What have been from the dawn of history to the rise of synthetic chemistry the most costly products of nature? What could tempt a merchant to brave the perils of a caravan journey over the deserts of Asia beset with Arab robbers? What induced the Portuguese and Spanish mariners to risk their frail barks on perilous waters of the Cape of Good Hope or the Horn? The chief prizes were perfumes, spices, drugs and gems. And why these rather than what now const.i.tutes the bulk of oversea and overland commerce? Because they were precious, portable and imperishable. If the merchant got back safe after a year or two with a little flask of otto of roses, a package of camphor and a few pearls concealed in his garments his fortune was made. If a single ship of the argosy sent out from Lisbon came back with a load of sandalwood, indigo or nutmeg it was regarded as a successful venture. You know from reading the Bible, or if not that, from your reading of Arabian Nights, that a few grains of frankincense or a few drops of perfumed oil were regarded as gifts worthy the acceptance of a king or a G.o.d. These products of the Orient were equally in demand by the toilet and the temple. The unctorium was an adjunct of the Roman bathroom. Kings had to be greased and fumigated before they were thought fit to sit upon a throne. There was a theory, not yet altogether extinct, that medicines brought from a distance were most efficacious, especially if, besides being expensive, they tasted bad like myrrh or smelled bad like asafetida. And if these failed to save the princely patient he was embalmed in aromatics or, as we now call them, antiseptics of the benzene series.

Today, as always, men are willing to pay high for the t.i.tillation of the senses of smell and taste. The African savage will trade off an ivory tusk for a piece of soap reeking with synthetic musk. The clubman will pay $10 for a bottle of wine which consists mostly of water with about ten per cent. of alcohol, worth a cent or two, but contains an unweighable amount of the "bouquet" that can only be produced on the sunny slopes of Champagne or in the valley of the Rhine. But very likely the reader is quite as extravagant, for when one buys the natural violet perfumery he is paying at the rate of more than $10,000 a pound for the odoriferous oil it contains; the rest is mere water and alcohol. But you would not want the pure undiluted oil if you could get it, for it is unendurable. A single whiff of it paralyzes your sense of smell for a time just as a loud noise deafens you.

Of the five senses, three are physical and two chemical. By touch we discern pressures and surface textures. By hearing we receive impressions of certain air waves and by sight of certain ether waves.

But smell and taste lead us to the heart of the molecule and enable us to tell how the atoms are put together. These twin senses stand like sentries at the portals of the body, where they closely scrutinize everything that enters. Sounds and sights may be disagreeable, but they are never fatal. A man can live in a boiler factory or in a cubist art gallery, but he cannot live in a room containing hydrogen sulfide. Since it is more important to be warned of danger than guided to delights our senses are made more sensitive to pain than pleasure. We can detect by the smell one two-millionth of a milligram of oil of roses or musk, but we can detect one two-billionth of a milligram of mercaptan, which is the vilest smelling compound that man has so far invented. If you do not know how much a milligram is consider a drop picked up by the point of a needle and imagine that divided into two billion parts. Also try to estimate the weight of the odorous particles that guide a dog to the fox or warn a deer of the presence of man. The unaided nostril can rival the spectroscope in the detection and a.n.a.lysis of unweighable amounts of matter.

What we call flavor or savor is a joint effect of taste and odor in which the latter predominates. There are only four tastes of importance, acid, alkaline, bitter and sweet. The acid, or sour taste, is the perception of hydrogen atoms charged with positive electricity. The alkaline, or soapy taste, is the perception of hydroxyl radicles charged with negative electricity. The bitter and sweet tastes and all the odors depend upon the chemical const.i.tution of the compound, but the laws of the relation have not yet been worked out. Since these sense organs, the taste and smell buds, are sunk in the moist mucous membrane they can only be touched by substances soluble in water, and to reach the sense of smell they must also be volatile so as to be diffused in the air inhaled by the nose. The "taste" of food is mostly due to the volatile odors of it that creep up the back-stairs into the olfactory chamber.

