CLAYS OF NEW YOEK 



541 



niuneric expression of it by testing the tensile strength of the air- 

 dried clay. 



The same opinion was held by two Kussian investigators, "W. 

 Aleksiejew and P. A. Cremiatschenski/ who hold that plasticity 

 is not only due to the interlocking of the clay particles, but varies 

 also with the fineness of the grains, the extreme coarse' and extreme 

 fine ones having inferior plasticity. 



In this country Wheeler's work on the Missouri clays has sub- 

 stantiated these views.^ Experiments by the writer on the clays of 

 Korth Carolina, Alabama, ISTew York and other states incline, him 

 toward the idea that there may be much in this theory. It 

 seems very probable that the true explanation will be obtained by 

 combining Cook's and Olchewsky's theory. 



Interlocking of the grains no doubt has much to do with the 

 tenacity exhibited by highly plastic clays, but the gliding of the 

 particles is probably explained by the circumstance that such 

 movement offers the least resistance to surface tension. 



Tensile strength, however, seems to be more affected by size' of 

 grain than plasticity is. Fine-grained clays seldom show high 

 tensile strength, whereas some fine-grained clays show high plas- 

 ticity. That a certain relation appears to exist between plasticity 

 and tensile strength, and that the former does not necessarily in- 

 crease with the amount of kaolinite (or indirectly alumina) pres- 

 ent are shown by the following tests of some ISTorth Carolina 

 clays. 



Tensile strength in 

 pounds per sq. )ii. 

 Per cent of 

 alumina Average Maximum 



Roanoke Rapids plastic clay . . . ; 16 . 09 206 218 



Washed kaolin 40 . 61 20 22 



Spoutsprings fijie-grained clay 32.51 24 29 



While this relation between tensile strength and plasticity seems 

 to hold good in a large majority of clays, still it can not be said 



' Zap. imp. rvs.<<k. techn. obschtsch, 1896. 80, pt 6-7. 

 * Missouri genl. sur. 1897. 11: 10'^. 



