WOOD, Rotten, Illumination of. This is a subject which has often been discussed by naturalists. Spallanzani maintained, that there is a perfect analogy between the illumination of rotten wood, and artificial phosphorus; and he imagines, that in the putrid fermentation, the hydrogen and the carbone of the wood come more easily in contact with the oxygen of the atmosphere, by which combination a slow combustion, and the illumination of the wood, is produced; and he thinks that this process cannot proceed in the irrespirable kinds of gases. Rotten wood also, in which the necessary quantity of hydrogen and carbone is not at the same time disengaged, does not obtain the property of illuminating. Mr Corradori, however, objects to this
theory, that the slow combustion does not take place according to the above theory, as the wood, at the time when it begins to illuminate, is mostly deprived of its resinous particles, and consequently contains but very little hydrogen and carbone; and it appears to him more probable, that the more it loses of combustible matter, the more it obtains the property of illuminating. There is, he thinks, a very great difference between this natural and the artificial phosphorus. Mr Humboldt concludes, from his experiments, that the illumination of rotten wood takes place only when it gets into contact with oxygen; and when it has lost the property of emitting light in irrespirable gases, it recovers it again by exposing it to oxygen gas. Dr Gartner, however, is of opinion, that, according to his experiments, a certain degree of humidity is always requisite, and he thinks that oxygen gas is not quite necessary though the illumination be increased by it. This phenomenon, however, being so very different from all known processes of combustion, where light is disengaged, Dr Gartner asks, whether it be not more agreeing with the animal process of respiration, than with a true combustion, or whether the illumination of the wood be produced by phosphorus and carbone in a proportion hitherto unknown. Dr Gartner is, on the whole, inclined to think, that it is at present impossible to give a satisfactory explanation of all the phenomena that occur in this process. Beckmann has made numerous experiments on the illumination of rotten wood, in different gases and fluids, in order to throw some light on the ideas of the above naturalists. The results of these experiments differ in some points from what the experiments of those gentlemen have shewn, which, however, Beckmann ascribes to the nature of rotten wood, as a substance that is not always of the same kind, and has not always an equal degree of putrefaction and humidity. It seems also to differ materially from the artificial phosphorus in the following particulars. 1. It shines in oxygen gas at a very low temperature. 2. It emits light in all irrespirable gases, at least for a short time. 3. In muriatic acid gas its light is suddenly extinguished. 4. It shines in a less degree in air rarefied by the air-pump. 5. According to Mr Corradori, it even shines in the torricellian vacuum. 6. Its illumination is extinguished in oxygen gas, as well as in other kinds of gases, when they are heated. 7. By its illumination in oxygen gas, carbonic acid gas is produced. 8. One may suffer the rotten wood to be extinguished several times, one after another, in irrespirable gases, without depriving them of the property of making new pieces of rotten wood shine again. 9. Humidity greatly promotes the illumination, and even seems to be necessary in producing it. 10. The rotten wood continues to shine under water, oil, and other fluids, and in some of them its light is even increased. All this seems to shew, that the extinction of rotten wood, in different media, does not immediately depend on a want of oxygen, but rather on a particular change, to which the wood itself has been exposed.