EXPERIMENTS WITH MIXED GRADES. 



177 



hand diagram of figure 60. In the right-hand 

 diagram the curve for discharge 0.363 ft. 3 /sec. 

 is repeated, and with it are placed the corre- 

 sponding curves for four of the component 

 grades that for grade (F) being omitted 

 because it is nearly coincident with the one for 

 grade (E). 



The curve for the mixture is not only of the 

 same type with the others, but runs nearly 

 parallel with those nearest. For all slopes the 

 capacities obtained for the mixture are greater 

 than for any component. The fact that the 

 mixture gives a greater capacity than does the 

 fine grade (C) alone shows that the addition to 

 (C) of 35 per cent of (D) and 20 per cent of 



still coarser grades works an advantage instead 

 of a detriment. 



In figure 58 it is seen that the addition of 20 

 per cent of coarser d6bris to grade (B) in- 

 creases capacity, and in figure 59 that a 

 similar increase accompanies the addition of 

 20 per cent of coarser debris to grade (C). 

 So far as the case of the more complex mixture 

 is comparable to these, there is no indication 

 that a mixture of great complexity has ad- 

 vantage for traction over a mixture of two 

 components only. As to this point the in- 

 ference from data of the five-part mixture is 

 supported by that already drawn from a 

 datum of the (A,C t G 2 ) mixture, and it is 



300- 



200- 



200 



O 



ra 



Q- 



co 



u 



100 



Slope 



fG> - 



.4- .8 1.2 



Discharge 



FIGURE 01. Capacity-slope curves for related mixtures and capacity-discharge curves for mixture and component grades. 



further supported by the facts brought to- 

 gether in the left-hand diagram of figure 61, 

 which shows the capacity-slope curves of mix- 

 tures (C 4 E t ) and (C 4 GJ along with that for the 

 five-part mixture. 



The right-hand diagram of figure 61 is a 

 group of plots of capacity as a function of dis- 

 charge. These plots pertain to the complex 

 mixture and its five components, and all are 

 conditioned by a slope of 1.2 per cent. They 

 show that the fractional superiority of the 

 mixture is not confined to the use of a particu- 

 lar discharge, and they indicate also that the 

 capacity-discharge relation is essentially the 

 same for the mixture as for separate grades. 

 The locus of C =f(Q) for the mixture is approxi- 

 mately a straight line, and if produced it inter- 

 sects the axis of Q to the right of the origin. 

 It might be expressed by an equation in the 

 form of (64) with an exponent near unity. 



20021 No. 8014 12 



A NATURAL GRADE. 



Two series of experiments were made with an 

 alluvium in its natural condition, except that 

 the very finest constituents had been removed 

 by passing it over a 60-mesh sieve. The obser- 

 vations are recorded in Table 4 (K), and the 

 adjusted capacities in Table 60. In figure 62 

 the capacity-slope curves are plotted, and each 

 is accompanied, for comparison, by the corre- 

 sponding curves for grades (A) and (C). 



The approximate mechanical analysis of this 

 material, stated in terms of the separated 

 grades of tho laboratory series, is as follows: 



Per cent. 



(A) 

 (B) 

 (C) 



13 



27 



Per cent. 



(D) 42 



(E) 10 



Coarser than (E) 2 



The fact that the capacities (fig. 62) are 

 greater than those for grade (C), notwithstand- 

 ing the dominance of a component correspond- 



