Our readers will remember the brief article on this subject on page 134, when our views were requested as to the possibility of charcoal dust taking fire spontaneously, when exposed to moisture. Our opinion was in the negative, and opposed to some scientific men in Philadelphia, who had been consulted on the question. The following is a very useful, practical and able communication relating to this subject : MESSES. EDITORS—It appears that Mr. Blackburn's conclusions (page 134) respecting the origin of the fire in the freight-house in Philadelphia were based upon the opinion of certain scientific men. Now it is a well-known fact to practical men that many of our scientific men are exceedingly ignorant upon some of the most common things in practical life. I will give one instance, and then proceed to my subject. Some nine years ago, some of the French philosophers discovered that the finger or hand could be passed through a stream of liquid iron without being injured by the intense heat. This was a subject of much comment and discussion in scientific publications, both in this country and Europe ; and while they were astonished at the wonderful discovery, it was a thing that had been perfectly familiar to workers in iron since the building of the iron gods spoken of by Daniel the prophet. I have been perfectly familiar with pulverized charcoal and other coal, in connection with the foundry business, for over twenty years, and for the last two years have heen extensively engaged in the manufacture of foundry facings, rectifying coal, &c. I work up nearly twenty thousand bushels of charcoal per annum into dusts of various grades, and these are at times subject to various degrees of dampness, from aqueous absorption from the atmosphere to perfect saturation with water, and in no instance have I ever been able to discover a sensible increase of heat. If there was a chemical affinity between charcoal and oxygen, the result would be the increase of temperature in the mass, and the liberation of hydrogen gas, neither of which takes place with any degree of moisture. A few. facts will set at rest this charcoal question. The ink of charcoal on the parchment taken from the catacombs of Egypt has been found not to have undergone any change ; and the charcoal taken from Herculanseum and Pompeii is the same as coal burnt to-day ; and it is a common practice to char fence posts to prevent oxydation, which is nothing but slow combustion. The rusting of metals, rotting of wood, and decomposition of organic matter are all cases where heat is generated ; but charcoal may be exposed for any length of time without undergoing these changes, and it is well known to be one of the most indestructible materials in nature. Charcoal, Lehigh coal, plumbago, and the diamond are almost the same in chemical properties—all are nearly pure carbon, and all nearly equally unaffected by the action of the weather elements. Now for the probable cause of the fire referred to in Philadelphia. Charcoal has a strong affinity for moisture, and not oxygen, at ordinary temperature. Pulverized merchant charcoal contains about 15 per cent of water, and with this amount of moisture will readily ignite a strong spark. I have known over twenty fires by charcoal dust, and have seen the facing ways used in foundries on fire a hundred times, and in all cases by scintillations thrown off by spilling the molten iron. I know one foundry that has been burnt four times by this means ; and many foundries, for this reason, have given up grinding their coal. What makes this material most dangerous is, it takes fire very easily from a strong spark when fine and dry, but does not show itself for several hours, and sometimes days after. The only safe way of telling when it is on fire, in the early stages, is by feeling it with the hand. It may be full of fire and not perceptible to the eye. I have frequently set charcoal dust on fire by friction in grinding ; and in one case it did not show itself until four and a-half days afterwards. The fire in the bags in the depot at Philadelphia may have been in them when they left the mill, or communicated by a spark from the engine, or from a cigar. Charcoal is one of the best and cheapest non-conductors of heat known, and in my judgment may be used with safety with any amount of moisture, and with equal safety dry, when protected from sparks, and kept at a temperature a little below the melting point of lead. L. A. ORCUTT. Albany, N. Y., February, 1858. [In a recent number of Emery's Journal of Agriculture (Chicago), it quotes our opinion referred to above, and'regards it " as having great weight;" at the same time, it gives the opinion of a practical man in reference to a mode heretofore unknown to us, whereby charcoal dust may be ignited. This gentleman stated that " charcoal long exposed to moisture, and suddenly dried or heated, would ignite. He had known well authenticated instances from such a cause; and of no article about his premises was he more careful than of the disposition of charcoal." This is a question of considerable importance to those who use fine charcoal dust ; and we hope experiments may be made which will prove its liability to accidental combustion, or the reverse. It is important that the facts should be known.—EDS.
This article was originally published with the title "Is Charcoal Liable to Spontaneous Combustion ?" in Scientific American 13, 24, 190 (February 1858)