RADICALS—ACIDS—BASES—NEUTRALS.

In the introduction to these brief chapters upon Chemistry, we said that the science was divided into two sections, the first section consisting of the simple combinations, and the other of compound combinations. The latter being met with chiefly in animal and vegetable matter, as distinguished from dead or inert matter, was termed Organic. This distinction will be seen below.

We have already placed before our readers the elements and their simple combinations, and have incidentally mentioned the decomposition by electricity and by light. In the section upon Electricity the positive and negative poles are explained. Oxygen appears always at the positive pole, potassium at the negative. The other simple bodies vary. Chlorine, in combination with oxygen, is evolved at the negative pole, but when with hydrogen at the positive pole. In the series below each element behaves electro-negatively to those following it, and electro-positively to those above it; and the farther they are apart the stronger their opposite affinities are.

Electrical Relation of the Elements.

• Oxygen.
• Sulphur.
• Nitrogen.
• Chlorine.
• Bromine.
• Iodine.
• Fluorine.
• Phosphorus.
• Arsenic.
• Carbon.
• Chromium.
• Boron.
• Antimony.
• Silicium.
• Gold.
• Platinum.
• Mercury.
• Silver.
• Copper.
• Bismuth.
• Lead.
• Cobalt.
• Nickel.
• Iron.
• Zinc.
• Hydrogen.
• Manganese.
• Aluminium.
• Magnesium.
• Calcium.
• Strontium.
• Barium.
• Sodium.
• Potassium.

The importance of these facts to science is unmistakable, and, indeed, many attempts have been made to explain, from the electrical condition of the elements, the nature of chemical affinity, and of chemical phenomena in general.

Electrotyping is another instance of decomposition by means of electricity, and respecting decomposition by light we know how powerful the action of the sun’s rays are upon plants, and for the evolution of oxygen. The daguerreotype and photographic processes are also instances which we have commented upon. So we can pass directly to the consideration of the compound groups.

In nearly every complex organic compound we have a relatively simple one of great stability, which is termed the radical, which forms, with other bodies, a compound radical.22 In these complex groups we find certain elements generally,—viz., carbon, hydrogen, nitrogen, sulphur, and phosphorus. Some compounds may consist of two of these, but the majority contain three (hydrogen, oxygen, and carbon). Many have four (carbon, oxygen, hydrogen, and nitrogen), and some more than four, including phosphorus and sulphur. Others, again, may contain chlorine and its relatives, arsenic, etc., in addition. Now we will all admit that in any case in which carbon is present in composition with other simple bodies forming an organic body, and if that body be ignited in the air, it burns and leaves (generally) a black mass. This is a sure test of the presence of carbon, and forms an organic compound. Similarly in decomposition nitrogen and sulphur in combination inform us they are present by the odour they give off. We need not go farther into this question of radicals and compound radicals than to state that a compound radical plays the part of an element in combination. We find in alcohol and ether a certain combination termed Ethyl. This “compound radical” occurs in same proportions in ether, chloride of ethyl, iodide of ethyl, etc., as C₂H₅; so it really acts as a simple body or element, though it is a compound of carbon and hydrogen. A simple radical is easily understood; it is an element, like potassium, for instance. We may now pass to the organic combinations classified into Acids, Bases, and Indifferent, or Neutral, Bodies.

I. Acids.

There are several well-known organic acids, which we find in fruits and in plants. They are volatile and non-volatile; acids are sometimes known as “Salts of Hydrogen.” We have a number of acids whose names are familiar to us,—viz., acetic, tartaric, citric, malic, oxalic, tannic, formic, lactic, etc.

Acetic acid (HC₂H₄O₂) is a very important one, and is easily found when vegetable juices, which ferment, are exposed to the air, or when wood and other vegetable matter is subjected to the process of “dry distillation.” Vinegar contains acetic acid, which is distilled from wood, as we shall see presently. Vinegar is made abroad by merely permitting wine to get sour; hence the term Vin-aigre. In England vinegar is made from “wort,” of malt which is fermented for a few days, and then put into casks, the bung-holes of which are left open for several weeks, until the contents have become quite sour. The liquid is then cleared by isinglass. The vinegar of commerce contains about 6 per cent. of pure acetic acid, and some spirit, some colouring matter, and, of course, water. Wood vinegar (pyroligneous acid) is used for pickles. The ordinary vinegar when distilled is called white vinegar, and it may also be obtained from fruits, such as gooseberries or raspberries.

