THE ANALYST. 443 PARLIAMENTARY REPORTS. METHODS OF TREATING AND DISPOSING OF SEWAGE. FIFTH REPORT OF THE ROYAL COMNISSION ON SEWAGE TREATMENT. (Cd. 4278.) THE Commission wag appointed to inquire and report (la) what method or methods of treating and disposing of sewage (including any liquids from any factory or manu- facturing process) may properly be adopted, consistently with due regard for the requirements of the existing law, for the protection of public health, and for the economical and efficient discharge of the duties of local authorities ; ( I b ) if more than one method may be so adopted, by what rules, in relation to the nature or volume of the sewage, or the population to be served, or other varying circumstances or require- ments, the particular method of treatment or disposal to be adopted be determined;444 THE ANALYST.(2) to make any recommendations which may be deemed advisable with reference to the treatment and disposal of sewage. The first Report issued (1901) by the Commission was of an interim character, and dealt with the suitability of different lands or soils for the purification of sewage ; the second Report (1902) was a formal document covering certain scientific papers which were presented as an Appendix to that Report; in the third Report (1903) the Commission dealt with the relations between local authorities and manufacturers in regard to the disposal of manufacturing effluents. The Commissioners found that the present state of the law was most unsatisfactory, that the attitude of local authorities towards manufacturers had differed widely, and that many manufacturers were seriously handicapped ; purification of the effluents by the local authorities is in the great majority of cases practicable, and could be done more cheaply than by the manufacturers themselves.Recommendations covering these points are then made. The fourth Report (1904) deals with the pollution of tidal waters, with special reference to the contamination of shell-fish, The present Report deals chiefly with the relative merits of the various methods which are available for the purification of the sewage of towns. The Commissioners are satisfied that it is practicable to purify the sewage of towns to any degree required, either by land treatment or by artificial filters, and that there is no essential difference between the two processes; the choice of a scheme must depend on a number of considerations which are discussed helow.I t is generally desirable to remove from the sewage, by a preliminary process, a considerable proportion of the grit and suspended matters, before attempting to purify it on land or by means of filters ; two or three hours’ quiescence is usually sufficient to produce a tank-liquor fairly free from suspended solids, whilst, in the case of continuous flow sedimentation, the period of flow should generally be from ten to fifteen hours. Only about 25 per cent. of the organic solids present in domestic sewage are digested in the septic tank, when the tanks are worked at a twenty-four hours’ rate; the liquor issuing is bacteriologically almost as impure as the sewage entering the tanks, and is not more easily oxidised in its passage through filters than is domestic sewage which has been subjected to chemical precipitation or simple sedimentation.NO definite rules can be laid down as to how long a septic tank should be run with- out cleaning, and the rate of flow through the tank is a matter which requires special consideration for each place. At but few places should the sewage be allowed to take longer than twenty-four hours or less than twelve hours to flow through the tank, and at least two tanks should be provided, so that, if necessary, one tank can be used a k m . There is less risk of nuisance if the tank and the feed channels to the filters are covered in. The addition of from 2 to 3 grains of lime per gallon considerably reduces the amount of suspended solids in the liquor, enables a larger quantity of the liquor to be treated per cubic yard of filter, and the offensive character of the liquor is largely destroyed.I n the case of sewages which contain certain trade wastes, and strong sewages from water-closet towns, it is generally desirable to subject the sewage to some form of chemical treatment before attempting to oxidise the organic matter contained in it. This treatment aids the deposition of the suspended solids and facilitates the aubse-THE ANALYST. 445 quent filtration. With continuous flow, an eight hours’ rate is usually sufficient to produce a fairly good tank liquor from domestic sewage of average strength ; if the sewage is allowed to remain quiescent in the tank two hours’ settlement would usually sufice.Unless special circumstances favour a particular plan, it would appear that there is very little difference in annual cost between the various methods of tank treatment when taken in conjunction with the cost of subsequent filtration. Within ordinary limits, the depth of a contact bed makes practically no diEer- ence to its efficiency per cubic yard, but it is generally inadvisable to construct a contact bed of a greater depth than 6 feet or of a less depth than 2 feet 6 inches. For practical purposes, a given quantity of coarse material will give the same amount of purification whether it is arranged in the form of a deep or a shallow percolating filter, provided that the supply of liquor per square yard is the same.In the case of fine material, it appears that shallow filters have a greater efficiency than deep filters. The amount of sewage which can be purified per square yard of contact bed or of percolating filter varies nearly inversely as the strength of the liquor treated. Taking into account the gradual loss of capacity of contact beds, a cubic yard of material arranged in the form of a percolating filter will generally treat about twice as much tank liquor as a cubic yard of material in a contact