1,VDC;sTRIAL A N D ENGISEERISG CHEMISTRY
November, 1925
After cooling, the varnish was poured onto 12.7-cm. square glass plates which were suspended in a vertical position until they no longer dripped, and were then set a t an angle of 60 degrees on shelves to dry. The varnish was considered to be dry when it was "dry to the touch"-i. e., when the plate no longer adhered to the finger-tip when touched. During the drying, observations were made of temperature and humidity of the air. These figures remained practically constant during the entire run of tests. The average air temperature was 22.4' C., and the average humidity was 54.98 per cent. The results are shown in the accompanying curves. There would seem to be little practical advantage in the use of more than 0.26 per cent of lead, and none a t all in the use of over 0.50 per cent. With manganese the most efficient amount is
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0.03 per cent, with the drying time increasing with further increase of metal. The lead curve is quite even and regular. The manganese curve takes no very definite form, but the point of major decrease is well marked, and there is an undoubted increase in drying time after a certain percentage of metal has been reached. The litharge-in-oil samples gave a very slight gradation of color and amount of sedimentation on standing. Above 0.50 per cent of lead the amount of sediment was excessive. The manganese-in-oil samples were practically uniform in color, slightly darker than the samples prepared with the use of litharge, but sedimentation was much more marked. Above 0.01 per cent of metal there was so much sediment present that the samples were practically opaque.
Determination of Temperature of Plasticity of Coals' By C. E. Foxwell KOPPERS COKEOVEN Co.,
LTD.,SHEFFIELD, ENGLAND
S THIS JOCRSAL, 17, 165 (19251, some work on this
It would have been preferable if the authors had measured subject is communicated by Layng and Hathorne. the temperatures inside the tube, and not outside as shown in This work, as the authors state, is carried out by a their diagram, as there is frequently a considerable lag. method very similar to that published by the writer in 1921,2 The use of a large bottle holding 12 liters of gas must be rebut they neglect the writer's more recent work on the ~ u b j e c t . ~garded as reducing the sensitiveness of the apparatus. If The method employed by Layng and Hathorne is open the gas in the holder is to be sufficient for an experiment which to several objections-a criticism which applies equally to may last for from 1 to 5 hours, the tube for conveying the the writer'> earlier method. The authors do not state a t water from the constant level must be sufficiently narrow to what rate the temperature of the coal was allowed to rise; allow the admission of only strictly moderate quantities of the rate of rise of temperature has little influence on the water per minute to the holder. When the resistance of the temperature at which plasticity commences, but it profoundly coal is increasing, a portion of this water is displacing gas affects the temperature of maximum pressure, the extent of which flows through the coal and another portion-sornethe plastic range, and the pressure developed. Thus, in times the major portion-is required to increase the pressure the case of three typical English coking coals the following in the apparatus as registered by the gage. The larger figures were found: the volume of the gas holder and gas-conducting tubes, the CornMax. -. re- - .-~less readily will fluctuation in the resistance of the plastic menceComsistance t o coal be detected. Rate of ment of Max. pletion as flow rise of plasresist- of plastic M B m W. G./ The question of weathering mentioned by Layng and temp. ticity ance stage cm./cc. gas COAL C./rnin. C. C. C. passed Hathorne has been dealt with to some e ~ t e n t . ~ 375 420 460 13.S South Wales 1 The complete method as finally adopted by the present 3 375 440 500 144.0 5 380 450 530 484.0 writer was published in FueL6 It is realized that the method 470 142.0 North Yorkshire 1 355 370 there described is only of value as a research method, since 365 450 560 617 5 490 39 South Yorkshire 1 380 448 the time and labor involved in both experiment and calcula380 460 530 24 1 3 390 480 560 690 5 tion are much greater than could be contemplated for freI t must here be observed that there is no definite tempera- quent use in a works laboratory. An investigation has ture of completion of the plastic stage; the coke continues therefore been undertaken to discover a simpler method to drop slightly in resistance for as much as 200" or 300" C. which shall show clearly the essential characteristics of the I n Layng and Hathorne's experiments no precautions were coal under examination, without requiring laborious calcutaken to prevent the coal from expanding. The sample was lation. A survey of the experiments so far completed shows that allowed to rest on coiled copper wire and was not confined in any way at the upper surface. Under these circumstances if the rate of rise of temperature above 300" C. is fixed a t coking coals may expand to a surprising extent and, although 1 C. per minute and the pressure is expressed in centimeters occupying a length of, say, 5 cm. a t the commencement of of water, a pressure-temperature curve is obtained which the plastic stage, may occupy 8 to 10 cm. a t the end, thus without any corrections approximates fairly closely the more showing a lower resistance to gas flow, owing to the develop- accurate curve obtained by the methods described in Fuel. The temperatures of incipient and final plasticity are given ment of large pores, than should be the case. This expansive force of coal in the plastic stage may be very great and has accurately, but the temperature of maximum resistance is frequently been found sufficient to break thick combustion on the average 5.5" C. too high. At more rapid rates of glass and fused silica.4 The difficulty may be overcome by heating the uncorrected curve may or may not tally with the the use of a special device and by packing the tube contain- corrected curve. Thus, with 3" C. rise per minute 70 per cent of the curves tallied, 10 per cent were doubtful, and 20 per cent ing the coal with carefully graded fire brick. -composed entirely of coals from a certain area-were 1 Received May 7, 1925. 2 J SOC.Chem Ind , 46, 193T (1921). definitely unsatisfactory.
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O
8 4
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Fuel, 3, 122, 174, 206, 227, 276, 315, 371 (1924) I b i d . , 8, 123 (1924).
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F u e l . 3, 122 (1924)