Acetic acid, or “wood vinegar,” is prepared as follows:—There are some large iron cylinders set in brickwork over furnaces, and these cylinders have each a tube leading to a main pipe in which the liquid is received for condensation. The cylinders, which contain about seven or eight hundredweight, are filled with logs of wood, either oak, beech, birch, or ash, the door is closely fastened, and the joints smeared with clay; the fires are now lighted and kept up all day, till the cylinders are red-hot; at night they are allowed to cool. In the morning, the charcoal, into which the wood is now converted, is withdrawn, and a fresh charge supplied; it is then found that about thirty or forty gallons of liquid has condensed in the main tube from each cylinder, the remainder being charcoal and gases which pass off; the liquid is acid, brown, and very offensive, and contains acetic acid, tar, and several other ingredients, among which may be named creosote; it is from this source all the creosote, for the cure of toothache, is obtained. To purify this liquid it is first distilled, and this separates much of the tar; it is then mixed with lime, evaporated to dryness, and heated to expel the remaining tar and other impurities; it is next mixed with sulphate of soda and water, and the whole stirred together; the soda, now in union with the acetic acid, is washed out from the lime and strained quite clear; it is afterwards evaporated till it crystallises, and vitriol (sulphuric acid) then added; finally the acetic acid is distilled over, and the sulphuric acid left in union with the soda, forming sulphate of soda, to be used in a similar process for the next batch of acid. The acetic acid is now quite colourless, transparent, and very sour, possessing a fragrant smell. This is not pure acetic acid, but contains a considerable quantity of water. The acetic acid of commerce, mixed with seven times its bulk of water, forms an acid of about the strength of malt vinegar, perfectly wholesome, and agreeable as a condiment.

Pure acetic acid may be made by mixing dry acetate of potash with oil of vitriol in a retort, and distilling the acetic acid into a very cold receiver; this, when flavoured with various volatile oils, forms the aromatic vinegar sold by druggists. It is a very strong acid, and if applied to the skin will quickly blister it.

Acetate of lead, or sugar of lead, is obtained by dissolving oxide of lead in vinegar. A solution of this salt makes the goulard water so familiar to all. Acetate of lead is highly poisonous.

Acetate of copper is verdigris, and poisonous. Other acetates are used in medicine.

We may pass quickly over some other acids. They are as follows:—

Tartaric Acid (C₄H₆O₆) is contained in grape juice, and crystallizes in tabular form. The purified powdered salt is cream of Tartar.

Citric Acid (C₆H₈O₇) is found native in citrons and lemons, as well as in currants and other fruits. It is an excellent anti-scorbutic.

Malic Acid (C₄H₆O₅) is found chiefly in apples, as its name denotes (malum, an apple). It is prepared from mountain-ash berries.

Oxalic Acid (C₂H₂O₄). If we heat sugar with nitric acid we shall procure this acid. It is found in sorrel plants.

Tannic Acid (C₂₇H₂₂O₁₇). It is assumed that all vegetables with an astringent taste contain this acid. Tannin is known for its astringent qualities. The name given to this acid is derived from the fact that it possesses a property of forming an insoluble compound with water, known as leather. Tanning is the term employed. Tannin is found in many vegetable substances, but oak bark is usually employed, being the cheapest. The “pelts,” hides, or skins, have first to be freed from all fat or hair by scraping, and afterwards soaking them in lime and water. Then they are placed in the tan-pit between layers of the bark, water is pumped in, and the hides remain for weeks, occasionally being moved from pit to pit, or relaid, so as to give all an equal proportion of pressure, etc. The longer the leather is tanned—it may be a year—the better it wears.

Skins for gloves and binding are tanned with “sumach,” or alum and salt. Sometimes the leather is split by machinery for fine working. Parchment is prepared from the skins of asses, sheep, goats, and calves, which are cleaned, and rubbed smooth with pumice stone.