bed. Percolating filters are better adapted to variations in flow, yield more aerated effluents, and give less risk of nuisance from smell than do contact beds. There is no essential difference between effluents from land and effluents from artificially constructed filters.Soils which are particularly well adapted for the purification of sewage yield effluents containing only a very small quantity of unoxidised organic matter, and of a higher class than effluents from artificial filters ; unsuitable soils, however, may give very impure effluents. All trade effluents of which the Commission have had experience interfere with or retard processes of purification to some extent, but in no case does the admixture of trade refuse make it impracticable to purify the sewage, although in some cases preliminary treatment may be necessary. As regards the choice of a method of sewage treatment, it is considered that this should depend primarily on local conditions. If a sufficient quantity of good land, to which the sewage can gravitate, can be purchased for about 3100 per acre, land treatment would usually be the cheapest method to adopt.Where only clay land is available, it would be cheaper and more satisfactory to provide artificial filters. Or, if the case were one in which it was necessary to obtain a high-class effluent, it might be cheaper to pay a somewhat higher price per acre than $100, rather than to adopt artificial treatment, or the latter, as usually carried out, yields distinctly inferior effluents. On good land the sewage can be treated at the rate of 30,000 gallons per acre per day; filters with a top layer of very fine material, such as sand, can be made to give good results with a rate of filtration of 400, or even 500, gallons per cubic yard per day, if the sewage be weak and well clarified.No general rule can be laid down as to the increase in flow, due to storms, which should occur in branch sewers before sewage is allowed to pass away by the overflow untreated; the general principle should be to prevent such an amount of unpurified sewage from passing over the overflow as would cause a nuisance. Under446 THE ANALYST. the arrangements recommended by the Commission (stand-by tanks, sufficient filter area, etc.), no storm sewage arriving at the outfall works would be discharged without some preliminary method of settlement, The Commission further recommend that a Central Authority should determine the nature of tests which are to be applied for the purpose of standards, and that it should be made the duty of the Rivers Board or of the County Council to determine from time to time, subject to appeal to the Central Authority, what standards should be adopted.In the first instance, it would be convenient that the Central Authority should prescribe one standard for all non-tidal waters; in place of the existing statutory provisions, and that the Rivers Board or County Council should fix a higher or lower standard where required. If an effluent, complying with the standard fixed for the water into which it is discharged, gives rise to a complaint, no action should be allowed to be brought in respect of alleged damage; but the Central Authority, on ascertaining that the complaint is well founded, should be empowered to fix a different standard.Should an effluent not comply with the statutory standard, actions for damages should be brought in the ordinary Courts. Power should be conferred on the Central Authority to suspend the operation of any standard to allow time for the construction of works, etc. For the guidance of local authorities, it is provisionally stated that an effluent would generally be satisfactory if it complied with the following conditions : 1. That it should not contain more than 3 parts per 100,000 of suspended matter; and 2. That, after being filtered through filter-paper, it should not absorb more than : (a) 0.5 part by weight per 100,000 of dissolved or atmospheric oxygen in twenty- four hours. ( b ) 1.0 part by weight per 100,000 of dissolved or atmospheric oxygen in forty- eight hours; or (c) 1.5 parts by weight per 100,000 of dissolved or atmospheric oxygen in five days.Apart from the question of drinking-waters, there is no evidence that the mere presence of organisms of a noxious character in a river constitutes a danger to public health or destroys the amenities of the river. Generally speaking, therefore, there is no justification for demanding that a, local authority shall so treat its sewage as to render it bacteriologically pure ; the cost would be practically prohibitive. Storm- water as well as sewage would have to be treated, and the water of rivers would still require to be treated before it could be distributed for drinking purposes. The Central Administrative Authority would be empowered to secure the economical and efficient discharge of the duties of local authorities and others, in regard to pollution, and to protect public health, as the conditions of different cases vary to such an extent that the necessary control cannot be provided by any direct enactment which could be enforced by the ordinary Courts.The Central Authority would also deal with (1) disputes between local authorities and manufacturers as to the terms and conditions on which the trade effluents shall be admitted to the sewers ; (2) the control of shell-fish layings ; (3) the protection of water-supplies from pollution ; (4) the collection of information as to the available water-supplies of the country;THE ANALYST. 