A chemist given an unknown substance would have to make an elementary a.n.a.lysis and some tedious tests to determine whether it contained methyl or ethyl groups, whether it was an aldehyde or an ester, whether the carbon atoms were singly or doubly linked and whether it was an open chain or closed. But let him get a whiff of it and he can give instantly a pretty shrewd guess as to these points. His nose knows.

Although the chemist does not yet know enough to tell for certain from looking at the structural formula what sort of odor the compound would have or whether it would have any, yet we can divide odoriferous substances into cla.s.ses according to their const.i.tution. What are commonly known as "fruity" odors belong mostly to what the chemist calls the fatty or aliphatic series. For instance, we may have in a ripe fruit an alcohol (say ethyl or common alcohol) and an acid (say acetic or vinegar) and a combination of these, the ester or organic salt (in this case ethyl acetate), which is more odorous than either of its components. These esters of the fatty acids give the characteristic savor to many of our favorite fruits, candies and beverages. The pear flavor, amyl acetate, is made from acetic acid and amyl alcohol--though amyl alcohol (fusel oil) has a detestable smell. Pineapple is ethyl butyrate--but the acid part of it (butyric acid) is what gives Limburger cheese its aroma. These essential oils are easily made in the laboratory, but cannot be extracted from the fruit for separate use.

If the carbon chain contains one or more double linkages we get the "flowery" perfumes. For instance, here is the symbol of geraniol, the chief ingredient of otto of roses:

(CH_{3})_{2}C = CHCH_{2}CH_{2}C(CH_{3})_{2} = CHCH_{2}OH

The rose would smell as sweet under another name, but it may be questioned whether it would stand being called by the name of dimethyl-2-6-octadiene-2-6-ol-8. Geraniol by oxidation goes into the aldehyde, citral, which occurs in lemons, oranges and verbena flowers.

Another compound of this group, linalool, is found in lavender, bergamot and many flowers.

Geraniol, as you would see if you drew up its structural formula in the way I described in the last chapter, contains a chain of six carbon atoms, that is, the same number as make a benzene ring. Now if we shake up geraniol and other compounds of this group (the diolefines) with diluted sulfuric acid the carbon chain hooks up to form a benzene ring, but with the other carbon atoms stretched across it; rather too complicated to depict here. These "bridged rings" of the formula C_{5}H_{8}, or some multiple of that, const.i.tute the important group of the terpenes which occur in turpentine and such wild and woodsy things as sage, lavender, caraway, pine needles and eucalyptus. Going further in this direction we are led into the realm of the heavy oriental odors, patchouli, sandalwood, cedar, cubebs, ginger and camphor. Camphor can now be made directly from turpentine so we may be independent of Formosa and Borneo.

When we have a six carbon ring without double linkings (cyclo-aliphatic) or with one or two such, we get soft and delicate perfumes like the violet (ionone and irone). But when these pa.s.s into the benzene ring with its three double linkages the odor becomes more powerful and so characteristic that the name "aromatic compound" has been extended to the entire cla.s.s of benzene derivatives, although many of them are odorless. The essential oils of jasmine, orange blossoms, musk, heliotrope, tuberose, ylang ylang, etc., consist mostly of this cla.s.s and can be made from the common source of aromatic compounds, coal tar.

The synthetic flavors and perfumes are made in the same way as the dyes by starting with some coal-tar product or other crude material and building up the molecule to the desired complexity. For instance, let us start with phenol, the ill-smelling and poisonous carbolic acid of disagreeable a.s.sociations and evil fame. Treat this to soda-water and it is transformed into salicylic acid, a white odorless powder, used as a preservative and as a rheumatism remedy. Add to this methyl alcohol which is obtained by the destructive distillation of wood and is much more poisonous than ordinary ethyl alcohol. The alcohol and the acid heated together will unite with the aid of a little sulfuric acid and we get what the chemist calls methyl salicylate and other people call oil of wintergreen, the same as is found in wintergreen berries and birch bark. We have inherited a taste for this from our pioneer ancestors and we use it extensively to flavor our soft drinks, gum, tooth paste and candy, but the Europeans have not yet found out how nice it is.

