630 



NA TORE 



[October 26, 189; 



sequent absorption of oxygen. This sets up chemical com- 

 bination between the oxygen absorbed by the coal and the 

 hydrocarbons, and in some cases culaiinates in combustion. 



It is found that the mas; of coal exercises a most important 

 action in the liability to spontaneous combustion, as although 

 with 500 tons of coal to the cargo the cases of spontaneous com- 

 bustion amount to only about \ per cent, when the bulk is 

 increased to 2000 tons, cases of spontaneous combustion rise to 

 9 per cent., this being due to the fact that the larger the cargo 

 the more non-conducting material will there be to keep in the 

 heat, and also to the fact that the breaking-up of the coal and 

 the exposing fresh surfaces will of course increase with increase 

 in mass ; and it is also found that coal cargoes sent to European 

 ports rarely undergo spontaneous combustion, whilst the number 

 of cases rise to a startling extent in shipments made to Asia, 

 Africa, and America. The result is party due to the length of 

 time the cargo is in the vessel, the absorption and oxidation 

 being a comparatively slow process, but the main cause is the 

 increase of heat in the tropics, which causes the action to become 

 more rapid ; and if statistics had been taken, most of the ships 

 would have been found to have developed active combustion some- 

 where about the neighbourhood of the Cape, the action fostered 

 in the tropics having raised the temperature to the igniting point 

 by that time. 



Moisture has a most remarkable effect upon the spontaneous 

 ignition of coal. The absorption of oxygei> is at first retarded 

 by external wetting, but after a time the presence of moisture 

 accelerates the action of the absorbed oxygen upon the coal, and 

 so causes a serious increase of heat. The researches of Cowper, 

 Baker, Dixon, and others, have of late years so fully shown the 

 important part which moisture plays in actions of this kind, that 

 it is now recognised as a most important factor. A very marked 

 case of the influence of moisture came under my notice a few 

 months ago. A ship took in a cargo of coal at a South Welsh 

 port, the weather being fine and dry whilst she was loading at 

 the main hatch, but wet whilst she was taking in the coal at the 

 after-hatch, the result being that the temperature in a few days 

 was uniformly about 10° higher in the coal that had been 

 loaded wet, than in the dry portion of the cargo, spontaneous 

 ignition being the final result at the after-hatch. 



In order to prevent the spontaneous ignition of large masses 

 of coal, it is manifest that every precaution should be taken 

 during loading or storing to prevent crushing of the coal, and on 

 no account must a large accumulation of small coal be allowed. 

 Where possible the depth of coal in the store should not 

 exceed 6 to 8 feet, and under no conditions must steam-pipes or 

 flues be allowed so near the mass of coal as to give rise to any 

 increase of temperature. These precautions would amply suffice 

 to prevent spontaneous ignition in stored coal on land, whilst 

 special precautions would have to be taken in the case of coal 

 for shipment. 



Perhaps: he commonest case of spontaneous combustion is 

 the ignition of oily waste or greasy cotton rags. Nearly all 

 vegetable and animal oils have the power of slowly absorbing 

 oxygen, and in some of them this goes on with considerable 

 rapidity, with conversion of the oil into a resin, a properly 

 which gives them the power of drying, and causes a consider- 

 able rise of temperature. A mass of oil, however, only ex- 

 poses a very small surface to the oxidising influence of the 

 air, but when such oil comes to be spread upon any non- 

 conducting fabric, the oxidisation is very rapid, and the non- 

 conducting power of the fibre of the fabric prevents the rapid 

 dispersion of the heat, with the result that even a small quantity 

 of such oily substance will readily inflame. 



There are plenty of well authenticated cases in which even 

 a handful of oily cotton waste, which has been used for polish- 

 ing furniture, has ignited when thrown on one side, and caused 

 most disastrous fires. Just twenty years ago Mr. Galletly read a 

 most valuable paper before the Chemical Section of the British 

 Association, in which he showed that the liability of oils to 

 produce spontaneous combustion was in proportion to their 

 tendency to dry. If a substance like cotton-waste be rendered \ 

 oily with anything except the mineral oils, it acquires the power 

 of taking up oxygen from the air, and this gives rise to heat. 

 The oxidation is slow at ordinary temperatures, and accord- 

 ingly it may be some time before the increase of temperature 

 becomes manifest ; but when this point is reached, the action 

 proceeds with great rapidity, and the point of ignition is reached 

 in a very short time, and then the mass bursts into flame. If the 

 oily matter be placed in a warm position at first, spontaneous 



NO. 1252, VOL. 48J 



ignition may take place within a few hours, or even minutes. 

