2 BULLETIN" 314, U. S. DEPARTMENT OF AGRICULTURE. 



Special attention is called to modifications in the penetration test, 

 determination of fixed carbon, and determination of paraffin scale; 

 and to the substitution of new methods for the old distillation tests 

 and for determination of voids in the mineral aggregate. In addition 

 descriptions of the following methods, which were not included in 

 Bulletin No. 38, are given: 



(1) Determination of flash and burning points — open cup method. 



(2) Dimethyl sulphate test. 



(3) Methods of examining bituminous emulsions. 



While it is realized that the following scheme of examination is 

 not perfect and may in the future be improved, it has nevertheless 

 been of great assistance in classifying bituminous road materials and 

 determining their suitability for use according to various methods of 

 application and construction. 



CLASSIFICATION OF BITUMINOUS ROAD MATERIALS. 



For the purpose of examination bituminous road materials' may 

 be classified under the following headings: 



1. Petroleums and petroleum products, including heavy distillates, malthas, resid- 

 ual petroleums, fluxes, oil-asphalts, and fluxed or cut-back oil-asphalts. 



2. Asphalts and other solid native bitumens, and asphaltie cements produced by 

 fluxing them. 



3. Petroleum and asphalt emulsions. 



4. Tars and tar products. 



5. Mixtures of tar with petroleum or asphalt products. 



6. Bituminous aggregates, including rock asphalts or bituminous rocks, bituminous 

 concrete, asphalt block, and bituminous topping. 



SCHEME OF EXAMINATION. 



All petroleum, maltha, and solid native bitumen products are sub- 

 jected to the following tests: 



Specific gravity. 



Volatilization at 163° C. 



Bitumen soluble in carbon disulphide. 



Bitumen insoluble in 86° B. paraffin naphtha. 



Fixed carbon. 



Of these types the very fluid and sometimes the more viscous 

 products may be subjected to the viscosity, flash, and buming-pomt 

 determinations. Very viscous materials, too soft for the penetration 

 test, are subjected to the float test, and semisolid and solid products 

 to the penetration test. If the material is sufficiently hard at ordinary 

 temperatures, a melting-point determination may also prove of value. 

 Sometimes two or more of the above-mentioned tests, depending upon 

 the character of the material and the use to which it is to foe put, may 

 be made to advantage on a single material. When for any reason it 

 is suspected that the material under examination has been overheated 



