Febeuaky 6, 1903.] 



SCIENCE. 



213 



parts where the shock is absorbed in pro- 

 ducing deformation. The effect of low 

 temperatures, for instance, is to elevate 

 the elastic limit of steel, i. e., to convert it, 

 from the mechanical standpoint, into a 

 harder steel ; and when a bar that is pai-tly 

 frozen is broken in tension the frozen sec- 

 tion suffers but little deformation iinder 

 impact, while the other segments are 

 stretched to the point of plasticity. 



In case of harder steels, the indications 

 are not so evident. It is difficult to obtain 

 two bars east from the same heat of steel 

 that are of the same grain, and comparisons 

 of individual bars are apt to be misleading. 

 In general it may be said tliat the ductility 

 under impact of hard steels may fall below 

 that under gradual tests depending on in- 

 fluences not understood. There are differ- 

 ences of ductility under impact not de- 

 tected by the gradual test. 



Nicking the surface of a bar renders it 

 less ductile under an impact test than un- 

 der a gradual test. The shape of the cross- 

 section and condition of surface have a 

 minor influence. In the case of both 

 hard and soft steels the ductility is greater 

 when the bar is broken by a number of 

 blows than when broken with one blow. 

 "Within ordinary limits the speed of de- 

 livery of a given amount of energy at one 

 blow has no appreciable effect on the ductil- 

 ity. Low temperatures decrease the ductil- 

 ity more decidedly under impact than un- 

 der gradual loading. 



Cementation of Road Material and Elastic- 

 ity of Clays: Allerton S. Cusiiman, 

 Bryn Mawr College, Brjni Mawr, Pa. 

 The method of testing the binding or 

 cementing power of road materials was 

 briefly described. It was pointed out that 

 the cementing value was a phenomenon of 

 the same nature as the plasticity of clays. 

 Results obtained in the road material lab- 

 oratorj" of the Department of Agricultiu'e, 



seem to point to the fact that plasticity is 

 dependent on a colloid condition of the 

 particles. No sample has ever been met 

 with that exhibited plasticity that did not 

 contain water of combination, although 

 many samples which contain water of com- 

 bination do not exhibit plasticity. Only 

 one sort of water of combination (the so- 

 called Micellian water of Nageli and Van 

 Bemmelen) is in any way a measure of 

 plasticity. The inorganic colloids or so- 

 called 'hydrogels' have been studied by 

 Van Bemmelen. They are chiefly char- 

 acterized by the peculiar structural rela- 

 tion they bear to water. They can be 

 hydrated and rehydrated indefinitely un- 

 less by heating to too high a temperature 

 the colloid structure is destroyed. Ex- 

 actly the same phenomenon characterizes 

 plastic clays and rock powders. The sur- 

 faces of roads are continually being pow- 

 dered by the effect of traffic wear and 

 weathering, and the particles are contin- 

 ually being cemented and recemented. If 

 the material of the road lack plasticity 

 the particles blow and wash away too 

 rapidly. The binding quality of such 

 rocks as limestones and dolomites is a func- 

 tion of the hydrogel impurities present 

 usually either in the form of silicic acid or 

 hydrated oxide of iron. 



Topographical Work, V. S. Geological Sur- 

 vey: H. M. Wilson, "Washington, D. C. 

 A verbal description of recent topo- 

 graphic work done by the U. S. Geological 

 Survey, the extent of the same as far as 

 completed being shown upon a map of the 

 United States. 



TUESDAY EVENING, DECEMBER 30. 



Construction of Washington Monument 

 and Library of Congress: Bernard R. 

 Green, "Washington, D. C. 

 A description of the construction of the 



