Chap. VII Of the Putrid Fermentation of Vegetable Substances
Process I.
The Putrefaction of Vegetables.
Fill a hogshead with green plants, and tread them down a little; or, if the vegetables be dry and hard substances, divide them into minute parts, and steep them a little in water to moisten them: then leave them, or the green plants, in the vessel, uncovered and exposed to the open air. By degrees a heat will arise in the center of the vessel, which will continue increasing daily, at last grow very strong, and be communicated to the whole mass. As long as the heat is moderate, the plants will retain their natural smell and taste. As the heat increases, both these will gradually alter, and at last become very disagreeable, much like those of putrid animal substances. The plants will then be tender as if they had been boiled; or even be reduced to a kind of pap, more or less liquid according to the quantity of moisture they contained before.
OBSERVATIONS.
Almost all vegetable matters are susceptible of putrefaction; but some of them rot sooner, and others more slowly. As putrefaction is only a species of fermentation, the effect whereof is to change entirely the state of the Acid, by combining it with a portion of the earth and Oil of the mixt, which are so attenuated that from this union there results a new saline substance in which no Acid is discernible; which on the contrary hath the properties of an Alkali, but rendered Volatile; it is plain, that, the nearer the Acid of a plant set to putrefy is to this state, the sooner will the putrefaction of that plant be completed. Accordingly all plants that contain a Volatile Alkali ready formed, or from which it can be obtained by distillation, are the most disposed to putrefaction.
Those plants, in which the Acid is very manifest and sensible, are less apt to putrefy; because all their Acid must undergo the change above specified. But vegetable matters, whose Acid is entangled and clogged by several of their other principles, must be still longer elaborated, before they can be reduced to the condition into which complete putrefaction brings all vegetables. The earthy and oily parts, in which the Acids of these substances are sheathed, must be attenuated and divided by a previous fermentation, which, from those parts subtilized and united with the Acid, forms an Ardent Spirit, wherein the Acid is more perceptible than in the almost insipid, or saccharine juices, out of which it is produced. The Acid contained in the Ardent Spirit must be still further disengaged, before it can enter into the combination of a Volatile Alkali: consequently the Ardent Spirit must undergo a sort of decomposition; its Acid must be rendered more sensible, and be brought to the same condition as the Acid of plants in which it manifests all its properties.
Hence it appears, that the spirituous and acetous fermentations are only preparatives, which nature makes use of, for bringing certain vegetable matters to putrefaction. These fermentations therefore must be considered as advances towards that putrefaction, in which they terminate, or rather as the first stages of putrefaction itself. This is the opinion of Mr. Stahl, who hath treated this subject with great sagacity, and thrown much light upon it.
Mr. Boerhaave is not altogether of the same mind. He considers putrefaction as something foreign to fermentation; as an operation independent of it, and very different from it. He gives the title of fermentation to that intestine and spontaneous motion only which produces an Ardent Spirit, and changes it into an Acid. He founds his opinion on this, that the circumstances attending putrefaction are different from those which accompany spirituous and acetous fermentation; that the product of putrefaction is very different from the products of these fermentations; and lastly, that all vegetable and animal substances are susceptible of putrefaction, whereas only some kinds of them are capable of fermentation properly so called.
Mr. Boerhaave is so far right, that we ought not to confound together operations which differ in several respects, and result in different productions; but Mr. Stahl’s opinion must nevertheless be looked on as highly probable, or rather absolutely true. For it doth not necessarily follow, from the difference between the circumstances and productions of fermentative motions, that the operations have no relation to, or connection with, each other. They may nevertheless be considered as different steps of one and the same operation: and if all vegetable and animal matters are not susceptible of the three degrees of fermentation, we can only infer from thence that there are mixts, in which the whole work of fermentation is yet to do; and that there are others whose principles are so disposed that they are in the same condition as if they had already undergone the first, or even the second, degree of fermentation; and consequently such mixts are susceptible only of the second, or perhaps of the third, degree of fermentation.
