and chemical analysis fail to detect anything unusual in its character, is it not a fair presumption that such water is wholesome, and good water for the use of a town supply?-The question is whether it can be always and permanently so used. That seems to me to be the real point at issue. We should have found out long ago the injurious effects even of small quantities of sewage if the sewage were always injurious; but that is not asserted. It is only supposed that under certain exceptional conditions, even sewage may become very injurious. The injurious character of a water impregnated with sewage matter might not be discovered for years. You might go on using it for years, and it might not be discovered; and yet you might have some outbreak of disease in the place, which nevertheless might be connected with the use of that sewage

water,'

Following the evidence of Sir Benjamin Brodie came that of the late Dr. Miller and Dr. Angus Smith. From this it is not necessary to quote, but it will be sufficient to observe that these gentlemen supported to a considerable extent the views of Dr. Frankland relative to the nitric acid in water.

The Commissioners themselves make the following observations in reference to the self-purification of streams:

'But though for these reasons we believe that the organic contamination of the Thames is much less than is commonly imagined, still it would be sufficient to do great mischief, were it not for a most beneficial provision of Nature for effecting spontaneously the purification of the streams. Some of the noxious matter is removed by fish and other animal life, and a further quantity is absorbed by the growth of aquatic vegetation; but in addition to these abstractions, important changes are effected by chemical action. The organic compounds dissolved in the water appear to be of a very unstable constitution and to be very easily decomposed, the great agent in this decomposition being oxygen, and the process being considerably hastened by the motion of the water. Now, as such water always contains naturally much air dissolved in it, the decomposing agent is ready at hand to exert its influence the moment the matter is received into the water; in addition to which the motion causes a further action by the exposure to the atmosphere: and while (as in the Thames) the water falls frequently over weirs, passes through locks, &c., causing further agitation and aeration, the process must go on more speedily and more effectually.

'The effects of the action of oxygen on these organic matters when complete is to break them up, to destroy all their peculiar organic constitution, and to rearrange their elements into permanent inorganic forms, innocuous, and free from any deleterious quality.'

On this pleasing picture we would now offer a few comments.

First, with regard to the removal of some of the noxious matters by fish and vegetables, we would remark, that during their life they perform execretory functions, giving up to the water, products, the nature and properties of some of which are not well ascertained, and

the imbibition of which by human beings is not altogether a pleasant subject to contemplate. Again, it must be remembered, that the time arrives when these animals and vegetables die, and aid in the corruption of the water; there is always in every river a vast quantity of decaying vegetable, and not a little animal, matter.

Secondly. Although the oxidising process above described does in time effect the destruction of certain forms and kinds of organic matter, no evidence has yet been obtained showing that it really does destroy the materies morbi of cholera, typhoid, and other epidemic and contagious diseases, and of which it has been found that water is a frequent distributor.

Thirdly. Neither has it been proved that the action of oxygen is to convert, even in those cases in which changes are really effected, all the organic substances into permanent inorganic forms, innoxious and free from any deleterious quality;' in fact, the usual effect of the transformation is to convert one series of organic compounds into another of a different nature.

Fourthly. The important fact is overlooked that the apparent purification is in part due, not to chemical transformation at all, but to precipitation. It is in this way that the faecal and much other suspended matter is removed from running water; it falls to the bottom of the river, fouling the bed, and in its turn polluting the water.

We will now make a few further remarks as to the significance to be attached to the presence of the nitrogenous organic matter, ammonia, and nitric acid found in water. These are in themselves in no respect injurious except when contained in water in very considerable amount; waters are met with which contain but small quantities of such substances, and yet have been productive of disease; on the other hand, waters are in use largely contaminated with such compounds, and which have yet not been known to produce disease. The interest which attaches to the nitrogenous organic matter, the nitric acid, &c., of water, and the reason for determining the quantities in which these are present, lies in the fact taught by experience, that, as a rule, to which there are many exceptions, waters which abound in those substances are those which most frequently give rise to disease; but the purest distilled water would do the same thing if in any way it were to become contaminated with the infectious or contagious matter of typhoid fever: and hence the public ought obstinately to refuse to drink water, and especially river water, polluted with sewage, and this although they are assured it has been filtered after the manner usually practised by water companies.

