite correctly described as a scientific marvel, but it is not of such that this chapter deals, but rather with those great works by which the engineer, often taught by the medical man, promotes the health of a whole community.
Most important of these, perhaps, is the provision of pure water. Some places are more fortunately situated than others in this respect, being near streams flowing down from mountains clear and unpolluted, which can be drunk after the minimum of purification. Others have to make use of the waters of a moderately clean river, as London does those of the Thames and Lea, in which cases the greatest care has to be exercised in the filtration of the liquid before it can be sent out through the mains for domestic consumption.
In this particular domain invention has been comparatively slow. There are novel pumps, it is true, for handling the water, such as the Humphrey Gas Pump, which the Metropolitan Water Board (London) have installed for filling their great reservoirs at Chingford. In these an explosion of gas is the motive force. Water flows by gravitation into a huge iron pipe closed at the top but open at the bottom. It is so arranged that a quantity of gas shall be entrapped in the upper end, which, being exploded by an electric spark, drives the mass of water out. Some of it, together with a quantity of fresh water, presently comes surging back, entrapping a fresh supply of gas and causing a new explosion; and so it goes on over and over again. The particular pumps at the waterworks referred to discharge about fourteen tons of water at each explosion, of which there are nine every minute.
The special effect of these machines, however, is not to improve the public health so much as to relieve the public pocket, for their chief feature is that they work more economically than any other kind of pump.
The filters, by which the water is purified, are simply layers of sand, much the same as have been in use for many years, although in some cases chemistry is brought in and the work of the filters aided by the action of precipitants. These are substances which combine in some way with the impurities in the water, and carry them to the bottom of the tank or reservoir, while the pure water remains to be drawn off from the top.
This is also the most usual method by which water is softened. Hardness in water is due to the presence of certain salts which are dissolved out of the ground as the water percolates through it, and which are absent from rain-water. To get rid of these the hard water has chemicals mixed with it in a tank, from which it flows slowly through another tank. The effect of the added chemicals is to convert the soluble salts in the water into insoluble particles, which then tend to fall down to the bottom of the containing vessel. The slow passage through the second tank is intended to give the particles time to settle.
Sectional View of Hydraulic Buffer and Running-out Presses of a 60-pounder Gun
Finally, to make sure that these have been all got rid of, the water traverses a filter, and then it is for all practical purposes as soft as rain-water. Some people are frightened of this artificially softened water, on the ground that chemicals have been added to it, supposing, apparently, that when they use such water they are really employing a chemical solution. That is quite wrong, however, for the added chemicals, combining with the "hardness," form substances which are quite easily extracted from the water altogether. If we liken the hardness to a number of pickpockets in a crowd, and the added chemicals to a number of policemen who come in to arrest the said pickpockets, finally leaving the crowd free from both pickpockets and policemen, we get a simple illustration of what takes place.
But almost equally important as the provision of pure water is the effective dealing with the drainage of a large town. Much offensive matter flows under the streets of our towns and cities, and if it is not to become a nuisance it must be scientifically dealt with.
Years ago the drains of London simply emptied themselves into the Thames, until, in 1864, two large drains were constructed, one on each side of, and approximately parallel with, the river, to intercept the old drains and to carry their contents to points many miles down towards the sea. Even that, however, by no means abated the evil, for it simply transferred it to a new place. The river was as foul as ever.
William Morris, in News from Nowhere, pictures the catching of salmon in the Thames off Chelsea, while one of London's prominent citizens, referring to what was being done in the direction of purifying the river, jocosely promised the members of Parliament a little fly-fishing at Westminster. Equally remote, it is to be feared, from actual accomplishment, these two prophecies do certainly indicate the tendency of events, for science has enabled the authorities to relieve the long-suffering river of much of the pollution which they used to thrust into it.
The first great step was the introduction, in 1887, of a treatment in principle very like that just described for softening water. The liquid from the drains is gathered into large reservoirs, where chemicals are added to it, causing the heavier matter to be precipitated in the form known as "sludge."
The liquid portion, or "effluent," as it is called, which is left is discharged into the river just as the tide is ebbing, so that it is carried right away, and, being comparatively inoffensive, it pollutes the river very little indeed. The sludge, on the other hand, is pumped into special steamers, which carry it down to a certain spot off the Thames Estuary, where they drop it into the sea. The currents at the particular spot chosen are such that none of it returns to the river.
For a similar purpose electrolysis has been employed. In this process the sewage is made to flow between two iron plates which are connected up to a source of electric current so that they form electrodes, while the sewage is the electrolyte. The current decomposes the liquid sewage, causing chlorine and oxygen to be deposited upon that plate which forms the anode. This deodorises and purifies the sewage, in addition to which iron salts are formed on the iron plates, the effect of which is to precipitate the solid particles. Thus the same result is achieved as when chemicals are used, the main difference being that instead of chemicals being added, they are produced by the passage of the current.
But, from the scientific point of view, the most interesting process of all is that in which bacteria or microbes are brought into the service. The fact is familiar to most people that there are certain minute organisms which cause terrible diseases. It is not so well known that there are still more of them whose action is extremely beneficent. The writer has seen these minute living things described in a popular book as "insects," but they really belong to a low order of plant life, and, as has been said in an earlier chapter, in spite of the lowliness of their status in the order of creation, they are able to accomplish certain chemical processes which baffle the cleverest men. They are particularly good, or some of them are at any rate, at forming compounds in which nitrogen forms a part. Further, they can be divided into two classes, the aerobic and the anaerobic. The former work best in air, while the latter need an absence of air while they perform their functions. After which preliminary explanation we can proceed to describe how they are induced to carry on this valuable work for mankind.
The sewage flows first of all into a tank from which light and air are excluded as far as possible. There the anaerobic microbes flourish and multiply, and in the course of their life work they convert the sewage into an inoffensive liquid. After an appropriate interval the liquid passes to filter-beds, where it trickles over and through beds of coke, the effect of which is to aerate it very thoroughly, whereby the aerobic microbes come into action, completing the good work, so that nothing is left except a clean, colourless and odourless liquid. Indeed it is more than that, for the microbes have turned the offensive matter into nitrogenous compounds which, as we have seen in a previous chapter, are the best fertilisers. Hence this effluent, if placed upon the soil, is of great value.
The advantage of this to towns which are not blessed, like London, with a broad river and the sea near at hand needs no explanation.
The bacteria necessary to carry on the process are always present in sewage, and after any particular plant has been in operation for a little while there results an accumulation of them, so that the process becomes more and more active as time goes on. Mechanical ingenuity has so arranged matters that a sewage disposal plant on this system can be made quite automatic, requiring little or no attention for months together, the raw sewage flowing in at one end, while the odourless, harmless effluent pours out at the other.
And, moreover, so powerful is the action of these beneficent bacteria that should disease germs come down in the sewage they soon destroy them. No chemicals are needed, for the bacteria replenish themselves. No sludge is left, everything being turned into the harmless effluent. And, it may be said once more, disease germs are destroyed. Of all the valuable inventions of modern times this is surely not one of the least.