RURAL ENGINEERING. 889 



The results are taken to indicate " (1) that, apart from the use of slurry 

 from percolating filters, the initial production of activated sludge can be facili- 

 tated and obtained with considerably less air cost than originally was the case, 

 (2) that under certain controlled conditions the volume of air required maj- be 

 considerably less than previously estimated, and (3) that there is an economic 

 advantage in employing an increased volume of activated sludge with special 

 reference to the rate of nitrification." It is concluded " that the estimated 

 costs of aeration indicate that the activated sludge method of sewage purifica- 

 tion is eminently a practical process." 



Experiments to determine the economic possibilities of sludge from. 

 Emscher or Travis tanks, A. Y. De Lapoete {Ann. Rpt. Prov. Bd. Health On- 

 tario, 33 (1914), pp- 139-141, fiff. 1). — Experiments are reported, the results of 

 which to date are taken to indicate that "(1) the sludge has practically no 

 value as a fertilizer or a fuel, (2) extraction for the recovery of the grease 

 or distillation with superheated steam would not pay, and (3) destructive 

 distillation designed to recover the grease, gas, ammonia, etc., might cover 

 expenses." 



Tables facilitate accuj.'acy in tim.ber beam, design, R. C. Hakdman (Engin. 

 Rec, 73 (1916), No. 5, pp. 138, 139).— The errors in the usual practice of timber 

 beam design based on nominal sizes are pointed out, it being stated that 

 deficiencies in sizes of timbers vary from i to f in. Factors to be applied to 

 tables of safe loads and a table of actual sizes, sectional areas, and section 

 moduli for commercial lumber surfaced on one side and one edge are given. 



Influence of temperature on the strength of concrete, A. B. McDaniei. 

 {Univ. III. Engin. Expt. Sta. Bid. 81 {1915), pp. 24, figs. 15; abs. in Engin. and 

 Contract., 44 {1915), No. 21, pp. 405-408, figs. 7). — Experiments on the influence 

 of temperature on the attainment of strength in concrete are reported. These 

 included three groups of tests, namely, 45 6- by 6-in. cylinders, 51 6-in. cubes, 

 and 60 8- by 16-in. cylinders. The concrete was composed of 1 part cement, 

 2 parts sand, and 4 parts broken stone, by weight, corresponding to 1 part 

 cement, 2.2 parts sand, and 3.6 parts broken stone, by volume. The test 

 specimens were stored in temperatures varying from 26.5 to 95.6° F. The 

 temperature of storage was determined by daily readings of the maximum and 

 minimum thermometers. The following conclusions are considered justifiable : 



" Under uniform temperature conditions, there was an increase of strength 

 with age within the limits of the tests. For any temperature the rate of 

 increase decreases with the age of the specimen, and this rate of increase is 

 less correspondingly at the lower temperature conditions. For the specimens 

 tested, under normal hardening temperature conditions of from 60 to 70°, the 

 compressive strength of the concrete subjected to a uniform temperature at 

 the ages of 7, 14, and 21 days may be taken as approximately 50, 75, and 90 

 per cent of the sti*ength at 28 days, respectively. For lower temperatures the 

 percentage values are less, and for higher temperatures the percentages are 

 higher. The relation between the percentage values at the ages of 7, 14, 21, 

 and 28 days is nearly the same for temperature conditions from 30 to 70°. 

 However, the values for the lower temperatures should be used with caution. 

 Concrete which is maintained at a temperature of from 60 to 70° will at the 

 age of one week have practically double the strength of the same material 

 which is kept at a temperature of from 32 to 40°." 



Curves of the results are also presented for convenient use. 



Use of water-gas tar and coal tar on concrete subjected to high, velocities of 

 water, C. H. Paul {Reclam. Rec. [V. S.], 7 {1916), No. 1, p. 46; Engin. and 

 Contract., 40 {1916), No. 3, p. 56). — The use of water-gas tar and coal tar on the 

 concrete surfaces of the regulating outlets through the Arrowrock dam is 



