490 EXPERIMENT STATION RECORD. I Vol. 88 



dilution could always be used, the results would be of some comparative value. 

 The biological oxygen consumption of any sewage as determined by this method, 

 however, could not be balanced against the oxygen in a stream, since almost 

 any value could be obtained for the sewage, depending upon the dilution 

 used. . . . 



" As a practical test, the English method of determining biological oxygen 

 consumption is subject to very grave errors and is only applicable under limited 

 conditions. These conditions are that the same dilution must always be used if 

 results are to be at all comparable and that incubation must extend over at 

 least three days at 20°. Oxygen demand for longer periods may then be cal- 

 culated by Phelps's formula." 



Bacteriological study of sewage purification by aeration, R. Russell and 

 E. Babtow (Univ. III. Bui., I4 {1916), No. 5, pp. S48-358). — Investigations on 

 the bacteriology of sewage purification by aeration brought out the following 

 features : 



" There is a large and consistent reduction of the total number of bacteria 

 in the sewage. The actual stabilization process is due to a typical aerobic 

 bacterial flora which gains almost complete ascendency. The other inhabitants 

 are largely incidental. The actual nitrification is accomplished by two typical 

 known nitrifiers, nitrosomonas and nitrobacter." 



Purification of sewage by aeration in the presence of activated sludge, 

 E. Babtoav and F, W. Mohlman (Univ. III. Bui., 14 (1916), No. 5, pp. 325-335, 

 figs. 5).' — Some further experiments on this process are described (E. S. R., 34, 

 p. 591). 



Handbook of clearing and grubbing: Methods and cost, H. P. Gillette 

 (New York: Clark Book Co., Inc., 1917, pp. [Vn+241, figs. 67).— In this hand- 

 book are compiled a large amount of data on methods and costs of clearing 

 land, much of which consists of the results of the author's broad experience 

 along these lines. The first two chapters deal with factors affecting cost esti- 

 mating and appraising and with specifications relating to methods of land 

 clearing for roads, reservoirs, and railways and for general purposes. Other 

 chapters deal in detail with land clearing practice in general; grubbing by 

 hand ; burning and charpitting ; blasting ; hand, horse, and power stump pullers ; 

 and heavy plows. A list of manufacturers of supplies and equipment for use 

 in clearing and grubbing is included. 



Tests of a large-sized reinforced-concrete slab subjected to eccentric con- 

 centrated loads, A. T. GoLDBECK and H. S. Paibbank (U. S. Dept. Agr., Jour. 

 Agr. Research, 11 (1917), No. 10, pp. 505-520, figs. 11). — In continuation of 

 work previously noted (E. S. R., 33, p. 487; 35, p. 290; 36, p. 788; 38, p. 289) 

 tests on the effect of eccentricity of loading of a reinforced concrete slab 32 

 by 16 ft., 14 in. thick with 13 in. effective thickness, are reported. The con- 

 crete was a 1:2:4 mixture, and the slab which was built in place was sup- 

 ported by concrete abutments. 



It was found that " to provide against the frequently realized condition of a 

 heavy concentrated load applied near the parapet . . . the resisting moment 

 required in the portion of a bridge slab near the outer edges is greater than 

 that which is necessary in the central portion. Further than this, if the rela- 

 tion indicated above be verified and shown to include other span lengths, it 

 would seem that in designing a slab the necessary allowance for the con- 

 centrated load near the outer edge can be made very simple in the following 

 manner: (1) Use the formulas for narrow rectangular beams, subsituting for 

 the breadth (b) the value obtained from the table for central concentrated 

 loads [E. S. R., 35, p. 291] ; (2) determine the loss in effective width due to 



