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The first three are well known tanks referred to in my first paper; Ramdhone Ghose's Tank, Jaun Bazar, is that also noticed there,* near Mr. Dall's school, the water of which has since become much cleaner, and the Baranagar Tank is also that referred to there, the well being an old one on my own premises.

As to the remainder, some explanation is necessary. requested by the Municipal authorities in December last to examine some waters in the northern part of the town, with reference to a proposed public tank to be excavated there, and the results are included in the table. Of these Nyan Chund Dutt's Lane Tank and Well and Blaquiere's Tank are old sources of supply; the three latter "wells" were simply holes dug in the ground 8 or 9 feet deep to collect water for examination: the water from the aqueduct was supplied at my request for comparison.

Another table will exhibit a few more points for comparison.

* Called Dhurrumtollah Tank by mistake.

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And to get a full insight into the nature of such waters, a complete analysis was made of two of them, of which this is the result for 100,000 fluid grains of water.

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Phosphoric acid: very distinct indications of in both.

This was also found in smaller quantity in the other four of these waters, and in still smaller quantity in the water of the aqueduct.

The relative proportions of these constituents, so different from those of ordinary spring or even river waters, point clearly to their origin. The large quantity of alkaline salts, compared with those of Lime and Magnesia, and the large proportion of Potash and of organic matter, indicate that they are derived from the decomposition of vegetable and animal substances: the phosphoric acid and perhaps the chlorine being more particularly characteristic of their animal origin. In fact, it is the composition of sewage water, and differs from some other analyses of English town sewage* most remarkably in the large proportion of potash present, no doubt the product of the vegetable food of the mass of the population. It is indeed simply sewage water, deprived in great part of its bad smell by filtering through the earth. And the partial analyses of the other tanks and wells (except the three first tanks of the table) indicate that the waters all partake more or less of the same character, and contrast strikingly with the superior purity and different characteristics of the river water during the cold season.

The large quantity of Ammonia as exhibited by Table VIII. in the two waters fully analysed is also very striking.

Now to return to the consideration of the organic matter which has undergone comparatively little change, and for the proper examination of which we have no very ready or suitable chemical processes: the best means of judging of its nature and properties have already been discussed in my first paper. These are, chiefly, the general appearance and smell of the residue obtained by evaporating the water, the smell on burning, and the estimation of the amount of nitrogen by the Soda lime process. This last, for reasons already stated, I have not applied. But I may observe again, that these bad tank waters more resemble the river water of the rains than of the hot season, in the appearance and properties of their organic contents. No doubt this proceeds in part from the larger proportion of matter of vegetable

Lawes and Gilbert, Journal of Chem. Soc. Ser. 2, Vol. IV. p. 118 for 1866. Way's Report on Sewage of Towns quoted in Parkes's, Manual of Practical Hygiene, 2nd edition, 1866, p. 325.

nature; non-nitrogenised matter. It appears to me, however, that there is a tendency generally to make too much of this distinction between matter of vegetable and of animal origin, it being often. spoken of as if the organic matter were of little importance, if it could be shown to be vegetable matter. Now it may be admitted that most probably water tinged by peaty matter consisting of the ordinary humous class of acids and salts, may be not at all even injurious to health, and that water flowing over or percolating through the soil of mountainous districts or others bare of vegetation, where there is little herbage and much earth or rock, may be very pleasant and wholesome. But citing such cases is only evading the question. It does not follow that water draining off cultivated fields or dense jungle, or flowing between banks covered with luxuriant and rank vegetation, will be equally harmless. Putrefying animal matter is very offensive, but putrefying green vegetable matter, though not so disgusting in idea, is scarcely less offensive. Nor, be it remembered, are the poisonous properties very much dependent or connected with a disgusting taste or smell, and the most powerful poisons come from the vegetable kingdom.

In my first communication, the oxidising action of the atmospheric air dissolved in river water was brought forward as a powerful agency for purifying the water. And though Dr. Frankland's results were quoted as strikingly illustrating it in respect to the Thames waters, yet such observations are by no means new. And it must again be observed that the high temperature of the climate will materially assist this action. No doubt it assists putrefaction, fermentation also, and in some cases this may take place in a river, when its course from any cause is rendered very slow. But in the case of the Hooghly the tides cannot fail to act beneficially; twice every day damming back the water and again retreating, enabling the river to flow with increased velocity, increasing the motion amongst its waters and constantly changing the surfaces exposed to the air. This is just one of those agencies that escape general observation: it does not exhibit itself to the senses, yet it must be remembered that it is by the oxygen dissolved by water, small though that be in amount, that animal life is preserved in the waters no less than in the ordinary atmosphere.

The organic matter remaining in the mother liquors, after having as well as practicable crystallised out or otherwise removed the mineral saline constituents, is, in the case of the hot season river water, of a pale brownish yellow colour, with a comparatively faint, somewhat urinous smell; that from the tanks and river water of the rains is of a darker brown colour and a more excrementitious smell: a smell, in fact, similar to that of Guana. So far as sensible properties go, the latter is the more disagreeable, and according to the results of experiment mentioned in the first paper, probably at least equally nitrogenised. At present it would be difficult to speak more positively on the subject.

In my first paper, and more particularly in the abstract of it furnished for the proceedings of the Society, I made some remarks in connection with some of the tanks which my own observations will not bear out. This was the result of haste and inadvertence, which

will now be corrected. Some of the best tanks, General's Tank more particularly, are probably equal to the river water in purity at some seasons, and superior to it at others. Tank water deteriorates during the hot season from putrefactive fermentation; the river water proper improves from oxidation, but near Calcutta deteriorates from sewerage and tidal water. Tank water improves during the rains by dilution with rain water, and the animal and vegetable life in it preserves the proper balance, removes decaying matters, and prevents putrefaction to any great extent at least, this is the case in good tanks. General's Tank seems a well kept aquarium; it abounds in animal life: though its water has often a slightly putrid flavour, this is easily removed by exposure. But even the water of that tank is not, in my opinion, equal in freedom from organic impurity to the river water proper, taken during the dry season at ebb tide.

General Conclusions.

Before closing this communication, it may be well to make a few general remarks as to the conclusions to be drawn from the data obtained. It must have been observed that there is some uncertainty connected with the subject of the organic matter. Persevering enquiry may in time enable us to remove much of this uncertainty, but at present we can only draw conclusions from the most certain grounds we possess. Probably all will agree that it is advisable to get

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