SAMPLING AND TESTING HIGHWAY MATERIALS. 



47 



(5) x\ny apparatus which will allow the needle to penetrate without appreciable 

 friction, and which is accurately calibrated to yield results in accordance with the 

 definition of penetration will be acceptable. 



(6) The transfer dish for container shall be a small dish or tray of such capacity as 

 will insure complete immersion of the container during the test. It shall be provided 

 with some means which will insure a firm bearing and prevent rocking of the 

 container. 



HI. PREPARATION OF SAMPLE. 



(7) The sample shall be completely melted at the lowest possible temperature and 

 stirred thoroughly until it is homogeneous and free from air bubbles. It shall then 

 be poured into the sample container to a depth of not less than 15 mm. (f inch). The 

 sample shall be protected from dust and allowed to cool in an atmosphere not lower 

 than 18° C. (65° F.) for one hour. It shall then be placed in the water bath along 

 with the transfer dish and allowed to remain one hour. 



IV. TESTING. 



(8) (a) In making the test the sample shall be placed in the transfer dish filled 

 with water from the water bath of sufficient depth to completely cover the container. 



Fig. 25. — Dow penetration ma< bine. 



The transfer dish containing the sample shall then be placed upon the stand of the 

 penetration machine. The needle, loaded with specified weight, shall be adjusted 

 to make contact with the -surface of the sample. This may be accomplished by making 

 contact of the actual needle point with its image reflected by the surface of the sample 

 from a properly placed source of light. Either the reading of the dial shall then be 

 noted or the needle brought to zero. The needle is then released for the specified 

 period of time, after which the penetration machine is adjusted to measure the dis- 

 tance penetrated. 



At least three tests shall be made at points on the surface of the sample not less than 

 1 cm. (| inch) from the side of the container and not less than 1 cm. (f inch) apart. 

 After each test the sample and transfer dish shall be returned to the water bath and 

 the needle shall be carefully wiped toward its point with a clean, dry cloth to remove 