Mr. Stahl therefore says very judiciously, that, far from denying putrefaction to be a fermentation, we ought on the contrary to consider all fermentation as no other than putrefaction. Matters susceptible of the spirituous and acetous fermentation do but pass through these previous alterations in their way to complete putrefaction. On this principle, Wine and Vinegar are only liquors that had begun to putrefy, but were stopt at the first or second stage of their putrefaction. This is so true, that, if a fermenting liquor be left to itself in the open air, and in a due degree of heat, it will proceed directly, without any stop, to perfect putrefaction.
The acetous fermentation is attended with more heat than the spirituous, and the putrid with still more than the acetous. The heat of putrefying plants is sometimes so considerable, that, when they are not too moist, and are stacked up in great heaps, they take fire and burn violently. Of this there are frequent instances in hay-ricks.
Process II
Putrefied Vegetable Substances analyzed.
Put the putrefied plants you mean to analyze into a glass cucurbit, and set it in a sand-bath. Fit to it a head; lute on a receiver; distil with a gentle fire, and a limpid fetid liquor will come over. Continue the distillation till the matter contained in the retort be almost dry.
Then unlute your vessels, and keep the liquor you find in the receiver by itself. Put the matter remaining in the cucurbit into a retort, and distil with a graduated heat. There will rise white vapours; a pretty considerable quantity of liquor nearly like that of the former distillation; a Volatile Salt in a concrete form; and a black oil, which towards the end will be very thick. In the retort there will remain a black charred matter, which being burnt in the open air will fall into ashes, from which no Fixed Alkali can be extracted.
By means of a funnel separate your oil from the aqueous liquor. Distil this liquor with a gentle heat. You will by this means obtain a Volatile Salt like that of animals; of which you may also get some, by the same means, from the liquor which came over in the first distillation.
OBSERVATIONS.
This analysis shews the changes which putrefaction produces in vegetable matters. Scarce any of their principles are now to be discerned. They now yield no aromatic liquor; no Essential Oil; no Acid; and consequently no Essential Salt, Ardent Spirit, or Fixed Alkali: in a word, whatever their natures were before putrefaction, they are all alike when they have once undergone this fermentative motion in its full extent. Nothing can then be obtained from them but Phlegm, a Volatile Alkali, a fetid Oil, and an insipid Earth.
Almost all these changes are owing to the transmutation of the Acid, which is depraved by putrefaction, and combined with a portion of the Oil and subtilized Earth of the mixt; so that the result of their union is a Volatile Alkali. Now, as the Fixed Alkali, found in the ashes of unputrefied plants, is only the most fixed part of their earth and of their Acid, closely united together by the igneous motion, it is not surprising that, when all the Acid, with a part of the earth, is subtilized and volatilized by putrefaction, no Fixed Alkali can be found in the ashes of putrefied Vegetables. The alteration which the Acid suffers by the putrefactive motion is, in my opinion, the greatest it can undergo, without being entirely destroyed and decomposed, so as to be no longer a Salt.
We have seen it, in the Mineral kingdom, in its greatest purity and strength. Its combination with Oil, and the other alterations its undergoes, in the Vegetable kingdom, have shewn it weakened and disguised. The changes it suffers by the spirituous and acetous fermentation, have exhibited it in other forms. And lastly, putrefaction disfigures it completely, and, in some sort, changes its very nature, so that it cannot be distinguished. In the animal kingdom we find it nearly in the same condition: for though the Vegetable substances, on which animals feed, do not undergo direct putrefaction, in its full extent, before they are converted into animal juices, yet they suffer most of the alterations produced by putrefaction; so that when they have acquired the qualities necessary to their becoming an actual nutritious animal juice, they are within one step of complete putrefaction. For this reason all animal substances are very apt to putrefy, and are unsusceptible of the first degrees of fermentation. But this discussion belongs to the animal kingdom, of which we are now going to treat in the third part of these Elements; the theory of putrefaction serving to introduce it, and naturally leading us to it.