EXPERIMENTS WITH MIXED GRADES. 



173 



Each vertical column of capacities shows the 

 tractional power of the current, first for the 

 finer component alone, then for mixtures with 

 progressively increasing shares of the coarser 

 component, and finally for the coarser alone. 

 The order of the different groups is that of the 

 contrast in fineness between the finer and 

 coarser components. If the linear fineness of 

 the finer be divided, in each case, by the fine- 

 ness of the coarser, the ratios obtained are 

 (AG) (CG) (BF) (CE) (EG) 

 16.2 9.7 8.5 3.4 2.9 



CA)' 



(G) 



(E) 



(G) 





 100 



50 

 50 



100 

 



FIGURE 55. Tractional capacity for mixed debris, in relation to propor- 

 tions of component grades. 



The data of the table are plotted, with a 

 different arrangement, in figures 55 and 56. 

 In figure 55 the total capacities are plotted in 

 relation to the proportions of fine and coarse 

 in the mixtures. The vertical scale being of 

 capacity, the horizontal, if read from right to 

 left, is of percentage of the finer component, 

 or if read from left to right, is of percentage of 

 the coarser. Figure 56 (p. 1 74) shows, in parallel 

 columns, the capacities for the component 

 grades, those for the coarser components being 

 at the left. 



Attention may first be directed to the total 

 capacity curves of figure 55. If the capacities 



for mixtures were related in the simplest 

 manner to the proportions of components, the 

 curve of capacities would be a straight line 

 joining the points (at the extreme left and 

 extreme right) given by the capacities for the 

 components. The (EG) curve that placed 

 lowest in the diagram lying wholly above such 

 a hypothetic line, would suggest that all mix- 

 tures give an advantage in traction, but this 

 suggestion is not supported by the other 

 curves. The upper curve, for example, would 

 lie as much below as above a straight line 

 joining its extremities. The capacity for the 

 mixture appears always to exceed what may 

 be called the pro rata estimate when the finer 

 component has the higher proportion, but it 

 may fall below that estimate when the coarser 

 component predominates. 



The curves of figure 56 show the capacities 

 apportioned to the components of the mix- 

 tures. Each one represents that portion of 

 the total load which consists of the material 

 of one component. In each curve of the left- 

 hand column the ordinate at the right repre- 

 sents the load of the coarser material when by 

 itself, and the successive ordinates toward the 

 left show how the load is modified by the 

 admixture, in the material fed to the current, 

 of gradually increasing percentages of the 

 finer debris. There are no observations with 

 very small percentages of the finer material, 

 but in each case the second fixed point of the 

 curve shows an increase of load. The addition 

 of the finer d6bris not only increases the total 

 capacity but increases the capacity for the 

 coarser d6bris. The amount of the latter 

 increase appears to be greater as the contrast 

 in fineness of components is greater, and in 

 the extreme case the capacity for the coarser 

 is multiplied by 3.5. The capacity of the 

 current for debris of grade (G) is 16 gm./sec.; 

 but when that debris is mixed with twice its 

 weight of grade (A), which is 16.2 times as 

 fine, the capacity for the mixture is so large 

 that one-third of it, apportioned to grade (G), 

 is 56 gm./sec. In three of the five suites of 

 experiments the highest capacity recorded for 

 the coarser debris corresponds to the mixture 

 of 1 : 1 . In the others it corresponds approxi- 

 mately to 2:1 and 1:2. If the position of the 

 maximum is related to contrast in fineness, it 

 is associated with a larger ratio of the finer 

 component when the contrast is great. 



