CHANGES IN MOISTURE CONTENT. 
13 
following heading, showing the rapid changes in moisture in coal 
samples when spread on the watch glass, indicate that there is proba- 
bly a slight gain or loss of moisture in the ball-mill sample even dur- 
ing the short time that this sample is exposed to air during sampling, 
and that this change may be considerable if the coarse sample be very 
far from an air-dried condition before being ground down. The 
grinding down of samples in the ball mill can not, therefore, be con- 
sidered as perfectly satisfactory in so far as moisture changes are 
concerned; but this method of grinding, in connection with the pre- 
liminary drying of the coarse sample, is much more satisfactory and 
reliable than any other practical method that has been devised of 
which the writer has any knowledge. Therefore it appears that the 
handling of samples in this manner, as compared with the practice in 
most general use, is an important step in the direction of securing a 
sample for analysis with a minimum amount of unaccounted-for changes 
in moisture. 
CHANGES IN MOISTURE CONTENT OF FINE SAMPLES OF COAL UNDER 
MODIFIED CONDITIONS. 
That coal in a fine condition changes rapidly in moisture content is 
well known. In order to obtain definite information as to the rate of 
this change a number of tests were made on coals under different con- 
ditions. The first selection for testing was a fine sample (No. 1638 C) of 
undried Illinois coal, containing 12.4 per cent moisture. One gram 
of this sample was spread out on a 4-inch watch glass and weighed at 
intervals, a record of the temperature and humidity being taken 
at the time of the different weighings. A second series of tests was 
also made on a 10-gram portion of this sample spread upon a 4-inch 
watch glass. A third series of tests was made upon another portion 
of this sample (17.2 grams) by allowing it to stand in an open, wide- 
mouthed 2-ounce bottle and weighing at intervals. The results for 
these three series of tests are as follows: 
Changes in moisture content of sample (No. 1638 C) of undried Illinois coal. 
FIRST SERIES— 1 GRAM ON 4-INCH WATCH GLASS. 
Air of laboratory. 
Time interval between weighings. 
weight. 
Tempera- 
ture. 
Humid- 
ity. 
Grams. 
-0. 0202 
- .0075 
- .0090 
- .0110 
- .0350 
- .0120 
+ .0140 
+ .0060 
- .0127 
+ .0007 
- .0175 
Per cent. 
- 2.02 
- .75 
- .90 
- 1.10 
- 3.50 
- 1.20 
+ 1.40 
+ .60 
- 1.27 
+ .07 
- 1.75 
° a 
22 
Per cent. 
21 
25 
24 
28 
25 
18 
27 
32 
32 
50 
36 
36 
63 
64 
35 
41 
55 
10.42 