Tannic acid, with oxide of iron, produces Ink, for the gall-nut contains a quantity of the acid. All the black inks in use generally are composed of green vitriol (sulphate of iron) in union with some astringent vegetable matter; the best is the gall-nut, although, for cheapness, logwood and oak bark have each been used. An excellent black ink may be made by putting into a gallon stone bottle twelve ounces of bruised galls, six ounces of green vitriol, and six of common gum, and filling up the bottle with rain water; this should be kept three or four weeks before using, shaking the bottle from time to time.

Blue ink has lately been much used; it is made by dissolving newly-formed Prussian blue in a solution of oxalic acid. To make it, dissolve some yellow prussiate of potash in water in one vessel, and some sulphate of iron in another, adding a few drops of nitric acid to the sulphate of iron; now mix the two liquids, and a magnificent blue colour will appear, in the form of a light sediment; this is to be put upon a paper filter, and well washed by pouring over it warm water, and allowing it to run through; a warm solution of oxalic acid should now be mixed with it, and the Prussian blue will dissolve into a bright blue ink.

Red ink is made by boiling chips or raspings of Brazil wood in vinegar, and adding a little alum and gum; it keeps well, and is of a good colour. A red ink of more beautiful appearance, but not so durable, may be made by dissolving a few grains of carmine in two or three teaspoonfuls of spirit of hartshorn.

Marking ink is made by dissolving nitrate of silver in water, and then adding some solution of ammonia, a little gum water, and some Indian ink to colour it. Printers’ ink is made by grinding drying oil with lamp-black.

The powdered gall-nut is an excellent test for iron in water. It will turn violet if any iron be present.

Formic Acid (CH₂O₂) is the caustic means of defence employed by ants, hence the term formic. It can be artificially prepared by distilling a mixture of sugar, binoxide of manganese, and sulphuric acid. On the skin it will raise blisters.

Lactic Acid (C₃H₆O₃) is present in vegetable and animal substances. Sour whey contains it, and the presence of the acid in the whey accounts for its power of removing from table-linen stains. When what is called “lactic fermentation” occurs, milk is said to be “turned.”

II.

Bases.

The definition of a base is not easy. We have described bases as substances which, combining with acids, form salts, but the definition of a base is as unsatisfactory as that of acid or salt. All vegetable bases contain nitrogen, are usually very bitter, possess no smell or colour, and are insoluble in water. They are usually strong poisons, but very useful in medicine.

The most important are the following bases:—

Quinine is contained in the cinchona (yellow) bark. One hundred parts of the bark have been calculated to yield three of quinine.

Morphine is the poisonous base of opium, which is the juice of the poppy, and is prepared chiefly in India and China.

Nicotine is the active principle of tobacco, and varies in quantity in different tobaccos. Havannah tobacco possesses the least. It is a powerful poison, very oily, volatile, and inflammable.

Conia is prepared from the hemlock. It is fluid and volatile. It is also a deadly poison, and paralyses the spine directly.

Strychnine is found in poisonous trees, particularly in the nux-vomica seeds of Coromandel. It produces lock-jaw and paralysis. There is no antidote for strychnine; emetics are the only remedy.

The above are chiefly remarkable for their uses in medicine, and in consequence of their highly poisonous character are best left alone by unpractised hands.

A German chemist, named Serturner, was the first to extract the active principle from Opium. The question of opium importation has lately been attracting much attention, and the opinions concerning its use are divided. Probably in moderation, and when used by ordinary people (not demoralized creatures), it does little harm.

Opium is the juice of the “common” poppy, and derives its name from the Greek opos, juice. The plant is cultivated in India, Persia, and Turkey. After the poppy has flowered the natives go round, and with a sharp instrument wound, or puncture, every poppy head. This is done very early in the morning, and under the influence of the sun during the day the juice oozes out. Next morning the drops are scraped off. The juice is then placed in pots, dried, and sent for export. The “construction” of opium is very complicated, for it contains a number of ingredients, the most important being morphia, narcotine, meconic acid, and codeia. It is to the first named constituent that the somnolent effect of opium is due.

III.

Indifferent Substances.

