i4 BULLETIN 314, U. S. DEPARTMENT OF AGRICULTURE. 
The needle should be removed and thoroughly cleaned by wiping 
with a dry cloth, after which it is ready for another test. The point 
of the needle should be examined from time to time with a magnifying 
glass to see that it is not injured in any way. If it is found defective, 
it may be removed by heating the brass rod and withdrawing with 
pliers. A new needle may then be inserted in the heated brass rod, 
and held firmly in place by a drop of soft solder. 
USE OF PENETRATION TEST. 
This test is made on al! semisolid and solid oil-asphalts, asphaltic 
cements, and native asphalts, but seldom on tar products. It is 
also often made on the residues of materials subjected to the volatiliza- 
tion tests, when they are sufficiently hard. For work on residues, 
which seldom amount to more than 20 cubic centimeters, a small 
container, which should not, however, be less than 1 inch in diameter, 
will be required. : 
While the standard conditions under which this test is made call 
for a 100-gram load applied for five seconds on the material main- 
tained at a temperature of 25° C., it is sometimes desirable, when 
very soft materials are tested, to make the test with a 50-gram 
weight. In order to ascertain how susceptible a material may be to — 
temperature changes, tests may be made at any other desired tem- 
peratures, preferably 0° C., with a 200-gram weight for one minute, 
and at 46° C. with a 50-gram weight for five seconds. ' 
In all cases the results of tests should be reported in hundredths 
of a centimeter, as follows, showing all the conditions in order that 
no misinterpretation of results may occur: 
Penetration. ( seconds, grams at ——° €.)= —_. 
MELTING POINT DETERMINATION. : 
EQUIPMENT 
1 iron tripod. 
1 Bunsen burner and rubber tubing. 
i piece of wire gauze 10 centimeters square. 
1 800 cubic centimeter Jena glass beaker,-low form. (Fig. 8-a.) 
1 400 cubic centimeter Jena glass beaker, tall, without lip. (Fig. 8-b.) 
1 iron ring support (ring 7.5 centimeters in diameter) and burette clamp. (Fig. 8-c.) 
i metal cover. (Fig. 8-d.) 
1 object glass. 
1 piece of wire (No. 12 Brown & Sharpe gauge) 20 centimeters in length, bent. (Fig. 
8-e.) < 
1 chemical thermometer reading from 0° GC. to 250° C. 
1 cubical brass mold. (Fig. 8-/.) 
1 large metal kitchen spoon. 
1 steel spatula or kitchen knife. 
