November "30, 191 1] 



NATURE 



147 



T 



DVST EXPLOSIONS. 



HE explosion of a mixture of dust and air, sup- 

 posed by the head of the firm of Messrs. Bibby 

 Brothers to have been the initiating- cause of the 

 catastrophe which destroyed and set on fire part of 

 their oil-cake and seed-crushing mills in Liverpool on 

 the night of November 24, is the most probable 

 explanation of that occurrence. It appears that some 

 of the seeds which contain no oil form an exceed- 

 ingly fine powder when crushed. The hypothesis is 

 that_ fine powder produced in this manner became dis- 

 seminated in the air of the chamber, thus forming an 

 inflammable mixture, and was ignited by some means 

 not ascertained, possibly by a stream of sparks due to 

 friction between the grinding rolls, possibly by an 

 open light. Be this as it may, a violent explosion 

 took place, shatteritrg that portion of the mill in which 

 crushing is carried ^•^*, and causing the deaths of 

 thirty-one persons, and, more or less, serious injuries 

 to 112 others. 



This event recalls the disastrous explosion which 

 destroyed the Tradeston Flour Mills in Glasgow in 

 1872, and was investigated and reported upon by 

 Profs. Rankine and Macadam. On that occasion 

 Prof. Macadam stated: "When the whole of the 

 conditions required theoretically for the most disastrous 

 explosions are practically realised, the increase of 

 pressure is equal to eight atmospheres or 120 lbs. 

 per_ square inch, which must necessarily bring about 

 a violent explosion and wreck any ordinary building." 



-Another notable explosion of the same kind, which 

 stands unrivalled in the magnitude of the havoc 

 wrought by it, wrecked the Washburn Flour Mills at 

 Minneapolis on May 2, 1878, and set fire to six other 

 mills and a number of buildings in the neighbourhood. 

 Profs. Peckham and Rye, who were commissioned 

 by the coroner's jury to investigate the circumstances 

 in which it took place, made a series of experi- 

 ments in closed boxes to test the explosibility of a 

 variety of powdered substances, amongst others vari- 

 ous flour mixtures and coal dust. The powders were 

 blown into the box with bellows and ignited by an 

 jOpen light. As the result of their experiments the 

 investigators came to the conclusion "that practically 

 fell finely divided highly carbonaceous material would 

 explode under the conditions tried." 

 . Explosions in grinding mills are not, perhaps, so 

 Infrequent as might be imagined : a dust explosion 

 occurred in an adjoining block in Messrs. Bibby's mill 

 pur years ago, when several workmen were injured 

 and many similar explosions have taken place in flour 

 mills from time to time, causing damage and setting 

 tire to the buildings, but not heard of beyond the 

 immediate locality, and then probably reported merelv 

 is fires. ■' r j 



Most mill owners seem to be now alive to the risks 

 jthey run from this cause, and take the precaution of 

 •jmiting the dimensions of the spaces in which mix- 

 •ures of dust and air are necessarily formed, and 

 Bxcuding open flames from them. Besides flour 

 mills, sugar refineries, starch works, and factories 

 for the preparation of madder, Ivcopodium powder, 

 flour of sulphur, and so on, have 'all been the scenes 

 af explosions of this kind. Lycopodium powder, 

 R'hich consists of the spores of L. clavatum the stag- 

 fiorn moss, is amongst the most inflammable of these 

 substances. It burns with a sudden flash of yellow 

 flame and with a hissing noise, probably due to the 

 bursting of_ the individual spores, when its mixture 

 ■vith air IS ignited. 



Lastly, the inflammable, and under certain condi- 

 pons explosive, nature of a mixture of air and coal 

 NO. 2196, VOL. 88] 



dust is now becoming better understood and appre- 

 ciated, and has recently constituted the subject or 

 articles contributed by the present writer to the pages 

 of Nature (vol. Ixxxvi., pp. 223, 595). 



W. Galloway. 



THE TEACHING OF MATHEMATICS.' 

 TpHESE two reports on mathematical teaching 



* cover very different ground, and are treated 

 from very different points of view. The report of 

 the London County Council refers particularly to 

 elementary schools, though in many places it deals 

 with general questions of mathematical teaching that 

 apply to schools of all types. The New South Wales 

 report refers entirely to the work of secondary schools. 

 Again, the L.C.C. report is drawn up by a body con- 

 sisting mainly of teachers in the closest touch with the 

 child, and, throughout their report, they consider the 

 state of development of the child's mind and the wide 

 differences there must be between the children in the 

 future. In marked contrast to this, the N.S.W. report 

 does not seem to be based on an intimate knowledge 

 of the minds of average pupils, but seems to aim only 

 at the production of future mathematicians. 



The L.C.C. report opens with a chapter devoted to 

 general questions of mathematical teaching; then 

 follows an excellent chapter on the first steps in arith- 

 metic. The next chapter, "On the coordination of 

 arithmetic with science and other subjects of the curri- 

 culum," is the most suggestive chapter in the report; 

 there are many excellent suggestions for changing the 

 arithmetic lesson from a dull grind to a really attrac- 

 tive lesson, instilling into the pupils a truly scientific 

 spirit. The only doubt that arises in our mind is 

 whether the second-rate teacher will keep a proper 

 balance between the illustrations leading up to new 

 ideas and the new ideas themselves — recent experience 

 in geometry shows that a word of warning is neces- 

 sary. The fourth chapter deals with the logical and 

 computative sides of the subject — some of the examples 

 considered seem to be the diabolical inventions of the 

 examiner or the text-book writer. Finally, we have a 

 summary of the answers to questions sent round fo 

 teachers,^ examiners, and inspectors — some of these are 

 of great interest ; the most interesting perhaps is taken 

 in the first chapter ; it deals with the " relative capacity 

 of boys and girls for mathematics " : — 



Opinions expressed were in favour of a greater general 

 capacity for mathematics, especially as tested by the solu- 

 tion of problems, among boys, and of greater neatness, 

 accuracy, and conscientiousness in carrying out rules and 

 processes, among girls. It was, however, stated that 

 many brilliant exceptions were to be found amongst the 

 girls. The evidence further went to show that the genius 

 is balanced by the dullard more often among groups of 

 boys than among groups of girls. " 



Altogether, the report is one of the most suggestive 

 contributions that have been made to the literature on 

 mathematical teaching in schools. We commend it 

 most heartily to all teachers in secondary as well as 

 elementary schools. 



In the N.S.W. report there is a paragraph near the 

 beginning which lays stress on the importance of co- 

 ordination in teaching the various branches of mathe- 

 matics, but it is not worked out in detail, and seems 

 to break down in one or two places ; e.g. in the second 

 year trigonometry is included under arithmetic, whereas 



1 London County Council. Education Committee. Report of a Con- 

 ference on the Teaching of Arithmetic in London Elemrntary Schools. 

 December 1906-Oecember 1908. Pp. 134. (London : P. .S. King and Co., 

 1511.) Price ijr. 



Memorandum on the Teaching of Elementary Mathematics.. By Prof. 

 H. S. Carslaw. Pp. 31. (Sydney, N.S.W. : Issued by the Department of 

 Public Instruction, n.d.) 



