1920] RURAL ENGINEERING. 889 



port. Miss., December 18. li)19, in which an experiment on clearing 25 acres of 

 cut-over l()iif,^leuf pine land and the destructive distillation of stumps is re- 

 ported. Tallies of data and cost analyses are al.so included. 



The tract selected was of fairly average condition and the stumps ranged 

 from 6 to 15 years in age. The stumps were removed with dynamite at a total 

 cost per acre varying from $22.14 to $41.39. While the average of these figures 

 is not considered a true indication of the average cost of clearing such lands in 

 general, it is noted that the cost per ton of wood recovered was lowest on the 

 land costing the most to clear. It is aLso noted that in shooting longleaf pine 

 stumps the character of the soil did not vitally affect the cost because the 

 charge of explosive was confined within the root. 



A small-sized horizontal retort was used for the distillation. The products 

 of distillation of these stumps were charcoal, tar, and so-called mixed tar oils. 

 The cost of equipment and construction was .*i;4 ()4(5.S2. Considering total oper- 

 ating costs, interest, depreciation, repairs, supplies, and labor, and profit per acre 

 on a 24-hour operating schedule was $12.33 and on a 36-hour schedule $12.81. 



While the plant used proved to be slightly too small, it is concluded that 

 destructive distillation offers great possibilities for anyone who contemplates 

 clearing longleaf pine lands on a fairly large scale. "Generally speaking, a 

 man would hardly employ the distillation process on less than 1,000 acres, 

 even though ... it might be possibe to make a profit by using 500 acres, and 

 doubling the depreciation figures." 



E.xperiments on the horizontal pressure of sand, P. M. Crosthwaite 

 {Surveyor and Mittiic. and Count}/ Engin., 57 {1920), No. 11/66, p. 182). — This is 

 a review of a report, presented before the Institution of Civil Engineers, de- 

 .scribing experiments the results of which led to the conclusion that the vvedge 

 theory, when modified by leaving out wall friction and introducing instead of 

 the angle of repose the angle of internal friction, gives correct results in all 

 cases whether for the maximum thrust or that produced by individual wedges. 



Test of bearing capacity of rock at Iron Canyon dam site, Calif., H. J. 

 Gauxt {Reclam. Rec. [U. S.], 11 {1920), No. 8, pp. 37S, 379, fig. i).— These tests 

 indicated that the softest rock on the site could stand a pressure of nearly 

 40 tons per square foot without yielding. The material is mainly agglomerate. 

 It is considered safe to design a dam with pressure on this foundation not to 

 exceed 10 tons per square foot. The testing apparatus is de.<?cribed and 

 illustrated. 



How to use cement for concrete construction for town and farm, TI. C. 

 Campbell {Chicago: Stanton <£■ Van Vliet Co., 1920, pp. [l]+380, figs. 214).— 

 This is a popular treatise on how to build concrete structures for town and 

 farm and includes formulas, drawings, and tabular data. Special sections are 

 included on the proportioning, mixing, and laying of concrete and on form 

 construction. 



California highways, B. Blow {San Francisco: Author, 1920, pp. XVIII -{- 

 S08, pis. 187. figs. 2.j). — This is a descriptive record of road development by the 

 State of California and by such counties as have paved highways. It is pro- 

 fusely illustrated. 



First biennial report of the Kansas Highway Commission {Kans. High- 

 uag Comn. liien. Rpt., 1 {1917-18), pp. 276, pis. 18. figs. 4). — ^This is the first 

 biermial report of the Kansas State Highway Commission, which Includes a 

 short r^sumg of road and bridge building and legislation pertaining thereto up 

 to the time a State highway commis.sion was establishe<l, together with data on 

 the work and expenditures on roads and bridges in the State for the period from 

 April 4, 1917, to January 1. 1919. A .special section describes tests of road 

 building materials as conducted at the Kansas State Agricultural College. 



