O81 
the thermo couple indicated a temperature close to that at which there 
was prospect of an oily deposit, the paper rolls were put in place, the 
paper marked and the test started. When the tar commenced to show up 
the temperature of the furnace was recorded and the pipe (15) changed 
every 10 minutes. As the temperature of the furnace rose to 300° C. the 
current was increased } of an ampere, at 400° © 4 of an ampere more, and 
at 500° GC. % of an ampere. This was done to take care of the increased 
radiation, and to keep the rise in temperature at a constant rate. When 
the paper ceased to show any signs of a tar deposit it was again marked 
and timed and the current shut off. ‘The strip of paper was then cut up 
into lengths corresponding to 10 minute periods, and carefully weighed. 
As the weight of the paper per inch was very constant, the excess in weight 
over that of clean paper was in each case due to the tar. From this two 
curves could be drawn, with time plotted horizontally, while one had 
temperature centigrade and the other grams of tar plotted vertically. 
These curves when placed one right over the other, as here given in hig 3, 
indicate the amount of tar coming off at each temperature. The points 
where the tar starts and stops can not be indicated by this curve, is 
the ends of the deposit are too thin to have appreciable weight. ‘They are 
consequently separately noted elsewhere. 
The first condensible gas to be driven off from the coal and appear 
on the paper record is water vapor. After the last of the water has 
disappeared there is quite a temperature range through which there is 
no deposit at all. Then the paper will begin to show a slight trace of 
oil. This will gradually increase in amount and give the paper the ap- 
pearance of having been parafined. The deposit will then gradually as- 
sume a brownish color, as though engine oil were appearing. Later a 
temperature will be reached at which the deposit will increase very 
rapidly in amount, and will assume a distinctly tarlike appearance. The 
first tar to be deposited is usually very soft and sticky at room tempera- 
ture. As the temperature rises the tar becomes steadily stiffer, until it 
is finally hard and brittle when cooled. The temperature range through 
which the maximum deposit occurs will vary from about 100° C., for some 
western coals, to 175° for some of the samples from the east. At the 
higher limit of this range the deposit becomes rapidly smaller in amount 
until it is too small to weigh, but the paper is still distinctly browned. 
This discoloration becomes less and less plain, until it finally disappears 
entirely. There is no definite temperature at which the first and the last 