447 ( 5 ) the collection of information as to the need of water in various parts of the country ; (6) the settlement of standards for different reaches of water ; (7) conferring powers on local authorities to provide separate sewers for surface water and to enforce the provision of separate drains; and (8) the settlement of questions as to the extra, amount of sewage which a local authority should be required to treat during storms.The Report also gives the results of a number of experiments carried out with the object of ascertaining the manurial value of sewage sludges. A record of these investigations is published as an Appendix (No. 8) to the Report. Dr. W. Somerville, as the general result of his experiments, concludes that the nitrogen and phosphoric acid of sludge are in a much less available form than the same substances in sulphate of ammonia, superphosphate, and fish-meal.None of the sludges experimented with produced any considient manurial effect on the growth of turnips, swedes, or mangolds. Professor T. H. Middleton states that the figures obtained do not permit of any conclusions as to the relative values of sludge and artificial manures. The only definite conclusion is that, in the case of root crops and grass, the action of the nitrogenous and phosphatic constituents of sludge is very slow as compared with the effect pro- duced by nitrogen and phosphates supplied by ordinary artificial manures. Dr. J. A. Voelcker concludes that further experiments are necessary before the effect of sludge on grass-land can be determined; the only clear benefit wag to be traced to the more quickly acting material sulphate of ammonia, and it is by no means certain that permanent improvement of the pasture resulted.I n the case of wheat, the experiments showed that the different sewage sludges used, when employed in sufficient quantity to supply 40 pounds of nitrogen per acre, were capable of increasing the yield of both corn and straw by 10 to 12 per cent. above the unmanured produce. The ‘‘ artificial equivalents ” of the different sludges produced an increase in corn and straw of 16 to 17 per cent. above the unmanured produce. The tendency of the use of sewage sludges is to produce a greater length of straw. From a practical point of view, none of the sludges used would be worth 10s. a ton on the farm for wheat- growing purposes. These investigations show that, on the whole, the manurial constituents of sewage sludge act much more slowly than those of ordinary artificial manures.w. P. s. THIRTY-SECOND ANNUAL REPORT OF H.M. INSPECTORS OF EXPLOSIVES, 1907, 17-18. Tests for Mercury in Explosives. F. H. AND P. V. DUPR~. For the detection of mercury, different classes of explosives require different treatment, and in some cases very delicate methods are necessary to detect the minute quantities present. I n all cases a special form of spectrum-tube has been employed by the authors. This consists of two stoppered tubes of about 20 C.C. capacity joined by a capillary tube. One of the stoppers carries a, tube fitted with a tap; all grinding must be very carefully performed, in order to hold a vacuum for448 THE ANALYST.several hours. About the centre of each tube, the electrodes, contained in tubulures slanted up so as to prevent the entrance of the explosive, are attached. The parts of the tubes below these tubulures are filled with the substance to be examined, the stoppers are replaced, and the apparatus is exhausted by a vacuum pump (not a mercury pump). The parts of the tube containing the explosive are immersed in water at 90" C., and a discharge from a 6-inch induction coil is passed through. The capillary tube is then examined, end on, preferably with the aid of a condenser to increase the brilliancy of the spectrum. If traces of mercury be present its spectrum will be seen, together with those of any other gases, such as oxygen, hydrogen, nitrogen. The spectrum of nitrogen may be eliminated by passing a current of hydrogen through the cold tube before exhaustion.The lines which are relied on for proving the presence of mercury are : yellow, 5,790 and 5,769 ; green, 5,461 ; violet, 4,359. Ungelatinised guncotton may be tested directly ; gelatinised explosives may be prepared by grinding with French chalk. In the case of cordite and hard gelatinised explosives, the mercury salt is extracted by ether and separated by electrolysis under conditions fully described in the Report. Minute traces of metallic mercury are detected by concentrating its vapours on silver-foil by heating the explosive with the foil in a closed bottle. Small traces of mercury may enter an explosive in the form of contamination by means of machinery previously used with mercury salts.Cases are on record where traces of mercury persisted in the products for six months after the use of mercury salts had been discontinued. The authors have ascertained that -001 mgm. of mercury is sufficient to retard the heat test of an explosive by five minutes. The use of a strip of silver-foil in carrying out the heat test counteracts the effect of the mercury, but itself has a masking action on the test owing to the absorption of the acid vapours by the silver. Gold is less objectionable than silver, but is quite inadmissible with nitroglycerin explosives. Heat Test Papers for Explosives.-Several batches of paper tried by the authors, though otherwise satisfactory for the heat test of explosives, have been found to contain Home substance, insoluble in water, which is capable of liberating iodine from potassium iodide in the presence of acetic acid. I n future all papers prepared for this test should be washed twice, for half an hour each time, in a 10 per cent. solution of acetic acid, and subsequently washed for at least twelve hours in a running stream of tap-water. After two rinsea in distilled water and drying, the paper is ready for dipping. The authors point out the necessity of adhering most closely to the specified details in carrying out the heat test, as small variations may cause great discrepancies. Papers may be checked against approved papers prepared by the authors. Amongst variations in carrying out this test the authors have encountered : variations in the method of heating the bath, interference with the convection currents, insuflicient grinding, excessive moistening of the papers, e tic. J. F. B.