AUGUST 8, 1902.] 



SCIENCE. 



227 



every drop of water is needed for general irri- 

 gation. In sections of our country not 

 adapted to farming and where land is scarce, 

 the purification of sewage by intermittent fil- 

 tration, which requires only about one twen- 

 tieth the land, has been resorted to, and we 

 are indebted to the splendid experiments made 

 by the Massachusetts State Board of Health, 

 at Lawrence, for much valuable information 

 concerning the efficiency of this system, and 

 which indeed has been adopted by a large num- 

 ber of municipalities both at home and abroad. 

 In communities where land is so scarce that 

 even intermittent filtration is impracticable, 

 a number of processes for the purification of 

 sewage before its discharge into the rivers 

 have been proposed, such as chemical precipi- 

 tation, sterilization, sedimentation, etc. These 

 processes, however, are now considered as 

 wrong in principle and aiming at the unat- 

 tainable, and wherever irrigation or intermit- 

 tent filtration cannot be advantageously car- 

 ried out, preference should be given to the 

 'septic or bacterial tank.' This system was 

 devised by Mr. Cameron, of Exeter, England, 

 and is really an elaboration of the old cesspool ; 

 the tanks are built of concrete, brick or 

 masonry walls, tightly covered to exclude both 

 light and air, and large enough to contain the 

 flow of sewage from 1,500 to 2,000 persons for 

 from twelve to twenty-four hoiirs. The raw 

 sewage without screening or any preliminary 

 treatment enters by two inlets which are car- 

 ried down five feet below the surface in order 

 that the entry may be quiet, so as not to dis- 

 turb the bacterial layers, also that air may 

 not be carried in or any gases escape back to 

 the sewer. After passing through a 'grit 

 chamber' 10 feet deep by 7 feet long and 18 

 feet wide, the sewage flows over a wall sub- 

 merged one foot below the surface into the 

 main portion of the tank, which is 65 feet in 

 length, 7 feet 6 inches in depth and 18 feet 

 wide, its capacity- being 53,800 gallons, or ap- 

 proximately a day's supply; hence the transit 

 of the sewage is ordinarily very gradual, aver- 

 aging about 24 hours in the tank, so as to give 

 ample time and quiet for the putrefactive 

 changes which are brought about by the an- 

 aerobic bacteria, and which result in the di- 



gestion of the siispended organic matter, or 

 its conversion into simpler, soluble forms and 

 gases. The effluent from the tanl^, brownish- 

 yellow in color and offensive in odor, after 

 being aerated by being run over a weir and 

 cascade arrangement, is next passed over the 

 'Dibdin bacteria beds' filled with coke breeze 

 and clinkers, where the nitrifying organisms 

 perform their share of the work, until the fil- 

 trate is fit to be discharged into the water 

 courses, although whenever practicable it 

 should be previously passed through well- 

 drained land or over water meadows. 



The advantage of the tank lies in the re- 

 duction in the amount of suspended matter; 

 the accumulation of sludge from the sewage 

 and excreta of 1,500 persons amounted to but 

 four feet at the end of three years' trial; the 

 operating expenses are also very slight and so 

 far the bacterial or septic tank has given the 

 most satisfactory results from a sanitary and 

 economic standpoint, where broad irrigation 

 or sewage farming cannot be applied. Chap- 

 ter 12 deals with the agricultural value of 

 bacterial effluents and conservation of the val- 

 uable constituents of sewage, the classification 

 of trade effluents and the recovery of waste 

 products. George M. Kober. 



Georgetown Univeesitt. 



SCIBXTIFW JOURNALS AND ARTICLES. 

 The third (July) number of Volume 3 of 

 the Transactions of the American Mathemat- 

 ical Society contains the following papers : 

 ' On the Group defined for any given Field by 

 the Multiplication Table of any given Finite 

 Group,' by L. E. Dickson; "Nachtrag zum Ar- 

 tikel : ' Zur Erklarung der Bogenlange, u. s. 

 w.,' " by O. Stolz ; ' Proof of the Sufficiency 

 of Jacobi's Condition for a Permanent Sign 

 of the Second Variation in the so-called Iso- 

 perimetric Problems,' by O. Bolza ; ' On Hy- 

 percomplex Number Systems,' by H. E. 

 Ilawkes ; ' On Metabelian Groups,' by W. B. 

 Fite ; ' Conjugate Rectilinear Congruences,' by 

 L. P. Eisenhart ; ' Constructive Theory of the 

 Unicursal Cubic by Synthetic Methods,' by D. 

 N. Lehmer ; ' The Groups of Steiner in Prob- 

 lems of Contact (second paper),' by L. E. Dick- 



