Engineering and Contracting . total sample determined. The most Iiarmful of the feldspathic mate-rials, according to the w-riters experience, oc-curs in the form of small pebbles, or even inlarge irregular masses, of an earthy appear-ance, and of a color ranging from light yel-low to dark brown or black. Though easilycrushed, it will generally have more coherencethan the clods of earth or clay in the , the larger pebbles can be separatedby screening the dried sample through the sieve. If pebbles of other material arealso found, the difference in color will permitof a sepa
Engineering and Contracting . total sample determined. The most Iiarmful of the feldspathic mate-rials, according to the w-riters experience, oc-curs in the form of small pebbles, or even inlarge irregular masses, of an earthy appear-ance, and of a color ranging from light yel-low to dark brown or black. Though easilycrushed, it will generally have more coherencethan the clods of earth or clay in the , the larger pebbles can be separatedby screening the dried sample through the sieve. If pebbles of other material arealso found, the difference in color will permitof a separation. The feldspathic materialspassing the No. 10 sieve, together with thesand, clay and silt, will be left with the sand,as a residue after washing out the other ma-terials. Separation of the feldspar can thenbe made in the manner described for this material occurs in greater proportionsthan about 8 per cent of the total sample, bydry weight, the road surface will cut and G3 GO >. 55 a S 50 40 rJ5 :» 3 - 20 15. Dust 10 20 10 60 80 100 Fig. 1. Graphic Analyses of Sand-Clay Road Mixtures Showing Limiting Curves. cases, to make out the characteristic laminatedstructure. The separation of the mica is often a diffi-cult operation. This is especially true ofsoils in which it is present in a finely dividedstate. In washing a sample of such a soil,the mica will go into suspension in the waterwith the clay and silt. If the clay and siltprecipitate before the mica, it is easy to re-move the latter by drawing off the wash-waterand passing it through a paper filter. Other-wise, it would be impossible to effect a sep-aration of these materials. Soils in whichthere is much finely-divided mica wilt usuallypresent a characteristic, lustrous surface. In most cases, however, the mica can bercmovcfl from the sample by washing out theclay and silt carefully (as previously describedunder Separation nf .Sand and Clay), theresidue being sand and mica particles. \ sep-aration of th
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