574 



SCIENCE 



[N. S. Vol. XXXVII. No. 954 



This census was inaugurated by Mr. H. H. 

 Schmidt, chief engineer, and placed under the 

 charge of the writer. 

 PetrograpMc Study of Eochs for Boad-maUng in 



the Office of PuUio Scads: E. C. E. Lord, 



petrographer, U. S. Office of Public Roads, 



Washington, D. C. 



This paper contains a review of a quantitative, 

 microscopic method of rock analysis by means of 

 a cross-line field, and a brief statement of the 

 principal road-making rocks, their method of 

 classification and physical properties. Attention 

 has been called to the effect of mineral composi- 

 tion and rock structure on the wearing properties 

 of road materials. 



It has been shown that the dense, fine-grained, 

 igneous rocks (traps) are generally more tough 

 and offer greater resistance to wear than the 

 coarser grained igneous, or the more loosely tex- 

 tured sedimentary and metamorphie rocks. In 

 consequence of their superior toughness, the 

 screenings from trap rocks are found to be 

 sharper and more wedge-shaped than those from 

 other rock types and therefore produce a more 

 permanent bond when compacted with the larger 

 road stones. 



This interlocking of the coarser portion of the 

 screenings with the rock fragments forming the 

 wearing course of the road constitutes the 

 mechanical bond of the road surface, and should 

 be distinguished from the cementing bond of the 

 fine dust which is due to the presence of adhesive 

 mineral substances of a more or less colloidal char- 

 acter. This cementing value has been found in- 

 sufficient in many cases to withstand the effect of 

 modern traffic and it has therefore been suggested 

 to make use of the highly cementations basic open 

 hearth slag dust to overcome this difficulty. 



Field Methods for Laying Out Sighway Curves: 

 Hene¥ B. Drowne, instructor in highway engi- 

 neering, Columbia University. 

 Read by title. 



The Value of Microscopic Analysis of Bocks to he 

 Used in the Construction of Boads and Pave- 

 ments: J. F. Kemp, professor of geology, 

 Columbia University. 

 Read by title. 



Municipal Plants for the Storage of Boad Oil: 

 William H. Kershaw, chief engineer. Paving 

 and Roads Division, The Texas Company, New 

 York City. 



After comment on the existing conditions re- 

 garding the lack of equipment for storing road 

 oil, with its resulting economic loss, detailed state- 

 ments of the cost of tankcar equipment is given, 

 showing that all extra expense in the handling of 

 road oil that results from lack of proper storage 

 facilities eventually becomes a part of the cost of 

 the oil. Figures given show that 12,000 gallon 

 tanks can be erected at an approximate completed 

 cost of $700. A statement is made that the saving 

 of the accumulating demurrage now charged by 

 tlie railroads will pay for the erection of the tank 

 and the saving in the cost of the oil will show an 

 earning on the investment. 



After describing existing municipal storage 

 plants, a simple form of single compartment tank 

 is suggested that will hold 12,000 gallons and is 

 fitted with steam coils and on which all outside 

 piping is steam jacketed, which will cost com- 

 plete approximately $700 and is capable of 

 handling all of the heavier grades of binding oils 

 and solid bitumens as well as the lighter grades 

 of road oil. 



The Consistency of Bituminous Materials, its 

 Determination and Value in Specifications: 

 Major W. W. Crosby, chief engineer to the 

 Maryland Geological and Economic Survey, and 

 consulting engineer, Baltimore, Md. 

 The consistency of a bituminous material is 

 defined as its degree of firmness and determined 

 by internal friction. 



The determination of consistency is now usually 

 made by one or more of half a dozen instruments 

 designed on three general principles. 



The instruments described, however, do not now 

 cover in their range the entire field of materials 

 and some materials are difficult of measurement 

 in the matter of consistency by any of the older 

 and more customary instruments. 



The desirability of a single instrument for the 

 purpose, whose range will cover readily the entire 

 field of materials, is evident. Two such, newly 

 proposed and as yet not generally used, are de- 

 scribed. A modification in the customary methods 

 of performing certain tests is advocated. 



The value of a proper determination of con- 

 sistency is shown by the dependence, on this 

 characteristic, of the methods of using a material, 

 by the information which such a determination 

 gives concerning the probable results of such use, 

 and concerning the value of the material itself. 

 Specifications containing definite descriptions of 



