January i6, 19 13] 



NATURE 



55: 



have been shown by Bedson to be extractable in con- 

 siderable quantity from coal by the action of pj'ridine ; 

 and that the inflammability of any particular kind of 

 coal dust depends more upon the proportion of 

 paraffin-yielding substances contained in it than upon 

 that of its volatile matter considered as a whole. 



The apparatus employed by the Committee for 

 ascertaining the temperature of ignition of different 

 kinds of coal dust resembles that previously employed 

 for the same purpose by Bedson and Widdas, and by 

 Taffanel, in so far that, in each, a small cloud of fine 

 dry dust (i or 2 grams) is projected by a puff of air into 

 a tube, or closed space, in which it is raised to the 

 temperature of ignition b)' coming more or less closely 

 into contact with an electrically-heated surface or 

 spiral of platinum wire. Bedson and Widdas had no 

 means of measuring the temperature of ignition 



Fig. 2.— Apparatus for giving a constant puff of air.— A brass cjlinder 

 65 cm. long and of ii cm. internal diameter is fitted with a weighted 

 piston. For the experiments, the weight employed is such as to give a 

 pressure of 2 lbs. per sq. in. 



directly, but hoped to determine it by calculation from 

 the varying number of amperes required to effect 

 ignition with different kinds of dust. In this they 

 were disappointed in consequence of the alteration 

 which the coil of platinum wire underwent owing to 

 the adhesion of particles of dust to it. Taffanel and 

 the Committee, on the other hand, both measure the 

 temperature by means of a thermo-couple. It will be 

 sufficient, for present purposes, to describe the appli- 

 ances used by the Committee. 



The puff of air is produced by opening a stopcock 

 B, Figs. I and 2, in a tube one end of which com- 

 municates with the interior of a vertical brass cylinder 

 at its bottom end. The cylinder, which is 65 cm. 



NO. 2255, VOL. go] 



long by II cm. in diameter, is provided with a 

 weighted piston, which gives a pressure of 2 lb. per 

 sq. in. to the air in its interior. The other end of 

 the tube with the stopcock is connected to a larger 

 tube A (Fig. i), 2^5 cm. in diameter by 45 cm. long, 

 in which a charge of about 2 grams of sieved and 

 dried dust is laid along the bottom. The latter tube 

 is supported near the upper side of a third horizontal 

 glass tube, 8 cm. in diameter by 140 cm. long, open 

 at both ends, as shown. A thin-walled quartz tube 

 of capillary bore, with a platinum coil of 32 gauge 

 wire, 17 mm. long by i'5 mm. in diameter, closely 

 wound upon its outside, and with a platinum and 

 platinum-rhodium thermo-couple passing through it, 

 extends horizontally across a diameter of the larger 

 tube at a point 40 cm. from one end. The thermo- 

 couple is connected to a mille-voltmeter calibrated to 

 read to temperatures on the Centigrade scale. The 

 cross-section in Fig. i shows the disposition of the 

 various connections and the position of the platinum 

 spiral. By the adjustment of an e.xternal resistance 

 the coil can be heated to any desired temperature up 

 to 1400° C. 



If ignition takes place freely when the dust-cloud 

 is puffed into the combustion tube, the temperature 

 of the coil is lowered 10 or 20 degrees, and another 

 trial made, and so on, until the dust-cloud does not 

 ignite. The mean of the two last observations is 

 then taken as the ignition-temperature. 



The following observations regarding the dust of a 

 coal (224 N) containing 2' 11 per cent, moisture, 35'7o 

 per cent, volatile matter, jg'gg per cent, fixed carbon, 

 and 2'2o per cent, ash, which was passed through a 

 240 mesh sieve, and dried for an hour at 107° C, may 

 be given as an illustration of the method of finding 

 the temperature required : — 



1040° C. Ignition. Flame propagated rapidly 



to end of tube. 

 1020° C. Ignition. Slow propagation of flame. 



1000° C. No ignition. 



1010° C. No ignition. A few sparks round 



coil. 

 Ignition-temperature, 1015° C. 



Fig. 3 shows two photographs of the flames pro- 

 duced in this apparatus. 



A table on p. 9 gives the relative ignition-tempera- 

 tures of a number of different dusts the total volatile 

 matter of which, calculated on ash-free dry coal, 

 varies from 4i'77 per cent., with an ignition-tempera- 

 ture of 1065° C, to 26'02 per cent., with an ignition- 

 temperature of 1095° C. The intermediate results are 

 so incongruous amongst themselves that the Com- 

 mittee can discover no relationship between the per- 

 centages of volatile matter and the ignition-tempera- 

 tures. 



On the other hand, a similar table on p. 10, which 

 gives the percentage extracted by pyridine, shows also 

 that while the dust of one coal with a total proportion 

 of volatile matter amounting to 32^14 per cent., and 

 a percentage of 37'g extracted by pyridine, ignites at 

 a temperature of 1005° C, tji'at of another, containing 

 36'3 per cent, of volatile mattrr, and a percentage 

 of only 22' I extracted by pyridine, requires a tem- 

 perature of 1090° C. to produce ignition. 



While fully alive to the fact tfiat the relationship 

 between ignition-temperature and percentage extracted 

 by pyridine cannot he expected to hold rigidly, the 

 Committee is of opinion that the results obtained up 

 to the present are encouraging, and intends to con- 

 tinue the investigation on the same lines. 