There are a great number of so-called “indifferent” substances to which we cannot be indifferent. Such bodies as these have neither acid nor basic properties, and stand no comparison with salts. They are of great importance, forming, as they do, the principal nutriment of animals. Some contain nitrogen, some do not; they may therefore be divided into nitrogenous and non-nitrogenous substances; the former for solid portions of the body, the latter for warmth.

We will take the latter first, and speak of some of them—such as starch, gum, sugar, etc.

Starch is found in the roots of grain, in the potato, dahlia, artichoke, etc., and by crushing the parts of the plant, and washing them, the starch can be collected as a sediment. In cold water and in spirits of wine starch is insoluble. The various kinds of starch usually take their names from the plants whence they come. Arrowroot is obtained from the West Indian plant Maranta Arundinacea. Cassava and tapioca are from the manioc; sago, from the sago palm; wheat starch, and potato starch are other examples.

If starch be baked in an oven at a temperature of about 300° it becomes, to a great extent, soluble in cold water, forming what is called “British gum”; this is largely used for calico printing and other purposes; if boiled in water under great pressure, so that the temperature can be raised to the same degree, it is also changed into an adhesive sort of gum, “mucilage”; this is the substance made use of by the government officials to spread over the backs of postage and receipt stamps to make them adhere. The starch of grain, during germination, or growth, contains diastase, which converts the starch into gum and sugar; the same effect can be produced by heating starch with diluted sulphuric acid.

Gum found in plants is chiefly procured from the Mimosa trees, from which it flows in drops, and is called Gum Arabic. There are other so-called “gums,” but this is the one generally referred to.

Sugar exists in fruits, roots, and in the stalks of plants, in the juice of the cane, maple, and beet-root particularly. The canes are crushed, the juice is clarified with lime to prevent fermentation, and the liquid is evaporated. It is then granulated and cleared from the molasses. Sugar, when heated, becomes dark, and is called “caramel.” It is used for colouring brandy, and gives much difficulty to the sugar refiners.

Sugar refining is conducted as follows. The raw (brown) sugar is mixed into a paste with water, and allowed to drain. The sugar thus becomes white. It is then dissolved in water, with animal charcoal and bullocks’ blood. The liquid is boiled, and put into a dark cistern with holes at the bottom, and cotton fibres being fastened in the holes, are hung into another dark cistern, into which the liquid runs pure and white. It is then pumped into a copper vessel,—vacuum pan,—and condensed to the proper consistence. Subsequently it is poured into conical moulds, and pure syrup poured upon the crystal shapes. The caramel is then removed through a hole at the end. The moulds or loaves are then dried, and if not even or elegant they are turned in a lathe. Finally they are packed up as “loaf sugar.” Sugar undergoes no decomposition, and is the cause of non-decomposition in other substances. For this reason it is employed in “preserving” fruit, etc. Sugar is obtained from beet by crushing and rasping the roots, as the cane is treated.

Spirit of Wine, or Alcohol, is not a natural product. It is found by the decomposition of grape-sugar by fermentation. There is a series of alcohols which exhibit a regular gradation, founded, so to speak, upon one, two, or three molecules of water. They are called respectively alcohols, glycols, and glycerins. Thus we have—

• Alcohols.
• Methylic alcohol.
• Ethylic “
• Prophylic “
• Amylic “
• Glycols.
• Enthelein glycol.
• Prophylene “
• Butylene “
• Amylene “
• Glycerins.
• (Ordinary Glycerine is the only one known.)

The cetyl and melissylic alcohols are contained in spermaceti and bees-wax respectively. The usual alcohol is the Vinic, a transparent, colourless liquid, which is the spirituous principle of wine, spirits, and beer, and when sugar is fermented the alcohol and carbonic acid remain.

