BUEEAU OF PUBLIC ROADS. 



421 



be classified as follows : Rock, 202 ; concrete, 252 ; sand, 205 ; gravel, 

 151; slag, 54; cement, 49; miscellaneous, 111. Samples were re- 

 ceived from 41 States, and also from Canada. The geograx^liical 

 distribution of samples examined is as follows : 



Alabama 



Arizona 



Arkansas 



California 



Colorado 



Connecticut 



Delaware 



District of Columbia 



Florida 



Georgia 



Idabo - 



Illinois 



Indiana 



Iowa 



Kentuclcy 



Maine 



Maryland 



Massachusetts 



Michigan 



IMinnesota 



Mississippi 



Missouri 



Montana 



Nebraska 



2(j 

 8 

 6 



o 



9 



2 



lb 



47 



39 



10 



2 



15 



2 



o 

 O 



u 



9 

 32 



15 

 14 

 13 

 17 



8 

 13 



7 



Nevada 



New Hampshire 



New Jersey 



New York 



North Carolina _ 

 North Dakota--. 



Ohio 



Pennsylvania 



South Carolina _ 



South Dakota 



Tennessee 



Texas 



Utah 



Virginia 



Washington 



West Virginia 



Wisconsin 



Canada 



3 



7 



9 



7 



38 



1 



65 



39 



15 



2 



17 

 8 



14 



489 



1 



41 

 6 

 1 



Total 1,081 



Unclassified 3 



1,084 



MICROSCOPIC EXAMINATION AND CLASSIFICATION OF ROAD-BUILDING ROCK. 



The Petrographic Laboratory examined 686 samles of road-build- 

 ing material during the year, an increase of almost 9 per cent over 

 the preceding j-ear and well above the average of routine work. Of 

 these samples, 249 were rock, 41 slag, 151 gravel, 189 sand, 45 clay, 

 and 11 miscellaneous. 



Of the samples examined in the physical, chemical, and petro- 

 graphic laboratories, 355 were materials for use in Federal-aid con- 

 struction. 



RESEARCH ON DUST PREVENTIVES AND ROAD BINDERS. 



The following investigations have been under way on bituminous 

 materials: | 



1. Comparison of old and new volatilization tests in gas and electric ovens. 



2. Kxiiosure tests on bituminous materials of known chemical composition. 



3. Study of the distillation of California and Mexican peteroleum with refer- 

 ence to the manufacture of road oils. 



4. Bituminous joint fillers. 



5. Chemical composition of asphalts and tars. 



6. Methods of making float tests. 



7. Investigation of the action of copper salts on bituminous material.g. 



8. Investigation of the toughness of bituminous aggregates. 



One investigation on' the thickness of bituminous films on dilfcr- 

 ent types of aggregates has been completed and the data is reach' to 

 be worked up in form for publication. A study of the asphalt con- 

 tent of oils has also been completed and is ready to be put in shape 

 for publication. A paper is now being published on the micro- 

 scopic examination of bituminous materials. A paper on the Effi- 

 ciency of Bituminous Surfaces and Bituminous Pavements under 



