Eremacausis (Gr. gentle, andcombustion), a term applied by Liebig to the gradual oxidation or slow combustion of organic compounds, vegetable and animal, which takes place in the presence of atmospheric oxygen and water. It is allied to fermentation and putrefaction, and is convertible into the latter by limiting the access of air. Eremacausis is accompanied by the evolution of heat, which is generally only slightly manifested in consequence of the slowness of chemical action. When, however, large masses are undergoing decay, sufficient heat may be developed to create active combustion. The temperature most conducive to eremacausis is about 600 F., and never below 32°. Moisture is a necessary condition, perfect dryness always completely arresting the process. Light is often produced by eremacausis in the form of phosphorescence, a phenomenon observed in decaying stumps and trunks of trees, and in animal flesh under favorable conditions. The explanation of this is still a matter of doubt, although modern science offers a solution in the fact that molecular vibrations may be created which are capable of communicating undulations of light unaccompanied by those of heat.
The chemistry of eremacausis was carefully studied by Liebig several years ago, and although some of his views have been somewhat modified, they form with the investigations of De Saussure the basis of most of the knowledge we have upon the subject. The decay of wood is the most familiar example of the process, in which the hydrogen of the wood becomes more rapidly oxidized than its carbon, causing the formation of a brown powder called humus or ulmine, a substance which contains a much greater proportion of carbon than woody fibre. The action of oxygen on organic bodies at common temperatures and with free access of air is somewhat analogous to that which obtains when the temperature is raised with limited access of air. It is well known that in the latter case the oxygen unites with other elements than the carbon; also that the oxygen, hydrogen, and whatever nitrogen may be contained in the organic body, separate to a certain extent from the carbon and form new compounds, leaving a portion or nearly the whole of it in a free state, as in the manufacture of charcoal, and the production of coke in the retorts of gas works.
In eremacausis, however, there is a union of carbon and oxygen, forming carbonic acid, and also of hydrogen and oxygen, forming water; but the latter process being much more rapid, the remaining portion of the decomposing body becomes richer in carbon, and gradually converted into humus, which substance continues to oxidize, becoming at last completely converted into carbonic acid and water. The nitrogen of the organic body passes into ammonia and into nitrous and nitric acids, and it is supposed that there is also a portion of atmospheric nitrogen absorbed and converted into the same substances. When nitric acid is formed it combines with the alkaline and earthy constituents of the vegetable juices, forming nitrates. According to Kuhl-mann, ammonia may also be transformed into nitric acid when the access of air is small; and in this way the nitre in the caves of Zeilan and in the grottoes on the banks of the Seine, and also in cellars, has been accounted for. Fungi are plentifully developed during slow decay, appropriating considerable nitrogen, often more than is contained in the decaying body, but whether directly from the air or through the intervention of other chemical processes, which is probable, is uncertain.
Whatever combination takes place between the carbon of the decaying body and the oxygen of the air is also probably not direct, the gas being first absorbed by moisture, and then delivered to the elective affinity of the constituents of the woody fibre. Eremacausis is retarded or completely arrested by all those substances which prevent fermentation or putrefaction, such as creosote, carbolic acid, the mineral acids, and salts of mercury, copper, and other metals. Pasteur, who contends that fermentation and putrefaction are processes carried on by living organisms, adduces a number of experiments which he regards as proving that eremacausis also never takes place except by the influence of certain lower organisms.