Spirits of wine has a very powerful affinity for water, and thus the use of stimulants in great quantity is to be deprecated, for alcohol absorbs the water from the mucous membranes of the stomach and the mouth, making them dry and hard. The state of “intoxication,” unfortunately so familiar, is the effect produced by alcohol upon the nerves. We append a list of the beverages which are most in use, and the percentage of alcohol in each according to Professor Hart:—

Spirit of wine is contained in many mixtures, and for the purpose of ascertaining how much alcohol may be in wine, or any other liquid, a hydrometer is used (fig. 432). This instrument consists of a glass tube with a bulb at the end. It is put into water, and the place the water “cuts” is marked by a line on the stem, and called zero 0°. Spirit of wine has less specific gravity than water, so in absolute alcohol the instrument will sink lower than in water, and will descend to a point which is marked 100. In any mixture of alcohol and water, of course the hydrometer will rise or sink between the extreme points accordingly as the mixture may contain less alcohol or more. So a scale can be furnished. The instrument, as described, was invented by MM. Gay-Lussac and Tralles, and called the “percentage” hydrometer. There are many other instruments marked in a more or less arbitrary manner. We append a comparative table of a few hydrometers. (See page 420.)

Ether, or sulphuric ether, is a mixture of spirits of wine with sulphuric acid, and distilled. It loses water, and the product is ether, which is volatile, and transparent, with a peculiarly penetrating odour. It will not mix with water, and if inhaled will produce a similar effect to chloroform.

Comparative Table of Hydrometers.

Chloroform is transparent, and will sink in water. Diluted alcohol with hypo-chloride of lime, will produce it. When inhaled, chloroform produces a pleasing insensibility to pain, and is useful in surgery.

A certain compound of alcohol with mercury dissolved in nitric acid will cause decomposition, and white crystals will eventuate. These compound crystals are termed fulminating mercury.

We must now pass rapidly over the few remaining subjects we have to notice, such as fats and soaps, wax, oils, etc.

Fats are of the greatest use to man, particularly in cold climates, for upon them depends the heat of the body. Fatty acid, if liquid, is known as oleic acid; if solid, stearic acid. Soaps are compounds of fatty acids. Many “fats” are consumed as food, others as fuel or for lighting purposes, in the shape of oils. Such oils are not primarily useful for burning. Petroleum and other mineral oils are found in enormous quantities in America.

There are what we term fixed oils, and essential or volatile oils. A list is annexed as given by “Hadyn’s Dictionary of Science”:—

Fixed Oils.

• Drying.
• Linseed oil.
• Poppy oil.
• Sunflower oil.
• Walnut oil.
• Tobacco-seed oil.
• Cress-seed oil.
• Non-Drying.
• Almond oil.
• Castor oil.
• Colza oil.
• Oil of mustard.
• Rape-seed oil.
• Olive oil, etc.

Essential Oils.

• Oil of anise.
• Oil of bergamot.
• Oil of carraway.
• Oil of cassia.
• Oil of cedar.
• Oil of cloves.
• Oil of lavender.
• Oil of lemon.
• Oil of mint.
• Oil of myrrh.
• Oil of nutmeg.
• Oil of peppermint.
• Oil of rose.
• Oil of turpentine.

Vegetable oils are obtained by crushing seeds; animal oils come from the whale and seal tribe. Paraffin oil comes from coal. Linseed is a very drying oil, and on it depends the drying power of paint. We know olive oil will not dry on exposure to the air. Oiled silk is made with linseed oil. When oil is drying in the air considerable heat is evolved, and if oiled substances be left near others likely to catch fire, spontaneous combustion may ensue. Oil of turpentine is found in the pine and fir trees, and many of the oils above mentioned are used by perfumers, etc., the rose oil, or attar of roses, being an Eastern compound.

Allied to the volatile oils are the RESINS, which are non-conductors of electricity. They are vegetable products. They are soluble in alcohol, in the volatile oils, or in ether, and these solutions are called varnishes; the solvent evaporates and leaves the coating. Turpentine, copal, mastic, shellac, caoutchouc, and gutta-percha are all resinous bodies. Amber is a mineral resin, which was by the ancients supposed to be the “tears of birds” dropped upon the seashore. Moore refers to this in his poetic “Farewell to Araby’s Daughter”—

Amber is not soluble either in water or alcohol; it is, however, soluble in sulphuric acid. It takes a good polish, and when rubbed is very electrical. It is composed of water, an acid, some oil, and an inflammable gas, which goes off when the amber is distilled.

