2 BULLETIN 314, U. S. DEPARTMENT OF AGRICULTURE. 
Special attention is called to modifications mn the penetration test, 
determination of fixed carbon, and determmation 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 followmg 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 bitumimous 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 asphaltic 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 asphalis or bituminous rocks, bituminous 
concrete, asphalt block, and bituminous topping. 
SCHEME OF EXAMINATION. 
ow 
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 burnmg-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 determimation 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 be 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 
