1917] KUKAL ENGINEEEING. 787 



and the sand and clay, when thoroughly mixed, should he sufficient to fill the 

 voids between the larger gravel particles." 



An appendix on typical specifications is included. 



Earth roads and the oiling of roads, H. A. LaRue (Univ. Missouri Bui., Ill 

 (1916), No. 16, pp. 29, figs. iO).— This bulletin deals with the construction, 

 grading, and maintenance of earth roads, and with the history and general con- 

 siderations as to oiling roads and selection of road oils, and with methods of 

 oiling earth, macadam, and gravel roads. The principal items in the proper 

 oiling of earth roads are summarized as the " proper drainage of both surface 

 and subsurface, heavy grading done at least one season in advance of oiling, 

 proper shaping of the roadway to form a good crown and gutters, maintenance 

 of the surface with the road drag for some time previous to oiling to insure 

 compact and smooth roadway, carefail removal of dust before oiling (this is 

 of the utmost importance), proper method of applying oil (includes thorough 

 mixing of oil in earth), use of the right kind of oil (quality of oil can be de- 

 termined only by proper tests), and proper maintenance after oiling and re- 

 newed oiling as needed." 



Width of wag'on. tires recommended for loads of varying magnitudes on 

 earth and gravel roads, B. B. McCoemick (V. S. Dept. Agr., Office Sec. Circ. 

 12 (1911), pp. 6, figs. 6). — "The recommendations in this circular relating to 

 widths of wagon tires suitable for use on country roads of earth and gravel, 

 as well as upon those of a more improved type, are based upon two factors, 



(1) the unit weight for width of tire commonly used for road rollers, and 



(2) the results secured from a large series of traction tests conducted by the 

 Office of Public Roads and Rural Engineering, extending over several years 

 and made in widely scattered localities throughout the United States. . . . 



" From the curves shown the following conclusions may be drawn for well- 

 constructed dry earth roads: With a gross load of 5,000 lbs. the unit draft 

 decreases with the width of tire up to and including the 5-in. width. The 

 unit draft decreases directly as the weight per inch width of tire decreases, 

 until a weight of 2-50 lbs. per inch of tire is reached. . . . The fact that the 

 draft for a 6-in. tire is larger than that for a 5-in., in all cases shown, merely 

 indicates that there is no advantage in increasing the width of tire beyond a 

 certain point, and there may be a disadvantage in so doing. It is not advisable 

 to exceed in any vehicle a unit weight per inch of width of tire in excess of 

 that possessed by a standard road roller. 



" While there has been in the past, and to a certain extent still is to-day, 

 wide variation in sizes and types of wagons marketed by the different manu- 

 facturers, it is believed that five sizes of wagons will be sufficient to meet all 

 the needs of farming operations and all general work except the heaviest 

 trucking and certain specialized hauling, which is likely to be confined to city 

 pavements. These five sizes are (1) a one-horse wagon having a gross load 

 capacity of 2,000 lbs. and a skein from 2 J to 2| in., (2) light two-horse wagon 

 A\-ith a skein approximately 2i in. and a gross carrying capacity of 3,500 lbs., 



(3) medium two-horse wagon with a skein not exceeding 3 in. and designed 

 for a gross load of 4,500 lbs., (4) standard two-horse wagon with a skein of 

 3f in. and a gross carrying capacity of 6,800 lbs,, and (5) heavy two-horse 

 wagon having a skein of 3^ in. and gross load capacity of 7,.500 lbs." The 

 widths of tire recommended for these five sizes of wagon are respectively 

 2, 2*, 3, 4, and 5 in. '"'■^^ 



"As there is considerable differ^ce in the practice of manufacturers regard- 

 ing the size of skein used on the various types of wagons, it is recommended 

 that wagons be not designated by size of skein but according to the gross load 

 94087°— No. 8—17 7 