But, starting with phenol again, let us heat it with caustic alkali and chloroform. This gives us two new compounds of the same composition, but differing a little in the order of the atoms. If you refer back to the diagram of the benzene ring which I gave in the last chapter, you will see that there are six hydrogen atoms attached to it. Now any or all these hydrogen atoms may be replaced by other elements or groups and what the product is depends not only on what the new elements are, but where they are put. It is like spelling words. The three letters _t_, _r_ and _a_ mean very different things according to whether they are put together as _art_, _tar_ or _rat_. Or, to take a more apposite ill.u.s.tration, every hostess knows that the success of her dinner depends upon how she seats her guests around the table. So in the case of aromatic compounds, a little difference in the seating arrangement around the benzene ring changes the character. The two derivatives of phenol, which we are now considering, have two subst.i.tuting groups. One is--O-H (called the hydroxyl group). The other is--CHO (called the aldehyde group). If these are opposite (called the para position) we have an odorless white solid. If they are side by side (called the ortho position) we have an oil with the odor of meadowsweet. Treating the odorless solid with methyl alcohol we get audepine (or anisic aldehyde) which is the perfume of hawthorn blossoms. But treating the other of the twin products, the fragrant oil, with dry acetic acid ("Perkin's reaction") we get c.u.marin, which is the perfume part of the tonka or tonquin beans that our forefathers used to carry in their snuff boxes.

One ounce of c.u.marin is equal to four pounds of tonka beans. It smells sufficiently like vanilla to be used as a subst.i.tute for it in cheap extracts. In perfumery it is known as "new mown hay."

You may remember what I said on a former page about the career of William Henry Perkin, the boy who loved chemistry better than eating, and how he discovered the coal-tar dyes. Well, it is also to his ingenious mind that we owe the starting of the coal-tar perfume business which has had almost as important a development. Perkin made c.u.marin in 1868, but this, like the dye industry, escaped from English hands and flew over the North Sea. Before the war Germany was exporting $1,500,000 worth of synthetic perfumes a year. Part of these went to France, where they were mixed and put up in fancy bottles with French names and sold to Americans at fancy prices.

The real vanilla flavor, vanillin, was made by Tiemann in 1874. At first it sold for nearly $800 a pound, but now it may be had for $10. How extensively it is now used in chocolate, ice cream, soda water, cakes and the like we all know. It should be noted that c.u.marin and vanillin, however they may be made, are not imitations, but identical with the chief const.i.tuent of the tonka and vanilla beans and, of course, are equally wholesome or harmless. But the nice palate can distinguish a richer flavor in the natural extracts, for they contain small quant.i.ties of other savory ingredients.

A true perfume consists of a large number of odoriferous chemical compounds mixed in such proportions as to produce a single harmonious effect upon the sense of smell in a fine brand of perfume may be compounded a dozen or twenty different ingredients and these, if they are natural essences, are complex mixtures of a dozen or so distinct substances. Perfumery is one of the fine arts. The perfumer, like the orchestra leader, must know how to combine and coordinate his instruments to produce a desired sensation. A Wagnerian opera requires 103 musicians. A Strauss opera requires 112. Now if the concert manager wants to economize he will insist upon cutting down on the most expensive musicians and dropping out some of the others, say, the supernumerary violinists and the man who blows a single blast or tinkles a triangle once in the course of the evening. Only the trained ear will detect the difference and the manager can make more money.

Suppose our mercenary impresario were unable to get into the concert hall of his famous rival. He would then listen outside the window and a.n.a.lyze the sound in this fashion: "Fifty per cent. of the sound is made by the tuba, 20 per cent. by the ba.s.s drum, 15 per cent. by the 'cello and 10 per cent. by the clarinet. There are some other instruments, but they are not loud and I guess if we can leave them out n.o.body will know the difference." So he makes up his orchestra out of these four alone and many people do not know the difference.

The cheap perfumer goes about it in the same way. He a.n.a.lyzes, for instance, the otto or oil of roses which cost during the war $400 a pound--if you could get it at any price--and he finds that the chief ingredient is geraniol, costing only $5, and next is citronelol, costing $20; then comes nerol and others. So he makes up a cheap brand of perfumery out of three or four such compounds. But the genuine oil of roses, like other natural essences, contains a dozen or more const.i.tuents and to leave many of them out is like reducing an orchestra to a few loud-sounding instruments or a painting to a three-color print.