The next point to which we would advert is the interpretation to be put on the presence of nitrates and nitrites in water. Dr. Frankland affirms that they are derived from the oxidation of various kinds of nitrogenous matter proceeding from several different sources, and that their amount indicates the extent of the contamination to which the waters containing them have been, at some time or other, subjected.

Dr. Odling dissents from these views, and thinks there may be other sources of the nitrates and nitrites, but does not indicate a single additional source, while the facts adverted to in reply to question 6462 rather confirm than otherwise Dr. Frankland's views as to the source and origin of those oxidized nitrogenous compounds. It is only when Dr. Frankland bases his estimate of the previous sewage contamination on the quantity of nitrogen thus found that he seems to be at fault; but even here the fault is rather in the opposite direction to that indicated by the objectors to Dr. Frankland's views. Thus in waters containing much vegetation, part of the nitric and nitrous acids, as well as of the undecomposed nitrogenous matter, are absorbed, and so disappear, and are lost to analysis and subsequent calculation.

The late Dr. Miller, like Dr. Odling and one or two other witnesses, expressed the opinion that the nitric acid found in water might be derived from other sources than decaying organic matter, vegetable or animal, in air or water; but Dr. Miller, like other witnesses, failed to indicate any other source than that mentioned, and we believe we may take it as an established fact, so far as relates to the waters in domestic use in this country, that the nitric acid contained in them is invariably derived from organic matter of some kind or other, and it is for this position that Dr. Frankland has so long and ably contended.

Nitric acid in water is, then, really to be regarded as the representative of decayed organic matter; or, as Dr. Frankland somewhat figuratively denominates it, as the skeleton of sewage, and as the evidence, and to some extent the measure, of previous sewage contamination. But this being so, it does not follow that every water containing it, even in large amounts, is to be condemned; on the contrary, supposing the nitric acid to be unaccompanied by nitrogenous matter, and further, supposing the water not to be liable to ready contamination by such matter-as, for example, the waters of the deep wells of Kent -then we may safely presume such water to be safe for use, even for drinking purposes; although this water is too hard to be the type of really the best and most suitable water for domestic use. When, however, a water contains any considerable amount of uitric acid, and at the same time any great amount of nitrogenous organic matter, or, if even free from such matter, is placed under such circumstances as to render it liable to such contamination, then the water should be condemned and avoided.

To the above observations of our own may be added some of the criticisms of the Commissioners relative to the inferences based upon chemical analyses made for them, and especially the conclusions of Dr. Frankland, to which we have already referred at such length.

The Commissioners specially object to the term 'original sewage contamination,' and to the statement that the quantity of nitrites and nitrates found represent the measure of the previous sewage contaminations. They remark that Dr. Frankland refers the origin of the nitrites and nitrates not simply to organic matter taken generally,

D

THE ANALYSIS OF TEA.

&

It has already been stated that the chief constituents of tea consist of chlorophylle, gum, glucose, gluten, cellulose, tannin, theine, volatile oil and mineral matter.

For the purpose of estimating the soluble constituents of tea, the leaves must be thoroughly exhausted by boiling with repeated quantities of distilled water until the infusion is no longer coloured and ceases to yield on evaporation any solid residue. The different infusions thus obtained are mixed together and reduced by evaporation to a certain bulk. One portion is evaporated with magnesia to dryness on the water bath, the magnesia being used to neutralise the tannic acid and to set the theine free; and in this the theine is estimated in the manner to be hereafter described.

Another quantity of the infusion is mixed with spirits of wine, to precipitate the gum, while a third quantity is taken for the estimation of the tannin.

The insoluble portion of the leaves is dried and weighed ; the difference in the weight as compared with the original quantity taken gives the proportion of the constituents soluble in water.

