« PreviousContinue »
culiar principles ; but it would exceed the bounds of this work to describe them all in detail. The chief among them are suber, or a peculiar substance found in cork; asparagin, found in asparagus; medulling from the pith of the sunflower ; fungin, the fleshy part of mushrooms, &c.
Vegetables also contain several acids ready formed. Vegetable and animal acids differ from the others essentially. They always contain carbon and hydrogen: some of them contain azote, and generally, though perhaps not always, oxygen. They do not seem capable of combining with different proportions of oxygen only, but whenever the quantity of this principle changes, that of the rest changes also.
Tartaric acid. Tartar, or cream of tartar, is a · substance found in an impure state, incrusted on the bottom and sides of wine casks : when purified by solution and filtration, it is sold for use. This salt, which is soluble in water, consists of tartaric acid and potash ; it is therefore tartrate of potash. Tartaric acid when crystallized is imperfectly transparent, white, and does not deliquesce in the air. It is soluble in water. It combines with alcalies, earths, and metallic oxides, and forms tartrates.
Oxalic acid, so called from being first obtained from oxalis acitosella, or wood-sorrell. It is also called the acid of sugar, because obtained from sugar by the nitric acid. It is
It is proper that every one should know that oxalic acid is a deadly poison, and that many persons have lost their lives by mistaking it for Epsom salts, which it resembles. It is much employed for cleaning boot-tops and leather, and also by the calico-printers.
Malic acid was first found in the juice of apples. It exists also in many other vegetables. This acid
is very sour, and does not crystallize; it forms salts with many of the metallic oxides.
Gallic acid. - This acid is found in gall-nuts. It crystallizes, and forms whitish crystals, of a sour taste and peculiar smell. When gallic acid is put into a solution containing iron, a black precipitate appears. The base of ink is iron thus precipitated. To produce good black ink, infuse one pound of powdered gall-nuts for four hours, without boiling, in common water, with six ounces of gum-arabic, and six ounces of sulphate of iron. With gold, gallic acid forms a brown precipitate; with silver, 4 grey; with mercury, an orange; with copper, a brown; and with lead, a white,
Citric acid is procured from the juice of lemons and other fruits. It is capable of crystallizing. Its erystals are soluble in water, and very sour. forms citrates with the earths, alkalies, and metals. It is much ụsed in calico-printing. It is also used for discharging spots of ink from linen.
Benzoic acid is obtained from gụm-benzoin, or benjamin. It is a crystallizable acid. The compounds which it forms are called benzoates.
Kinic acid is found in Peruvian bark.
If mucilaginous saccharine vegetable substances be subjected to the action of water and heat, (from 60 to 70 deg. Fahr.) they experience, in a very short time, a very striking change. An internal commotion takes place, the mass grows turbid, a large quantity of air-bubbles, consisting of carbonic acid gas, are disengaged, which, on account of the viscidity of the matter in which they are inclosed, form a stratum on the surface of the fluid, known
by the name of yeast. After a time these appearances cease; the fermented liquor becomes clear and transparent, and no more gas is discharged. The liquor now has lost its sweetness and viscidity, and has acquired the vinous taste and intoxicating quality. Sugar appears to be essential to this process; and all mucilaginous substances containing sugar are capable of this fermentation, which is called the vinoús.
Wine is made in this manner from the juice of the grape; if the fermentation be checked when at its height, by excluding the air, the wine begins to ferment anew, and effervesces when again exposed to the air. The sparkling wines, as Champagné, are prepared in this manner, and hence should be considered as imperfect wines. Το
prepare vinous liquors from grain or corn, it must first be converted into malt, by steeping it in water, and then exposing it to the air, turning it frequently over ; by this process, the gluten of which the germ consists is separated, and the fecula is converted into sugar by the germination of the seed.
Beer is made by boiling the malt in water, which produces a sweet liquor called wort; this is converted into beer by fermentation and the addition of hops, which furnish a bitter substance.
Wine, beer, and all ferimented liquors, owe their intoxicating qualities to a peculiar substànce which they contain, and which is the produce of fermentation alone. This substance is a fluid called alko . hol, or spirit of wine, and may be separated in a pure state by distillation. When first obtained it is mixed with a quantity of water, but if it be redistilled, it is obtained very pure, and is then called rectified alkohol; Alkohol is of a strong heating
taste, of a peculiar penetrating odour, and it is very
inflammable and volatile. It dissolves resins, essential oils, camphor, sulphur, phosphorus, &c. It is composed of hydrogen, carbon, and a small quantity of oxygen.
Strong acids and alkohol have a considerable action on each other, and this produces ether, which is a fluid still more highly volatile, inflammable, and odorous. Nitric acid with alkohol produces nitric ether, and sulphuric acid in the same way produces sulphuric ether.
When wine, or any fermented or vinous liquor is exposed to a heat, from 75° to 859 Fahr., and access of air is permitted, the fluid becomes turbid, and a new change of principles takes place. It loses its taste and smell, it becomes sour, and is converted into vinegar, or acetous acid. Though vinegar is chiefly prepared from fluids which have undergone the vinous fermentation, yet this is not necessary to the production of vinegar, for simple mucilage is capable of passing into the state of acetous fermentation. When the saccharine principle predominates in any substance exposed to the necessary conditions of fermentation, alkohol is produced; when mucilage is most abundant, vinegar or acetous acid is the product; and when gluten is predominant, ammonia will be discovered, and putrefaction will take place.
Common vinegar may be purified, or concen trated by distillation, and it is then called distilled vinegar. This, however, still consists of the acetic acid and water. To free the acid from the water, distilled vinegar is saturated with some metallic oxide, and an acetate is thus formed. The acetate is then heated red hot in a retort, by which it is decomposed, and the acetic acid passes over pure.
Acetate of copper or verdigris, and likewise acetate of lead, are used for this purpose. Acetic acid is very pungent and caustic. It is tile, and combines with the metals, earths, and alkalies.
This acid may also be obtained from wood, by subjecting it to distillation in a retort. In this state it is very impure, being combined with a quantity of empyreumatic oil. This was formerly called pyroligneous acid. When separated from impurities it is essentially the same with vinegar, and is now employed for the same purpose.
The last change, or final decomposition that vegetables undergo, is called the putrefactive fermentation, or putrefaction. Without moisture, heat, and a due access of air, this does not take place. By this vegetables are resolved into their constituent principles, and ammonia is formed.
The elementary principles of animal substances are nearly the same with those of vegetables, but the former contain more nitrogen and phosphorus, and the latter more carbon and hydrogen.
The proximate constituent parts of animal substances are the following:
Gelatine, or animal jelly, is very generally dispersed through all the parts of animals, even in bones, but exists in the greatest quantity in the tendons, membranes, and the skin. It is a viscid substance, very soluble in warm water, but not in alkohol; insipid, and without smell; when cold, it congeals into a cohesive, tremulous substance. It forms the basis of soups, broths, &c. and imparts to