SAMPLING AND TESTING HIGHWAY MATERIALS. 



45 



equal distances from the bottom and serve for measuring the charge of material, 

 which is 240 c. c. The thermometer e is used to ascertain the temperature of the ma- 

 terial to be tested. The vessel a is surrounded by a brass jacket, /, which holds the 

 material used as a heating bath, either water or cottonseed oil, according to the tem- 

 perature at which the test is to be made. A tripod, g, serves as a support for the 

 apparatus and also carries a ring burner h, by means of which the bath is directly 

 heated. The measuring cylinder of 100 c. c. capacity, which is sufficiently accurate 

 for work with road materials, is placed directly under the outflow tube. 



As all viscosity determinations should be compared with that of water at 25° 0., 

 the apparatus should be previously calibrated as follows: The cup and outlet tube 

 should first be scrupulously cleaned. A piece of soft tissue paper is convenient for 

 cleaning the latter. The stopper is then inserted in the tube and the cup filled with 

 water at 25° 0. to the top of 



the projections, 

 uring cylinder 

 placed directly 

 outflow tube so 



The meas- 



should be 



under the 



that the 



a 



s— 



o 



material, upon flowing out, 

 will not touch the sides, and 

 the stopper may then be re- 

 moved. The time required 

 both for 50 and 100 c. c. to 

 run out should be ascer- 

 tained by means of a stop 

 watch, and the results so ob- 

 tained should be checked a 

 number of times. The time 

 required for 50 c. c. of water 

 should be about 11 seconds 

 and for 100 c. c. about 22.8 

 seconds. 



Bituminous road mate- 

 rials are tested in the same 

 manner as water, and the 

 temperature at which the 

 test is made is controlled 

 by the bath. The material 

 should be brought to the desired temperature and maintained there for at least three 

 minutes before making the test. The results are expressed as specific viscosity 

 compared with water at 25° C, as follows: 



^. 



I<'ig. 23. — Engler viscosimeter. 



Specific viscosity at A° 0. 



seconds for passage of given volume at A°C. 



seconds for passage of same volume of water at 25° C. 



28. DETERMINATION OF PERCENTAGE OF RESIDUE OF DESIRED 



PENETRATION. 



Fifty grams of the oil are placed in a 3-ounce deep, seamless tin box; the box is 

 placed in a sand bath and heated over a Bunsen burner. A thermometer is suspended 

 in the oil, the bulb not touching the bottom of the box. The temperature of the oil 

 is kept at from 249° C. (480° F.) to 260° C. (500° F.), and the oil is stirred from time 

 to time with the thermometer to prevent overheating in any part. Depending upon 

 the nature of the oil, as usually indicated by its flash, consistency at 25° C. (77° F.) 

 and specific gravity, the operator can with experience tell about what percentage it 

 will be necessary to evaporate before cooling and taking a penetration of the residue. 