 Galletly found that oily cotton at ordinary temperatures took 

 some days to heat and ignite, whilst if placed in a chamber 

 warmed to 130° to 170" F. (54° to 76° C.) the cotton greasy 

 with boiled hnseed ignited in I hour 15 minutes, and olive oil 

 on cotton in 5 hours ; and in a chamber heated to l8o° to 

 200° F. (82° to 93° C.) olive oil on cotton ignited in two 

 hours. 



Cases of spontaneous combustion, due to this cause, have 

 been more abundant than from any other, and cases are even on 

 record where serious fires have resulted from sparrows using 

 oily waste in the construction of their nests. In all well- 

 regulated workshops the orders against allowing any accumula- 

 tion of oily waste are very stringent, and the most reasonable 

 precaution to be taken is that all oily material, when done with, 

 should be thrown into a metal^vessel containing water, or which, 

 at any rate, can be either emptied of waste or filled with water 

 at night. If a sheet of cotton be hanging in a warm room and 

 is splashed with oil, a hole will often be found charred in the 

 fabric by the next morning, whilst if a few drops of a drying oil 

 be allowed to fall on powdered charcoal or lamp-black, ignition 

 is almost certain to follow in a few hours. 



Another common case of spontaneous ignition is that of hay- 

 stacks which have been made up before the grass has been 

 thoroughly dried, this being due to the sap left in the vegetable 

 fibre undergoing fermentation, which being a process of oxida- 

 tion gives rise to heat. This heat is kept in by the surrounding 

 hay, which is an admirable non-conductor of heat, and gradually 

 increases until the ignition point of the mass is reached, when 

 the stack bursts into flame. In some cases the action does not 

 go as far as this, and we oftensee theinsideof a haystack charred 

 to an almost black colour, showing that the action has stopped 

 but little short of the point required to give active combustion, 

 this being probably due to the stack having been very closely 

 built, and the access of air to the centre being small, and in some 

 cases, when such a rick is cut, the air coming in contact with 

 the central portion causes active ignition. If hay has once 

 been properly dried, and then becomes wetted with rain, spon- 

 taneous ignition hardly ever takei place, although the hay 

 becomes mouldy, and it is evident that the action which leads 

 to ignition of the hay is fermentation of the sap. 



Having now discussed the more common cases of spontaneous 

 ignition, and seen that in every case it is due to rise of tem- 

 perature, brought about by chemical action until the igniting 

 point of the sutjstance is reached, we are in a position to under- 

 stand the impossibility of spontaneous combustion taking place 

 in the human body. 



The process of respiration by which the tissues of the body 

 used up in every action, voluntary or involuntary, are got rid of 

 by a process of slow combustion, gives a normal temperature to 

 the living body, and it might seem, at first sight, possible by pre- 

 venting the escape of such temperature, to increase it to a point 

 at which ignition might be possible ; but we know by experience 

 that the effect of swathing the body in non-conducting materials, 

 so as to prevent the escape of heat from it, results in profuse 

 perspiration, and before the living flesh could undergo com- 

 bustion it would be necessary to drive from it the whole of the 

 moisture which it contains. 



The human body contains from 75 to 80 per cent, of its 

 weight of water, and in order to evaporate this amount, an 

 enormous amount of heat would be required, and life would 

 have been impossible long before the necessary dryness of the 

 mass had been arrived at. In fact, the moisture present in the 

 body may be looked upon as its great safeguard against the' 

 effect of heat, and it is perfectly possible for a living man to re- 

 main in an oven which would roast a steak or cook an egg ; the 

 evaporation of water from the skin taking up so much heat th.it 

 the temperature of the living flesh would never rise above a cer- 

 tain point until the moisture was exhausted. It used to be sup- 

 posed that the cases of spontaneous combustion took place in 

 people whose intemperate habits had caused the body to become 

 saturated with alcohol, and that it was this substance which 

 caused its ready ignition ; but as Liebig pointed out, some forty 

 years ago, the presence of the alcohol could have no effect, as if 

 we take a sponge and soak it in spirits of wine and ignite it, 

 the alcohol burns away and leaves the sponge untouched, and 

 the same thmg would undoubtedly happen in the case of the 

 living flesh. 



In this lecture I have tried to bring before you the important 

 fact that spontaneous combustion merely means that the heat due 



