SAMPLING AXD TESTING HIGHWAY MATERIALS. 
75 
contaminate the mercury. The pressure of the gas shall be 
ficient to prevent separation of the mercury column at all tem- 
peratures of the scale. There shall be a reservoir above the 
final graduation large enough so that the pressure will nut be- 
come excessive at rhe highest temperature. The thermo 
shall be finished at the top with a small glass ring or button 
suitable for attaching a tag. Each thermometer shall have for 
identification the maker's name, a serial number, and the le't^rs 
"A. S. T. M. Distillation." 
The thermometer' shall be graduated from 0° to 400° C. at 
intervals of l 3 ('. Every fifth graduation shall be longer than 
the intermediate one--, and every tenth graduation beginning at 
Fig. 11. — Asbestos shield. 
zero shall be numbered. The graduation marks and numbers 
shall be clear-cut ami distinct. 
The thermometer shall conform to the following dimensions: 
Total length, maximum: 385 millimeters. 
Diameter of stem: 7 millimeters: permissible variation. 
0.5 millimeter. 
Diameter of bulb, minimum: 5 millimeters; and shall not 
exceed diameter of stem. 
Length of bulb; 12.5 millimeters: permissible variation 
2.5 millimet< 
Distance, <>"- to bottom of bulb: ."><> millimeters; permissible 
variation. 5 millimeters. 
Distance, C to 400° : 295 millimeters ; permissible variation. 
10 millimeters. 