For the determination of the nitrogenous matter, sometimes termed Legumin, a separate portion of tea must be taken, and a combustion analysis for nitrogen made, the amount of nitrogen present in the theine being deducted from the total amount obtained. The remaining nitrogen, multiplied by 6:33, gives the proportion of nitrogenous matter or gluten.

The usual soda-lime process does not furnish the whole amount of nitrogen, since the theine yields, on heating with alkalies, some cyanide, which of course would not be obtained as ammonia. The oxide of copper combustion, although exact, involves a very great deal of trouble and labour. We give the following outlines of the process :

0-2 to 0.5 gramme of tea are mixed intimately with recently ignited oxide of copper. A combustion tube, drawn out in the usual way, is first charged for the length of 4 inches with a mixture of bicarbonate of soda and of bichromate of potash, then with a few inches of pure oxide of copper, then with the mixture containing the tea, then with another layer of pure oxide of copper, and lastly with a spiral of metallic copper. The air contained in the tube is first driven out by heating the layer of bicarbonate of soda, and thus generating carbonic acid. The gases produced by the combustion of the tea-mixture are collected over mercury, freed from carbonic acid by means of caustic-potash solution, and the nitrogen is measured, attention of course being paid to the temperature, pressure of the air, and the moisture of the gas; for all of which circumstances tables have been specially prepared.

For the estimation of the water and the ash a separate portion

a

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must be taken; the tea should be dried on a water bath; the loss represents the water; the residue is incinerated and the ash weighed.

For the estimation of the volatile oil a considerable quantity of tea must be operated upon. This must be distilled with water and the distillate received into a cool receiver; the oil should be found floating on the surface of the water. We may state, however, that, in certain attempts we have made, we have failed to obtain any weighable amount of the oil; the distillate had the odour of tea, but no oil drops were visible. Such is a brief outline of the processes to be adopted in the analysis of tea. The estimation of the sugar and chlorophylle are exceedingly difficult, the tannin decomposing into sugar and gallic acid, and hence reducing the copper solution in the same manner as sugar. They are seldom if ever required, and therefore it is unnecessary to give any details respecting their determination. To resume,

For the infusion from which the theine, gum and tannin are to be estimated take five grammes of tea; for the combustion half a gramme, and for the estimation of water and ash three grammes.

Of the infusion of the five grammes reduced to a bulk of 500 cc., 300 cc. are used for the estimation of the theine, 100 cc. for thegum, and the last 100 cc. for the tannin.

The estimation of the Theine.—The theine may be conveniently and simply estimated by Mulder's process, which is thus carried out: The 300 cc. of the solution are to be evaporated, with the addition of some magnesia, to dryness ; the residue is then finely powdered and transferred to a flask, capable of holding about 200 cc. ; 30 cc. of ether are poured over it, and allowed to digest for two days, with occasional shaking. The ether is then heated to boiling and poured into a small weighed flask. The residue is heated two or three times with successive quantities of ether, until this on evaporation ceases to furnish any crystalline deposit of theine. These several quantities are added to the first quantity of ether employed, and the whole is evaporated on the water-bath to dryness. The theine is left in a crystalline condition, and is then weighed together with the flask.

The difficulty of the solubility of theine in ether has suggested to Mr. Otto Hehner a modification of this process. In this absolute alcohol is used as a solvent, theine being much more soluble in this menstruum. The alcohol by boiling extracts not only all the theine, but a small quantity of other substances which are to be thus removed. The alcoholic solution is evaporated on the water bath to a few drops and ether is added; this precipitates the foreign substances, but does not now throw down the theine, since it is already in a state of solution. The ethereal solution is evaporated and the theine in the manner described above. Of course, it is necessary to thoroughly exhaust the extractive matter by treatment with two or three successive quantities of alcohol.

Another method, but one involving more time and trouble, is the following, as proposed by Péligot. The tea is exhausted with boiling