7. Very small weak tops, and of a pale yellow colour; apparently the poorest plot of all.

8. Good strong healthy plants, and very regular in the rows. 9. Plants very regular, and appearance about the same as Plot 4.

A casual observer could readily distinguish the plots upon which nitrogenous manures had been used from the others, by the dark green colour which the potato-tops on these plots presented. On the other hand, he would at once recognise the parts of the field to which potash-salts, and especially common salt, had been applied, by the pale green colour of the tops.

The plots manured with potash-salts did not look very promising at first, but they subsequently recovered and yielded a good increase, although the tops throughout the whole period of growth were paler in colour than on the unmanured portions of the field. On the plot which had received 4 cwts. of salt, in addition to 4 cwts. of superphosphate, the potatoes made no way, looked pale and sickly, and yielded only an inconsiderable increase over the unmanured plots.

For the sake of better comparison the increase of each plot over the average yield of the unmanured portions of the field has been calculated in the following tabular statement:

TABLE XIV. Showing the Increase of each Manured Plot per Acre over the average yield of the Unmanured portions of the Potato-field at Escrick Park Home-farm, 1869.

Average produce of unmanured plots, 6 tons 11 cwts. 68 lbs.

A glance at the preceding table shows:

1. That the greatest increase was obtained by applying to the

potato crop per acre a manure composed of 4 cwts. of mineral superphosphate, 2 cwts. of potash-salts and 2 cwts. of sulphate of ammonia.

This application produced the large crop of 12 tons 5 cwts. and 40 lbs. per acre, and gave an increase of over 5 tons of potatoes over the yield of the unmanured plots.

2. That next to the compound artificial manure used on Plot 1 dung had the most beneficial effect upon the potato crop.

3. That mineral superphosphate and potash-salts, without sulphate of ammonia, yielded much less increase than the same mixture with sulphate of ammonia.

4. That the addition of nitrate of soda to superphosphate and potash-salts had a less beneficial effect than the addition of sulphate of ammonia to the same fertilising agents.

5. That a compound artificial manure, suited to the requirements of the crop intended to be raised, and to the character of the soil to which it is to be applied, frequently has a better effect than Peruvian guano.

6. That common salt, applied to potatoes in considerable quantities, rather injures than benefits the crop.

A general review of all the recorded experiments on the potato crop, if I am not mistaken, warrants the conclusion that on light land excellent crops of potatoes may be grown at a comparatively small expense by means of artificial manures, consisting of superphosphate, potash-salts, and sulphate of ammonia, and that on heavy land, in a good agricultural condition, sulphate of ammonia may be omitted from a potato manure, either altogether or in part, and that on such land a small quantity of nitrate of soda, added to superphosphate, generally has a better effect than sulphate of ammonia.

Laboratory, 11, Salisbury Square, Fleet Street, E.C.
July, 1870.

XXII.-On the Composition and Practical Value of Several Samples of Native Guano prepared by the A B C Sewage Process of the Native Guano Company. By DR AUGUSTUS VOELCKER, F.R.S. Of the various plans which have of late been recommended for the purpose of effecting the purification of town sewage, and of extracting from it a dry and portable manure of sufficient fertilizing value to pay the manufacturing expenses, and by the sale of the manure to realise an income leaving a margin for profit, none has attracted so much public attention as

the process which for some time past has been carried out at Leamington, and quite recently at Hastings, by the Native Guano Company.

This Company has adopted Sillar's Patent A B C process in the treatment of town sewage, and professes to extract from it a valuable dry artificial manure, and at the same time to render sewage bright and clear as water, and to remove the impurities from it so efficiently that the clarified sewage, after treatment by the A B C process, may be discharged into a river or watercourse without causing any nuisance in the immediate neighbourhood or locality through which the effluent and purified sewage flows. Messrs. W. C. and R. G. Sillar and W. G. Wagner, in the specification of their patent, describe the A B C process as follows:

"We add to the sewage to be purified a mixture consisting of the following ingredients-alum, blood, clay, magnesia or one of its compounds, by preference the carbonate or the sulphate, manganate of potash, or other compound of manganese, burnt clay, otherwise known as ballast, chloride of sodium, animal charcoal, vegetable charcoal, and magnesian limestone. Of these substances the manganese compounds, the burnt clay, chloride of sodium, and magnesian limestone may be omitted, and it is not essential that both animal and vegetable charcoal should be used. If any of the ingredients named should from any cause be present in sufficient quantity in the sewage, it may, of course, be omitted from the mixture. The proportions in which the ingredients are to be used vary according to the nature of the sewage to be purified, as, for instance, if a large proportion of urine is present, we increase the proportion of clay; if the sewage is much diluted, we slightly increase the proportion of alum and blood; if it contains a large proportion of street refuse we decrease the proportion of clay.

