790 EXPERIMENT STATION RECORD. [Vol.41 



set of commercial bituminous road materials, it was found that comparatively 

 few materials whose penetration at 25° could not be ascertained required more 

 than 30 minutes for a test with the new instrument. Most of the material pre- 

 pared for hot-surface treatment showed a test of less than 15 minutes. 



Progress reported on wood-block experiments in Minneapolis, C. H. Tees- 

 dale and J. D, MacLean {Engin. Netcs-Rec, 82 {1919), No. 5, pp. 233, 234, fiff- 

 1). — The results of an investigation made on an experimental wood block pave- 

 ment after 12 years' service under heavy traffic conditions are reported. The 

 purpose was to study the relative merits of various species of wood for paving 

 material and to investigate the influence of (1) heartwood and sapwood, (2) 

 length of blocks, and (3) angle of courses. Seven species of wood were em- 

 ployed — including tamarack, Norway pine, long-leaf pine, white birch, Douglas 

 fir, western larch, and hemlock. The long-leaf pine was used as a basis for 

 comparison. 



It was found that the order of efficiency of service was as follows: (1) Long- 

 leaf pine, (2) white birch, (3) eastern hemlock, (4) tamarack, (5) Norway 

 pine, and (6) western larch. The depressions and wear of Douglas fir were 

 from two to three times as much as those of the long-leaf pine portion laid at 

 the same time. For most of the species the depressions were very slight dur- 

 ing the first four or five years' service. After this period the depressions in- 

 creased at a very rapid rate. Certain sections showed wearing qualities of Nor- 

 way pine which compared favorably with those of long-leaf pine and white 

 birch. The western larch sections had the greatest percentage of area affected 

 by depression. This was also one of the species which showed the heaviest wear. 

 The order of the species, beginning with that showing the least wear, was as 

 follows : White birch, long-leaf pine, Norway pine, tamarack, eastern hemlock, 

 and western larch. 



The presence of sapwood did not seem to be an important factor affecting 

 the durability of the pavement. The various lengths of blocks employed had no 

 apparent influence on the wearing qualities of the pavement. Less joint wear 

 was noted in sections laid at 45 and 67i° than iu the section of blocks laid at 

 an angle of 90° with the curb. 



Distribution of pressures through earth fills, A. T. Goldbeck {Anwr. Soc. 

 Testing Materials Proc, 17 (1917), pp. 640-661, figs. 9).— The object of this 

 investigation was to obtain data on the distribution of vertical pressures 

 through earth fills under concentrated loads, with particular reference to the 

 design of highway structures. Sand fills were investigated up to a depth of 5 

 ft. and the pressures under them measured with a special diaphragm cell. The 

 principles of pressure measurement with the use of this instrument depend 

 upon (1) the equilibration of the soil pressure with air pressure within a small 

 cell buried where the pressure is desired, (2) the detection of the instant of 

 equilibration by the breaking of electrical contact within the cell, and (3) the 

 measurement of the air pressure within the cell at the instant of equilibration 

 by the use of a sensitive gauge. 



The cost of farming with a tractor (Farm MaeJiinery, No. 1446-1447 {1919), 

 pp. 25, 26, 84, 86, 88, figs. 3). — This is a report in detail of a 310-hour run of 

 a tractor in harvesting 127 acres of wheat, thrashing the grain, disking 34.5 

 acres of land, and plowing all of it. This test is considered to simulate a 

 season's work for the tractor. 



The total cost per acre for fuel and oil in harvesting was 14.5 cts., for 

 thrashing 14.32 cts., for disking 10.84 cts., and for plowing 47.06 cts. Out of the 

 total operating time of 310 hours and 9 minutes, 7.2 per cent was lost on ac- 

 count of implement trouble and 3 per cent on account of tractor trouble. It was 

 found that the tractor was better than horses for opening up a field of wheat for 



