For instance, Mr. Fowler, the chemist in charge of the Manchester experiments, observed before the Royal Commission on Sewage Disposal as follows: “It is a delicate operation (the management of septic tank and contact beds), which requires careful watching! There is no doubt whatever about that!” (Question 5651.) Again, the conditions of successful working of contact beds, laid down by the same gentleman on page 64 of the Manchester report for the year ending March 27, 1901, are ample proof of this, and they show very clearly how extremely careful the supervision of such a plant ought to be, and that in the hands of inexperienced men it will soon come to grief. Professor Percy Frankland stated in his evidence before the Royal Commission, that in his opinion land required less skilled supervision than contact beds. (See Questions 9937, 10071-74.) A similar view was expressed by Mr. H. M. Wilson, the chief inspector of the West Riding of Yorkshire Rivers Board. (Question 6380.) VII. SOME OBSERVATIONS ON THE DEPOSITION OF SUSPENDED MATTERS IN TANKS. [Sidenote: Definition of the term “deposition.”] The term “deposition” shall here be held to mean the precipitation of the suspended matters without chemicals or other artificial means, i.e. the unaided subsidence of these matters at such a rate of flow that septic action is not set up within the tanks. The question that is of interest here, is: Which is the most favourable rate of flow of the sewage through the tank, so far as the deposition of the suspended matters is concerned? To some extent the answer to this question will depend on the special characteristics of the particular sewage under consideration, but for general purposes the following observations will not be without interest. Although of very great importance, this question does not appear to have received very general consideration, as the available number of careful experiments is but small. [Sidenote: Tank velocity at Barking.] It appears that the calculated velocity in the channels of the precipitation tanks at Barking is about 4 feet per minute, and that with this velocity about 77 per cent. of the suspended matters were deposited in the year 1894. [Sidenote: Tank velocity at Manchester.] At the Manchester tanks it is stated that a velocity of 3 feet 4 inches per minute is employed. [Sidenote: Velocity frequently adopted.] A rate of velocity now frequently adopted in this country for new works is 6 inches per minute. [Sidenote: Frankfort experiments.] In the settling tanks at Frankfort on the Main there are deposited about 84 per cent. of the suspended matters, with velocities ranging from 9½ inches to 16½ inches per minute. [Sidenote: Cassel experiments.] With a velocity of 7 inches per minute, it is stated that at the Cassel sewage works 97 per cent. of the suspended matters are retained in the tanks. [Sidenote: Hanover experiments.]