Sept. ist, 1887.] 



SCIENTIFIC NEAVS. 



159 



than olive oil, linseed oil, etc. They are able to burn with- 

 out a wick at comparatively low temperatures, whilst the 

 animal and vegetable oils have to be heated to a boil before 

 they will take fire. But for all this, petroleum and its tribe 

 are less capable — or we might say incapable — of spontane- 

 ous combustion. If exposed to the air in their films they 

 undergo, practically speaking, no immediate chemical change. 

 Hence cotton-waste saturated with such oils will not ignite 

 spontaneous!}', ready as it is to blaze up on contact with a 

 spark. Petroleum has its faults, but there is no need to 

 accuse it of imaginary sins. 



Of all textile fibres silk is the least liable to chemical 

 changes. It will not putrify or decay ; it can be made to 

 burn only with great difficulty, and it is, as furnished us by 

 Nature, utterly incapable of spontaneous combustion. It is 

 very little disposed to condense upon its surface and to 

 absorb gases and vapours, and to take up smells. Hence it 

 is the safest material for the dress of persons exposed to 

 infections. Hut these properties joined to its low conduc- 

 tive power for heat and electricity — the very properties, in 

 short, which render it precious — are now systematically 

 destroyed at the instance of modern greed and the out- 

 cry for cheapness. There has sprung up a practice 

 known as "loading" or "weighting." The depraved 

 ingenuity of the dyers has succeeded in converting a 

 pound of silk into two or even three pounds of a some- 

 thing which possesses none of the properties of silk, 

 chemical or physical, but which may at any rate be sold as 

 silk to the loss of the consumer. Now these weighted silks 

 are decidedly capable of spontaneous combustion. Some- 

 times they have been known to break out into ordinary open 

 combustion. Sometimes they have been known to smoulder 

 away to ashes without any visible fire. In a case of this 

 kind an insurance company was compelled by a French 

 Court — most unjustly, in our opinion — to pay the sum 

 claimed by a warehouseman who held an ordinary fire- 

 policy. We should advise all insurers, railway companies, 

 ship-owners, etc., to be on their guard against this very 

 unsafe material. 



Fires may also be produced if strong acids — in particular 

 nitric and sulphuric — happen to leak out upon straw, 

 saw-dust, hay, or the like. These acids are generally con- 

 veyed in carboys packed in hampers, and hence they rank 

 among the many substances much better adapted for water- 

 carriage than for conveyance by rail. 



In a few instances premises have been set on fire by 

 articles capable of acting as burning-glasses, and thought- 

 lessly left where they might bring the sun's rays to a focus 

 upon some readibly inflammable matter. Decanters filled 

 with water, if made of very clear glass and of a form ap- 

 proaching the globular, can thus act as convex lenses. It 

 is true that in England clear, prolonged sunshine is not so 

 common as to bring this source of danger to the front. In 

 the sunny regions of Australia, South Africa, etc., there is 

 a much greater chance of accidents of this kind. 



Panes of glass with convex knots in them were at one 

 time commonly used for the windows of sheds, out-houses, 

 workshops, etc., and such may still be seen in old buildings. 

 We have seen a piece of blackened paper ignited in the 

 focus of one of these knots, whence they must evidently be 

 set down as dangerous. At the present low prices of glass 

 there can be no reason for their use. 



Another cause of mysterious fires is of a more sudden 

 and perplexing nature. Every one knows that a chip of 

 wood will not take fire at the heat of boiling water — 212^' 

 Fahrenheit. It must either be heated very much higher or 

 be brought in contact with a flame. But if wood is exposed 

 for a long time to the temperature of boiling water it 

 gradually undergoes a series of changes which render it 



much more readily inflammable. It may, indeed, in such 

 cases ultimately take fire without the approach of a flame. 

 What length of time is required to bring about these 

 changes has not hitherto been satisfactorily determined, 

 but it is probably one of months, if not years. Nor are 

 we able to lay our hands upon any precise answer to the 

 question whether a continuous or an intermittent heat is 

 most likely to bring on this result. Alarms of fire, we 

 understand, have occasionally been raised in churches, mu- 

 seums, libraries, and other places heated by means of hot- 

 water pipes, and in other instances, on repairing such 

 buildings, wood work which had been in immediate contact 

 with the pipes was found to be much altered in appear- 

 ance and texture, and to have been rendered very easily in- 

 flammable. 



A few practical precautions are therefore necessary in 

 laying down systems of heating pipes. The metal should 

 rest not upon wood but upon a bed of glass-wool, asbestos, 

 or similar material placed on a slab of stone or stoneware. 

 Above all, no sawdust, shavings, or chips should be left 

 near the piping. 



It is scarcely necessary to say that steam and hot-air 

 pipes present exactly the same risks and require the 

 same precautions. 



The reader will naturally ask whether the forest fires 

 which cause such devastation in semi-tropical countries may 

 ever be due to spontaneous chemical action, fostered by in- 

 tense and prolonged heat ? As" a rule these calamities do 

 not happen " without hands." A traveller drops a match, 

 not caring or not knowing whether it is extinguished or 

 not. It happens to fall upon some dry moss, or some 

 withered and perhaps resinous twigs of underbrush, and 

 the thing is done ! 



Still, if this is the coininon, we suspect it is not the ex- 

 clusive history of the birth of a bush fire. Water placed 

 in a blackened vessel, behind - which is fi.xed a reflector, 

 may be raised to the simmering point on exposure to an 

 Australian sun. Now it seems to us probable that mosses 

 and other finely-divided vegetable matter may, after being 

 thus exposed day by day to the sun, be gradually brought 

 into that state of ready inflammability of which we have 

 just spoken in the case of woodwork in contact with hot- 

 water pipes. Of course, the conditions for such an accident 

 may very rarely coincide. It is only when suitable 

 materials are collected together in sufficient quantity and 

 lie fully open to the sun and screened from the wind that 

 the heat of the mass can rise to the ignition point. But 

 judging from what is known, given these possible con- 

 ditions, the result is, at least, possible. To prove a 

 negative by demonstrating in any particular case that 

 no person could have dropped a match is, of course, im- 

 possible. 



It would be interesting to make an experiment in some 

 place where no harm could accrue, and carefully note the 

 rise of the thermometer and the other phenomena pro- 

 duced. 



It would take us too far were we to enumerate all the 

 substances which may possibly take fire spontaneously, 

 with or without explosion. We will only mention one 

 class of such bodies — the mixtures for coloured fires as 

 used by pyrotechnists. Some of these, if prepared in 

 quantity and kept in stock for some time, have been known 

 to become ignited. Hence, follows the practical conclusion 

 that fireworks should not be manufactured or even stored in 

 quantity in any building situated near to dwelling-houses or 

 to public thoroughfares. It is not pleasant to reflect that 

 your property and your person may at any moment be 

 placed in jeopardy by a slight oversight on the part of a 

 neighbour. 



