RELATION OF TENSILE STRENGTH TO FINENESS OF GRAIN.
Curves were plotted from data given by Ries', and also by Beyer and Williams', showing the relation between fineness of grain, as delineated by the surface factor, and tensile strength. There did not appear to be any consistent relation between these two factors, shown by the curves.
ball clay. This clay is so fine by itself that it is extremely difficult to dry without air checking, but with increasing adulteration of sand up to 30 per cent by weight, the tensile strength increased up to a maxi mum in the sample where the sand was of extreme fineness, and here again the tensile strength decreased rapidly. This drop in the curve is credited to the inability of the extremely fine mixture to part with its mechanical water without checking, thus causing flaws in the briquette and very materially weakening it. In this experiment we have at both extremes very fine grained materials; one a pure ball clay and the other the same ball clay adulterated by fifty per cent by weight of a very fine sand, both having a low tensile strength. The intermediate members of this series show increasing strength with decrease of size of grain. So far at least as this one case is concerned, increase in size of grain increases tensile strength. Fineness of grain and tensile strength are, therefore, functions of one another.
We know that a fine-grained shale is, in a majority of cases, im proved by adulteration with sandstone, even in the fact of the fact that the sandstone is very coarse. At Streator, Ill., there are two strata of shale in one bank, the one, being very gritty, is easily manufactured into a good paver; the other, a close grained plastic shale, gives trouble in every stage of manufacture, and makes a poor paver. Yet these
two shales are said to be of very similar chemical composition. The writer believes that the cause of this difference does not lie in their chemical composition. shrinkage, or ability to slake easily, but in their drying behavior. Judging from the results of Prof. Orton's experi ment on the tough ball clay, it is believed that if many of the plastic, fine grained clays were by addition of coarse material opened suffi ciently to permit ready egress of the mechanical water, they would be excellent paving brick material', while without such a treatment they would be worthless for anything other than building brick, simply be cause the bond of the clay would be weakened in drying by the expand ing steam inside of the brick which could not readily escape.
In Fig. 14 data are plotted showing the relation between fineness of grain and tensile strength. This is indicated by the dotted line.
It will be noted that there is a general relation between fineness of grain and tensile strength. This is indicated by the dotted line.
There is a remarkable coincidence in the relative positions of the several clays in Fig. 14 and Fig. 11. The same relative positions of the several clays is to be seen also in Fig. 12 which shows the relation be tween volume shrinkage and surface factor. This same relative posi tion of the clays, one with another, was developed also when the rela tion between the sum of the excess and hygroscopic water and the surface factor, and also the relation between the sum of the excess and hygro scopic water and the tensile strength, were plotted. In the last two in stances, however, the order in which the clays occurred was the reverse of that in Fig. 14 and 11.