Chemistry, inorganic and organic : with experiments / by Charles Loudon Bloxam.
- Charles Bloxam
- Date:
- 1875
Licence: Public Domain Mark
Credit: Chemistry, inorganic and organic : with experiments / by Charles Loudon Bloxam. Source: Wellcome Collection.
651/708 page 623
![compound. Suppose, for instance, that the formation of quinine is to be accounted for— 20CO, + 911,0 + 2NH3 = C,„H,,N,0, + 0,/. Quinine. If sulpbur be a constituent of the vegetable compound to be formed, it is conceivable that the sulphuric acid derived from the sulphates pre- sent in the soil sbould co-operate with th.e carbonic acid, water, and am- monia. If the composition of gluten be correctly represented by the formula ^los'HjcoN'jyOj^S, the equation explaining its formation from the above con- stituents of the food of the plant would be written — 108CO, + UK,0 + 27NH3 -f- SO3 = C„,H,,,N,,03,S -f- 0,^. The cbemical tendency of vegetables, therefore, is to reduce to a lower state of oxidation the substances presented in their food, whilst animals exhibit a reciprocal tendency to oxidise the materials on which they feed. With respect to the last stage in tbe existence of the plant, the ripening of the fruit, we know a little more concerning the cbemical changes which it involves. Most fruits, in their unripe condition, contain cellulose, starch, and some one or more vegetable acids, such as malic, citric, tartaric, and tannic, the latter being almost invariably present, and causing the pecu- liar roughness and astringency of the unripe fruit. The characteristic constituent of unripe fruits, however, is a compound of carbon, hydrogen, and oxygen, the composition of which bas not been exactly determined. Pectose is quite insoluble in water, but during the ripening of the fruit it undergoes a change induced by the vegetable acids, and is converted into pectine (G.^.^'H^o^.^), which is capable of dissolving in water, and yields a viscous solution. As the maturation proceeds, the pectine itself is transformed into pectic acid (CjgHsaOjj), and peciosic acid which are soluble in boiling water, yielding solutions which gelatinise on cooling. It is from the presence of these acids, therefore, that many ripe fruits are so easily convertible into jellies. Whilst the fruit remains green, its relation to the atmosphere a])pears to be the same as that of the leaves, for it absorbs carbonic acid, and evolves oxygen; but when it fairly begins to ripen, oxygen is absorbed from the air, and carbonic acid is evolved, whilst the starch and cellulose are converted into sugar, under the influence of the vegetable acids (page 494), and the fruit becomes sweet. It has been already seen that the con- version of starch and cellulose (CoHi„Or,) into sugar (C„Hi.,0„j would simply require the assimilation of the elements of water, so that the absorption of oxygen and evolution of carbonic acid are probably necessary for the con- version of the tannic and other acids into sugar. For example— CAO„ + 1\0 + = 2C„H,20„ -1- 15C0, Tannic acid. rniit-sugar. 3CJT,Pfl -1- O3 = C„llj,p„ + 3H,0 -I- 6C0,. Tartaric acid. When the sugar has reached the maximum, the ripening is completed • and if the fruit be kept longer, tlie oxidation takes the form of ordinary decay. The scheme of natural chemistry would not be complete unless provi-](https://iiif.wellcomecollection.org/image/b21497382_0651.jp2/full/800%2C/0/default.jpg)
