STABLE DRAINAGE.

To 990 c. c. of this water, 10 c. c. of the drainage from a barn cellar were added. The cellar was not in a very filthy condition. The solution contained one per cent of the drainage and gave these results. The figures in parentheses show the additions made by the polluting substance:

A one per cent solution of sink-drain water was made with the

A one per cent solution of fresh urine was made with the same It analyzed with the following results:

water.

Odor

Color

Evaporation

Residue

Pungent or urinous
Milky and turbid
Quiet

Uniform but yellowish

Ignition of residue, it smokes, emits unpleasant odor, and blackens intensely.

A quite strong decoction of decaying apple-tree leaves was prepared and a one per cent solution of this made with the same water. It gave these results :

By comparing these results, it is noticed that foaming during evaporation is quite characteristic of vegetable pollution. Circles in the residue signify the same. All polluted waters do not give a residue that blackens strongly on ignition; the residue of some very bad waters scarcely darkens. The ratio of total solids to loss on ignition gives valuable evidence whether there is pollution. The ratio should not be less than 4, or 3 at the lowest, unless the total solids are below 5; then it may be somewhat lower. The ratio of fixed solids to hardness offers some testimony, as will be seen from the examples. The relation of hardness to alkalinity gives valuable evidence in some instances, and also gives good insight into the mineral constitution of the water. For instance: if the hardness and alkalinity are very nearly the same, both are caused by carbonate of lime or magnesia; if the hardness is greatly in excess of the alkalinity, it is mostly due to sulphates or chlorides of lime or magnesia; if the alkalinity is in excess of the hardness, then an alkali-carbonate is present, and sanitarily it might indicate pollution, for example, wash-water containing soap. (See example, sink water.) In the experiment with urine, if it had fermented, as is likely to be the case in actual pollution from vaults, the alkalinity would probably be in excess. Chlorine and nitrates are quite characteristic of pollution from animal matter and sewage, though it must not be inferred that a water is not contaminated from these sources, necessarily, even if it contains but very little of them. Ammonia and the oxygen consumed in oxidation furnish very valuable evidence of pollution.

The experiment with urine gave so much ammonia,and consumed so much time from the slow decomposition of urea, that it was not deemed necessary to complete it; portion after portion of the distillate continued to contain large quantities of ammonia. If fermentation had taken place, the results would have been quite different; a very large quantity of ammonia would have been evolved, but much more rapidly. From the experiment, it appears that iron may have some significance. All the polluted

samples contain more iron than the pure one, but as this metal is so generally and unevenly distributed in the soil, it would be hardly safe to attach much importance to it as a sign of contamination.

Using the results of these experiments, any one can calculate what results would have been obtained had any other given percentage of the polluting substance been taken, by dividing or multiplying the increment and adding the result to the uncontaminated water. Estimate the pollution from the stable drainage or sink water at one tenth of one per cent, and comparatively low figures are obtained. But who would care, knowingly, to drink water containing even this small amount of filth? I am convinced that the condemnation figures usually accepted have not been placed too low. A rigid adherence to figures still lower would add to both health and life.

The question of public water supplies deserves notice. Without doubt the supply of large cities is less likely to become much contaminated than that of smaller places, because greater vigilance is exercised by cities over their water supply. Many cities make an analysis of the public supply daily; consequently the first signs of unusual pollution are detected and action taken. But is the average city water supply sufficiently pure? A fair answer to the question may be obtained by comparing the vital statistics of one city with those of another. They show that those cities which are supplied with the purest water suffer least from typhoid fever and other diseases attributable to poor water; in other words, cities suffer from the diseases named nearly in proportion to the quality of the water with which they are supplied. About 60 per 100,000 of the inhabitants of Philadelphia die annually of typhoid fever; New York records about 25; Boston, about 40; Brooklyn, about 15. These numbers correspond to the purity of their water supply. Vienna, by changing from the polluted Danube to pure springs, reduced her cases of typhoid fever from 340 to 11 annually per 100,000 inhabitants. There is evidence enough that pure water saves life, and that the average city water is not sufficiently pure. Indeed, it is not to be believed that a standard for the purity of drinking-water can be obtained from natural water of ponds and rivers at all seasons of the year, although they receive no sewage, any more than it is to

be believed that it would be better for us to eat all our food raw. If our more sensitive nature and higher intelligence teach that it is better to prepare our food and not to take it as the brute does, should they not also teach the advisability of purifying our drinking-water if it is not already pure?

During a large part of the year, more or less vegetable matter exists in all open sources of water, as ponds and rivers. Decaying vegetable matter, if taken into the system, has its deleterious effects.

But how can water be purified in sufficient quantity for a city supply?

The best method in practical operation of which I have been informed is that at Antwerp, Belgium, of which the following is a description: At first they employed a method of filtering through spongy iron and sand, but soon abandoned it. tem of purifying water by agitation with iron and by sand filtration has been adopted with good results at Antwerp, where the water supply is taken from an impure source, the river Nethe. Large iron cylinders are mounted horizontally on hollow trunnions and a slow, rotating movement is given them by means of spur gearing. One pipe delivers the water into the cylinder against a disc which acts as a distributor. The outlet pipe is fitted with an inverted funnel up which the water passes so slowly as to allow the precipitation of the iron particles. The cylinders are filled to one tenth their capacity with iron borings. After the water leaves the outlet pipe, it is flowed through a sand filter.

The results of purifying water by this method have been stated by Mr. W. Anderson, as follows:

1. The chemical nature of the organic matter is changed, and existing albuminoid ammonia is reduced from one half to one fifth of its original amount.

2. The water is softened by the precipitation of the carbonate. 3. Infusorial life is largely destroyed and modified.

The area occupied by apparatus for dealing with 2,000,000 gallons per day is 29 feet by 24, and the cost of the iron consumed and for cleaning the filters is only $3 per million gallons. The cost of plant and apparatus having the capacity for 2,000,000 gallons per day is about $8,000.

Regarding the efficiency of the process, Mr. Anderson says