The well-known camphor is got from a tree called the “Laurus Camphora”; it is a white, waxy substance, and can be obtained by oxidizing certain volatile oils. It is generally produced from the Laurus Camphora in a “still.” The behaviour of a piece of camphor in pure water is curious, but its motions can be at once arrested by touching the water or dropping oil on the surface. This phenomenon is due to the surface tension of the liquid, which diminishes when it is in contact with the vapour of the substance.

Nitrogenous Substances.

There are certain albuminous compounds which we must mention here. These are albumen, fibrine, and caseine. Albumen is the white of egg; fibrine is, when solid, our flesh and muscular fibre, while caseine is the substance of cheese. These are very important compounds, and the albuminous bodies are of the very highest importance as food, for the solid portion of blood, brain, and flesh consist, in a great measure, of them. Albumen, fibrine, and caseine contain carbon, hydrogen, nitrogen, and oxygen, with sulphur and phosphorus.

Albumen. The most familiar and the almost pure form of albumen is in the white of eggs, which is albuminate of sodium. It also exists in the serum of the blood, and therefore it is largely found in the animal kingdom. It can also be extracted from seed or other vegetable substances, but it is essentially the same. Albumen is very useful as an antidote to metallic poisons. It forms about 7 per cent. of human blood. It is soluble up to about 140° Fah.; it then solidifies, and is precipitated in a white mass. Albumen is used in the purification of sugar, etc.

Fibrine is found in a liquid condition in blood. The vegetable fibrine (gluten) is prepared by kneading wheat flour in a bag till the washings are no longer whitened. Like albumen it is found both in a solid and liquid state.

Caseine is seen in the skin which forms upon milk when heated, and forms about 3 per cent. of milk, where it exists in a soluble state, owing to the presence of alkali; but caseine, like albumen, is only soluble in alkaline solutions. As we have said, it is the principal constituent of cheeses. Caseine is precipitated by the lactic acid of milk, which is produced by keeping the milk too warm. Caseine, or curds, as they are called, are thus precipitated. The milk is said to be “sour,” or turned.

Milk, the food of the young of all mammalia, is composed chiefly of water, a peculiar kind of sugar, butter, and caseine. It is this sugar in milk which causes the lactic acid mentioned above. The actual constituents of milk are as follows:—

The sugar of milk is non-fermenting, and can be procured from whey by evaporation.

Decomposition.

We have seen that animals and plants are composed of many different substances, and so it will be at once understood that these substances can be separated from each other, and then the decomposition of the body will be completed. When the sap sinks or dries up in plants they are dead. When our heart ceases to beat and our blood to flow we die, and then, gradually but surely, decay sets in. There is no fuel left to keep the body warm; cold results, and the action of oxygen of the air and light or water decays the body, according to the great and unalterable laws of Nature. “Dust thou art, and unto dust shalt thou return,” is an awful truth. The constituents of our bodies must be resolved again, and the unfailing law of chemical attraction is carried out, whereby the beautiful organism, deprived of the animating principle, seeks to render itself into less complicated groups and their primary elements.

This resolution of the organic bodies is decomposition, or “spontaneous decomposition,” and is called decay, fermentation, or putrefaction, according to circumstances. The Egyptians, by first drying the bodies of the dead (and then embalming them), removed one great source of decay—viz., water, and afterwards, by the addition of spices, managed to arrest putrefaction.

Fermentation is familiar in its results, which may be distilled for spirituous liquors, or merely remain fermented, as beer and wine. Fusel oil is prepared from potatoes, rum from cane sugar, arrack from rice. The power of fermentation exists in nature everywhere, and putrefaction is considered to be owing to the presence of minute germs in the atmosphere, upon which Professors Tyndall and Huxley have discoursed eloquently.

Plants are subjected to a process of decomposition, which has been termed “slow carbonization,” under certain circumstances which exclude the air. The gases are given off, and the carbon remains and increases. Thus we have a kind of moss becoming peat, brown coal, and coal. The immense period during which some beds of coal must have lain in the ground can only be approximately ascertained, but the remains found in the coal-measures have guided geologists in their calculations.

Having already mentioned some products of distillation, we may now close this portion of the subject and pass on to a brief consideration of minerals and crystals. We have left many things unnoticed, which in the limited space at our disposal we could not conveniently include in our sketch of chemistry and chemical phenomena.