"For ordinary sewage the following preparations have answered well:

"These substances are mixed together and added to the sewage to be purified, until a further addition produces no further precipitate. The quantity required will be about 4 pounds of the

mixture for 1000 gallons of sewage. The sewage must then be thoroughly mixed with the compound and allowed to flow into the settling tanks. The greater part of the organic and other impurities will be immediately separated in the form of large flakes, which rapidly fall to the bottom, leaving the supernatant water clear and inodorous, or nearly so. The matter may then be allowed to accumulate at the bottom of the tank. In some cases it is preferable to add the compound of manganese to the water after the sediment produced by the other ingredients has been allowed to subside. The sediment will be found to possess the power of precipitating a further quantity of sewage; it must therefore be pumped or otherwise taken from the tank and mixed with fresh sewage, the sediment being allowed to subside in the same way as before. The sediment may be used 5 or 6 times in this way. When the sediment no longer possesses the power of precipitating the impurities of sewage, it must be removed from the tank and allowed to dry; when partially dry a small quantity of acid, by preference sulphuric acid, may be mixed with it, which will retain all the ammonia in a soluble form. When dried, the sediment will be a valuable manure."

of

It will be noticed that besides alum (A), blood (B), and clay (C)-ingredients suggestive of the name of the A B C processa large number of other substances are included in the preceding list of chemical agents, which may be employed in the treatment of sewage by the process. The use of alum for the purpose clarifying foul water has been known from time immemorial, and found efficacious in precipitating more or less perfectly the nitrogenous or albumenoid compounds which are present in sewage and similar refuse liquids. Town sewage has always an alkaline reaction, and yields with a weak solution of alum an abundant flocculent precipitate. There is therefore no need to introduce into sewage nitrogenous or albuminous matters in the the shape of blood, with a view of causing a flaky precipitate, which, like coagulated white of eggs, will carry down with it suspended impurities, and thereby effect the clarification of the muddy liquid. The patentees, therefore, are wise in giving only the faintest sprinkling of blood to their precipitating mixture. If they omitted the blood altogether, the manure which they abstract from sewage, other conditions being equal, practically would be neither the worse nor the better for this omission, nor would the purification of the effluent sewage be less complete. Why 10 parts of chloride of sodium should be mentioned as one of the ingredients in the preceding mixture is difficult to comprehend, for, being a very soluble salt it will, of course, pass off with the effluent water, and in the proportion in which it is employed in the purifying mixture the salt cannot

possibly act beneficially upon sewage in virtue of its antiseptic properties.

It is, however, not my purpose in the present communication to make any further remarks on the merits or demerits of the chemical agents recommended by the patentees of the A B C process, nor do I intend to discuss at length how far this process fulfils the high expectations of its originators, and meets the sanitary difficulties which have to be overcome in the disposal of town sewage. Ample information, referring specially to the sanitary aspect of the great sewage question, will be found in the able reports for 1870 of the Rivers Pollution Commission (1868). Suffice it to state here that the Commission, on the strength of numerous experiments, have come to the conclusion that the A B C process fails in purifying sewage to such an extent as to render it admissible into running water.

As far as my own experience entitles me to express an opinion of the efficacy of the A B C process for purifying sewage, I would observe that I agree in the main with, but do not fully concur in, the view of the Rivers Pollution Commissioners. Sewage clarified by the A B C process, or by the plan recommended by Mr. Leek, or Dr. Anderson of Coventry (who both rely mainly on the efficacy of sulphate of alumina as a precipitating and disinfectant agent), or purified by any other equally efficacious process, I am of opinion cannot be rendered sufficiently pure to be admissible into running water when the sewage of a large town and populous district has to be disposed of, and the available running water, comparatively speaking, is too inconsiderable in proportion to the sewage which is poured into it, clear though it may be. But if the sewage of a small town has to be disposed of, and suitable land for irrigation cannot be procured, or only at an immoderate sacrifice of money; and, on the other hand, a good sized river or abundance of running water is near, into which the effluent and clarified sewage may be run, I believe the discharge of such sewage under these circumstances would not create a nuisance.

It is quite true that sewage, however well purified it may be by any known process of precipitation, always contains a good deal of saline mineral matter and obnoxious organic matter in solution, and for these reasons ought not to be poured in large quantities into a shallow watercourse; but if the disinfected and clear sewage of a small town be poured into a large bulk of running water, it will not materially augment the saline and earthy matters naturally present in the water, and the small amount of organic impurities, when brought into contact with the dissolved air of a large bulk of running water, will rapidly become oxydised, and rendered perfectly inodorous and harmless.