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case 4 eqs. of oxygen (See Example 12). Along with this analogy in composition, there is, as we see, a marked analogy of properties, and as we rise in the scale, the physical characters vary regularly as the amount of CH increases. Every addition of C, H, raises the fusing and boiling points 19 degrees. This applies to the boiling points in all the other columns, as far as known.

EXAMPLE 12 Volatile Oily Acids of the Series (C, H,), 04. Formic Acid = C, H, 0,

Enanthylic Acid = Acetic = c no

Caprylic Propylic = c H o

Pelargonic Butyric = c H o

Capric Valerianic

Margaritic Caproic =

Laurostearic Cocinic Acid =

Margaric Myristic

Bassic
Benic
= Cso H3, o

Balenic
Ethalic
Behenic Acid=C,, H,, 0,

Cerotic Acid=C5, H5, 0, Melissic Acid=C., H., 04: Derivation of the above Acids from Sugar by Deoxidation. Sugar, C, H,, 0,2-0, = C, H, O, = Caproic Acid. 2 eqs. of Sugar, C24 H,4 0,4--012=3(C, H, 0,) = Butyric Acid. 2 eqs. of Sugar, c,H,4 021-02,= C., H,,0 = Laurostearic Acid. 5 eqs. of Sugar, Co H.. 06-05:=2(C3, H3, 0,) = Benic Acid. 5 eqs. of Sugar, Coo Hoo 030-056= C, H, O, = Melissic Acid.

While on these volatile acids, I may mention that they may be formed, according to Liebig, in the animal body in two ways, by the deoxidation of starch or sugar, or by a process of fermentation. The most recent researches tend to establish this doctrine; for if we compare the composition of sugar (sugar of milk or cane sugar + 1 eq. water) with that of these acids, we see that they differ in oxygen alone. Sugar is C12 H, 01, and caproic acid is C12H12 0, 2 eqs. of sugar, C., 112, 0, 4 yield 3 eqs. of butyric acid (C, H, 0), and 02, or 1 eq. of Laurostearic acid, and 20 of oxygen. Lastly, taking the acids higher in the list, 5 eqs. of sugar yield either 2 cqs. of benic acid and 52 eqs. of oxygen, or 1 eq. of melissic acid and 56 of oxygen. (See Ex. 12.) Now this last acid is formed by the bee from sugar, being found in wax. Caproic acid is found in butter, and butyric acid also, as well as caprylic acid. Capric acid is found in goat's fat, and, I believe, goat's butter. Moreover, we can produce, artificially, from sugar, formic acid, acetic acid, propylic acid, and butyric acid, and I have no doubt we shall produce in time the whole of them. Amylic alcohol, the alcohol of valerianic acid, is formed in the fermentation of starch sugar, as is also capric acid, and probably margaric acid. I have found valerianic acid in old plum jam and in butter.

It is well known that in all fats and fat oils, these and other oily acids are combined with glycerine; but the composition of glycerine is also very close to that of sugar, from which it differs in containing a little more hydrogen and a little less oxygen, so that it also may be derived from sugar by deoxidation.

The next, the 7th column, contains the ammonia salts of the acids, all of which are known; and in the 8th column are given the compounds called nitryles, derived from these ammonia salts by the removal of 4 eqs. of water. It will be seen by the 9th column that the composition of the nitryle, belonging to any radical, is the same as that of the cyanide of the radical next below it in the scale. Several nitryles are known, and some of them are the cyanides of the next radical below; others appear to be isomeric only with the cyanides.

The next, the 10th, column gives the chlorides of the radicals; the next the sulphurets; and the next the compounds of the sulphurets, with sulphuretted

hydrogen. Of all these, several are known. The latter represent the alcohols, in which 0, is replaced by S., and mercaptan is the type of them. They are horribly fetid, combining the most offensive odours of assafetida, garlic, onions, leeks, &c., in unparalleled variety and intensity.

The two last columns give, first, the compounds of each radical with amide or ammonia, minus hydrogen; and secondly, the same arranged empirically, as the results of analysis. These bodies are all, so far as known, bases, probably all volatile bases, oily below, crystalline higher up; and those lowest in the list, discovered about a year ago by Wurtz,-are so analogous to ammonia that they may readily be confounded with it. Their empirical formulæ, as given in the last column, hardly show this analogy; but let us consider each as NĚz, in which H is replaced by a radical, and the analogy in constitution comes out. This is seen in the previous column, for we may consider ammonia as NH,+H; methylamine as NH, + C, H,; ethylamine as NH, + C, H,, and so on. I shall have to return to these bases.

