812 
Journal of Agricultural Research 
Vol. V, No. 17 
This being so, the average of results given in Table II can best be con¬ 
sidered by means of Table IV, in which are given the average penetrations 
obtained on all of the samples under various conditions of cooling prior to 
1% hours’ immersion in water. A study of this table shows in every case 
a gradual hardening or lowering of penetration as the time in air is 
increased. This lowering in penetration is not very pronounced in a 
period of 24 hours, but it increases quite appreciably in longer periods. 
Allowing for slight experimental errors, no difference is found to exist 
between the 30-minute and i-hour exposure in air. The most marked 
difference is, of course, apparent between the results of 28 days in air as 
compared with 30 minutes in air, and the greatest difference in actual 
points of penetration will in every case, for a given type of material, be 
found for the softest grade of that type, or, in other words, for that grade 
which originally showed the highest penetration. It is apparent that 
no permanent set occurs up to a period of 28 days, but that a gradual 
hardening takes place. This being so, it is of interest to compare the 
foregoing with the results obtained by immersion in ice. water prior to 
immersion in the water bath for 1 % hours at 25 0 C. It will be seen, in 
general, that but little difference in results is obtained between the 
samples cooled in ice water and those cooled in air, although under certain 
conditions for the short periods a slightly lower penetration has been 
secured by this means. It is safe to say, however, that the immersion of 
the sample in ice water does not produce a set which is comparable to 
any definite set produced by prolonged standing in air. This is evident 
from the last series of results, in which the samples which had been 
immersed in ice water for an hour were allowed to stand 28 days before 
immersing them in the water bath, the results in each case being appre¬ 
ciably lower than those obtained by immersing them for 1 hour in ice water 
and then 1 hours in the bath just prior to test. There does not there¬ 
fore, appear to be any good reason for cooling the sample in ice water at 
any time, except, perhaps, in plant-control work, where it is desired to 
expedite the test somewhat, and an allowance can be madefor variations 
from the ordinary method caused by the ice-water immersion. 
Table IV .—Comparison of average penetrations at 25 0 C. after 1 % hours * immersion in 
bath, 100 gm., 5 seconds 
Conditions before test. 
In air. 
In ice. 
In air. 
30 min. 
1 hr... 
24 hrs. 
3 days. 
7 days. 
28 days. 
30 min. 
s8days(re- 
melted). 
30 min 
1 hr 
30 min.... 
30min.... 
30 min. 
x hr... 
x hr... 
28 days. 
California. 
Mexican. 
Blended. 
Blown. 
8961 
8962 
8963 
8948 
8949 
8950 
8994 
8995 
8996 
8956 
8957 
8958 
47 
93 
133 
50 
90 
*50 
62 
92 
*57 
44 
9* 
*36 
46 
95 
134 
50 
90 
*47 
61 
93 
*58 
42 
9* 
136 
45 
93 
131 
47 
86 
*42 
58 
88 
150 
41 
89 
132 
44 
90 
130 
45 
83 
*39 
54 
85 1 
*44 
42 
68 
128 
43 
85 
xas 
45 
78 
X31 
53 
82 
142 
42 
85 
xa8 
38 
79 
**9 
39 
70 
**4 
48 
73 
*3* 
38 
78 
1x2 
46 
95 
133 
49 
9* 
X48 
6x 
89 
XS6 
42 
93 
*36 
47 
93 
131 
49 
90 
*5* 
61 
94 
*57 
43 
9* 
*35 
47 
94 
133 
49 
87 
146 
60 
92 
152 
4» 
9* 
136 
46 
93 
132 
49 
88 
146 
60 
93 
*53 
43 
9* 
*35 
47 
92 
*33 
48 
87 
*4« 
59 
92 
150 
43 
92 
*34 
37 
79 
**9 
38 
68 
*24 
48 
74 
*3* 
37 
76 
XXX 
