592 EXPERIMENT STATION RECORD. [Vol.38 



Disinfection of water by means of bleaching powder, H. Langeu {Ztsvhr. 

 Uyg. u. Infelctiomkrank, 81 {1916), p. 296; Chein. Ztg., 41 {1911), Repert., p. 

 166; (lbs. in Jour. Soc. Chcm. Indus., 36 (1917), No. 13, p. 733).— A distinction 

 is drawn between disinfection, i. e.. rendering bacteria liarmless, and the 

 killing of bacteria. In the case of bleaching powder, disinfection is dependent 

 only upon the concentration of the available chlorin, not upon the duration of 

 the exposure, "iie action is a rapid one and does not consist in oxidation but 

 in absorption of elilorin. The time required to kill the bacteria depends only 

 upon their power of resistance to the injury effected by the chlorin. Disinfec- 

 tion, therefore, is independent of the time elapsing before neutralization of the 

 chlorin. AVhether this follows at a longer or shorter interval, the killing of 

 the bacteria is not influenced. The presence of organic matter reduces the 

 concentration of the available chlorin, though the amount of this reduction 

 can only be determined by a bacteriological test. The disinfecting action is 

 rendered greater by adding the bleaching powder in fractions, a cumulative 

 effect replacing that of concentration. 



The interaction of chlorid of lime with the normal constituents of natural 

 waters and sewage, G. W. Heise (Philippine Jour. Sci., Sect. A, 12 (1917), 

 No. 1, pp. 17-35, figs. 5). — Studies of the rate of decomposition of chlorid of 

 lime in water, sewage, and solutions of organic substances are reported. 



It was found that " in the dark, at 28° C, the reactions proceeded with 

 almost constant velocity for periods of 30 minutes to one hour, after which 

 they proceeded very slowly. In the light the decomposition rate was greatly 

 accelerated. In general, the amount of available chlorin consumed is propor- 

 tional to the con-centration in which it is added, as shown by the Interaction of 

 chlorid of lime and urea solution. However, for certain definite concentra- 

 tions of sewage this regularity fails. A study of the reaction between chlorid 

 of lime with varying quantities of urea showed that the chlorin consumption, 

 as measured by the starch-potassium iodid reaction, is not necessarily propor- 

 tional to the concentration of organic matter. The determination of the 

 chlorin consumption of a water or sewage, though of importance in the con- 

 trol of hypochlorite disinfection, is not sufficient in itself and should be sup- 

 plemented by bacteriological tests." 



The construction and operation of concrete septic tanks, H. C. CvitPBELi. 

 (Doin. Engin.. 80 (1917), No. IS, pp. 488-^90, figs. 2),— Notes are given on resi- 

 dential sewage disposal by means of small septic tanks and tile absorption 

 areas. 



Practical road building-, C. E. Foote (Philadelphia: David McKay, 1917, pp. 

 XX+11-295, figs. 40). — This is a popular treatise on the subject for the beueflt 

 of the layman, containing chapters on road history, location, grades, drainage, 

 foundations, surfaces, bridges and culverts, traffic and finance, and on earth, 

 gravel, sand clay, topsoil, macadam, brick, concrete, bituminous, sand asphalt, 

 and special surface roads. 



Serial bonds for road building save money, M. O. Bldridge (Engin. Newa- 

 Rec, 79 (1917), No. 9, pp. 407-411, figs. 5). — Tabular and graphic data are re- 

 ported and discussed from which the conclusion is drawn that on the basis of 

 definite comparisons between the ultimate costs of different types of bonds for 

 road building the serial type is the most desirable. " Especially in local road- 

 improvement work, where the sinking funds lead to many troubles, serial 

 bonds are greatly to be preferred. . . . 



" Bond issues ought to be resorted to only where they can not be avoided. It 

 should be a fundamental rule in the financial operations of a county or town- 

 ship that all current expenses, such as for the maintenance of roads, be paid 

 from the proceeds of an annual tax levy. Furthermore, if a township or 