This table illustrates the advantage of symbols; for if we have the first horizontal line, containing one radical and its derivatives (and the table as it stands does not contain one-half of those known of the radical ethyle, for example), we can then construct the whole table by successive additions of C, H, in every vertical column. And as in one column, that of the acids, the recent progress of chemistry has enabled us to fill in more than 20 of the series, while in all the others several members are known, and new ones are daily added, we cannot doubt that the principle on which it is founded is a natural law.

Nor is this a solitary instance of the principle of homologous compounds. The benzoic acid (Example 13) belongs to another such series, of which four or five members are known, and there also the common difference is C, H,. There also a series of volatile bases is known, of which aniline is the type, and which closely resemble certain natural bases. These bases are derived, by substitution, from the carbo-hydrogens in the middle column.

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Of late years, much light has been thrown on the formation of organic compounds in plants and animals by the study of the metamorphoses or transformations of organic substances. It is evident that, considering the high atomic weight and complex molecules of these bodies, and bearing in mind also that a change in the arrangement of the particles may cause a change of properties, as well as an alteration of their proportion, organic compounds must be especially liable to such transformations. Some of these have long been familiar, as the change of starch into grape sugar, that of sugar into alcohol and carbonic acid, that of cyanate of ammonia into urea, and that of oil of bitter almonds into benzoine. In these cases, nothing is added, and nothing removed; but a new arrangement, more stable under the circumstances, is effected. There are now many other examples, some of which I shall have to mention hereafter. But there is another very common kind of transformation where some compound, such as ammonia, is added. Here the only difference is, that the particles newly arranged, were not previously combined in one conipound, but undergo the change when brought together. Examples of this are found in the formation of many amides, such as oxamide, and such bodies as murexide. (This was illustrated by the instantaneous formation of these bodies.) A third and most important class of transformations is that effected by heat or destructive distillation, the products of which, especially when nitrogen is present, are singularly varied, and are daily becoming better known. Fermentations belong chiefly to the first class of transformations. Putrefaction is a kind of fermentation, where oxygen is excluded or but sparingly admitted after the process has begun; and decay is a transformation under the influence of oxygen, yielding, for the most part, the ultimate products, carbonic acid, water, and ammonia.

The newest and best definition of putrefaction and fermentation is that of Liebig. A putrescible body is one generally, perhaps always, nitrogenised, which, in contact with air, moisture, and a certain temperature, undergoes a spontaneous decomposition. It is then putrescent or a ferment. A fermentiscible body is one which, by itself or in solution in water, does not undergo any decomposition ; but when in contact with a putrescent body, is resolved into new products, and then is in a state of fermentation. As fermentation is produced by the communication of motion from the atoms, not the molecules, of the putrescent body to the atoms of the fermentescible one, the process requires time, and is not instantaneous, like a common precipitation; and as putrefaction is itself propagated in the same way, so it also is a slow process. Moreover, as the ferment can only act as long as its atoms are in motion, its power to cause fermentation must cease as soon as its own decomposition is complete, and not before. Hence a given weight of ferment can only cause the fermentation of a limited quantity of sugar or other fermentescible bodies.

One very striking result of the progress of our knowledge in regard to the points I have briefly alluded to is this, that we daily acquire in a greater degree the power of artificially imitating the natural processes in plants and animals, and of thus producing organic compounds, very often entirely analogous to natural products, and sometimes identical with them. It is evident that nothing can so well prove our real progress as this, and I shall, therefore, dwell on it a little, since it forms the peculiar feature of the present state of the science, and holds out the greatest prospect of future and still greater progress.

I would point out, first, that the natural process in vegetables is distinct from, and indeed opposed to, that which goes on in the animal body. In plants, their food consists of the least complex compounds ; of carbonic acid, water, ammonia, sulphuric acid, and the mineral salts found in their ashes. Now, under the influence of light, the plant exerts a prodigious power of deoxidation, insomuch that in the formation of cellulose or woody fibre, from 12 eqs. of CO, and 8 eqs. of HO, a quantity of oxygen is separated and sent into the atmosphere equal to that contained in the CO,,—that is, 24 eqs. of O from the above quantities. The same thing occurs in sugar, starch, and gum, only that the amount of HO is larger. Between co, and HO, the food of plants and cellulose, &c., in forming which all the oxygen of the carbonic acid is separated,—we have a long list of compounds intermediate in amount of oxygen, such as (see Example 14) oxalic, malic, citric and tartaric acids, &c.; and on the other side of cellulose, &c., we have a long list of bodies with less oxygen than starch or sugar, namely, the fat or fixed oils, the essential oils and the resins. Taking the whole process, from CO, + HO to oil of turpentine C, H, or C2, H16, we have a continuous deoxidation, a process of reduction. But this process lias another and a still more important character, namely, that from less complex molecules more complex are built up or constructed. It would appear that this can only, or most easily and effectually, be effected by aid of a deoxidising or reducing process.

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