892 EXPERIMENT STATION RECORD. [Vol. 38 



into as thorough contact with either the sand grains or the brick. The ' dry- 

 layer ' is, tlierefore, weaker than the underlying concrete, and the bond to the 

 brick i.s not great. ... 



" The monolithic tyT>e of construction combines the strength of the brick 

 slab with that of the concrete base in such a manner as to develop the maxi- 

 mum in both, and these tests show that such a compound slab is fully equal in 

 strength to a concrete road slab of the same thickness. It appears, therefore, 

 that in the monolithic brick road the brick and the concrete should not be con- 

 sidered as separate units of a pavement, but rather as integral parts of a single 

 structure. . . . With this type of construction it seems, therefore, en- 

 tirely logical to reduce the total thickness of the slab, either by reducing the 

 thickness of the base or by using thinner bricks, provided a sufficient gross 

 thickness is retained to furnish strength enough to carry the probable loads, 

 and this necessary gross thickness can be determined on the same basis as the 

 thickness of a concrete road." 



Tests on nailed joints in fir and hemlock timbers, H. F. Blood and H. E. 

 Plummer (Abs. in Engin. News-Rec, 79 (1917), No. 19, pp. 871, 872, fig>i. 3; 

 West. Engin., 8 (1917), No. 12, pp. 478-483, figs. 8).— Tests on the strength of 

 nailed joints, using Douglas fir and western hemlock, are reported, which 

 covered 110 joints, 87 with Douglas fir and 23 with western hemlock. All tests 

 were designe<l to show the strength of nailed joints with wire nails used in 

 single shear. 



Safe values for nails driven in perpetidicularly to the grain in either wood, 

 with the load perpendicular to the length of the nail, were established as 

 follows: 10 and 12-penny nail.s, 120 lbs. load value per nail; 16-penny nail. 160 

 lbs.; 20-penny nail, 200 lbs.; 30-penny rniil, 270 lbs.; 40-penny nail, 320 lbs.; 

 50-penny nail, 400 lbs. ; 60-penny nail. 480 lbs. 



** For nails driven parallel with the g^ain of the wood the figures above should 

 be reduced 25 per cent. All of these values should be reduced if the penetration 

 of the nail in the holding piece is less than 50 per cent of its length. 



" Other conclusions in the report are that the resistance of nails driven per- 

 pendicularly in the timber with the grain of the wood parallel to the load is 

 but little more than for nails driven similarly with the grain of the wood per- 

 pendicular to the load. It is also indicated that the standard nail heads are 

 of proper proportions, there being no difficulty with the nail head pulling 

 through the outside timber. The strength of the joint seems to be affected but 

 little by the penetration of the nail in the centerpiece if that penetration is 40 

 per cent or more of the length of the nail, but wth less penetration the loads 

 were reduced, and for a penetration of 30 per cent the strength reduction 

 amounted to about 25 per cent. The examination showed that each nail in a 

 joint seemed to support an equal proportion of the load. . . . 



" The resistance of the nailed joint, if depending solely on the resistance of 

 the wood to crushing, varies with the diameter of the nail, other things being 

 •unchanged. On the other hand the resistance of the joint, if depending solely 

 on ftie resistance of the nail to bending, varies as the cube of the diameter 

 of the nail. As the resistance of the joint depends on the combination of these 

 two, various sized nails give varying degrees of resistance, but it is found 

 that the variation of the resistance corresponds quite closely with the square 

 of the diameter of the nail." 



Relative resistance of various hardwoods to injection with creosote, C. H. 

 Teesdaij: and J. D. MacLean (U. S. Ucpt. Agr. Bui. 606 {1918), pp. 36. pis. 

 12, figs. 16). — Creosote penetration tests similar to those previously reported 

 for coniferous woods (E. S. R., 31, p. 743) are here reported for some of the 