A few years ago an attempt was made to make music electrically by producing separately each kind of sound vibration contained in the instruments imitated. Theoretically that seems easy, but practically the tone was not satisfactory because the tones and overtones of a full orchestra or even of a single violin are too numerous and complex to be reproduced individually. So the synthetic perfumes have not driven out the natural perfumes, but, on the contrary, have aided and stimulated the growth of flowers for essences. The otto or attar of roses, favorite of the Persian monarchs and romances, has in recent years come chiefly from Bulgaria. But wars are not made with rosewater and the Bulgars for the last five years have been engaged in other business than cultivating their own gardens. The alembic or still was invented by the Arabian alchemists for the purpose of obtaining the essential oil or attar of roses. But distillation, even with the aid of steam, is not altogether satisfactory. For instance, the distilled rose oil contains anywhere from 10 to 74 per cent. of a paraffin wax (stearopten) that is odorless and, on the other hand, phenyl-ethyl alcohol, which is an important const.i.tuent of the scent of roses, is broken up in the process of distillation. So the perfumer can improve on the natural or rather the distilled oil by leaving out part of the paraffin and adding the missing alcohol. Even the imported article taken direct from the still is not always genuine, for the wily Bulgar sometimes "increases the yield" by sprinkling his roses in the vat with synthetic geraniol just as the wily Italian pours a barrel of American cottonseed oil over his olives in the press.

Another method of extracting the scent of flowers is by _enfleurage_, which takes advantage of the tendency of fats to absorb odors. You know how b.u.t.ter set beside fish in the ice box will get a fishy flavor. In _enfleurage_ moist air is carried up a tower pa.s.sing alternately over trays of fresh flowers, say violets, and over gla.s.s plates covered with a thin layer of lard. The perfumed lard may then be used as a pomade or the perfume may be extracted by alcohol.

But many sweet flowers do not readily yield an essential oil, so in such oases we have to rely altogether upon more or less successful subst.i.tutes. For instance, the perfumes sold under the names of "heliotrope," "lily of the valley," "lilac," "cyclamen," "honeysuckle,"

"sweet pea," "arbutus," "mayflower" and "magnolia" are not produced from these flowers but are simply imitations made from other essences, synthetic or natural. Among the "thousand flowers" that contribute to the "Eau de Mille Fleurs" are the civet cat, the musk deer and the sperm whale. Some of the published formulas for "Jockey Club" call for civet or ambergris and those of "Lavender Water" for musk and civet. The less said about the origin of these three animal perfumes the better.

Fortunately they are becoming too expensive to use and are being displaced by synthetic products more agreeable to a refined imagination.

The musk deer may now be saved from extinction since we can make tri-nitro-butyl-xylene from coal tar. This synthetic musk pa.s.ses muster to human nostrils, but a cat will turn up her nose at it. The synthetic musk is not only much cheaper than the natural, but a dozen times as strong, or let us say, goes a dozen times as far, for n.o.body wants it any stronger.

Such powerful scents as these are only pleasant when highly diluted, yet they are, as we have seen, essential ingredients of the finest perfumes.

For instance, the natural oil of jasmine and other flowers contain traces of indols and skatols which have most disgusting odors. Though our olfactory organs cannot detect their presence yet we perceive their absence so they have to be put into the artificial perfume. Just so a brief but violent discord in a piece of music or a glaring color contrast in a painting may be necessary to the harmony of the whole.

It is absurd to object to "artificial" perfumes, for practically all perfumes now sold are artificial in the sense of being compounded by the art of the perfumer and whether the materials he uses are derived from the flowers of yesteryear or of Carboniferous Era is n.o.body's business but his. And he does not tell. The materials can be purchased in the open market. Various recipes can be found in the books. But every famous perfumer guards well the secret of his formulas and hands it as a legacy to his posterity. The ancient Roman family of Frangipani has been made immortal by one such hereditary recipe. The Farina family still claims to have the exclusive knowledge of how to make Eau de Cologne. This famous perfume was first compounded by an Italian, Giovanni Maria Farina, who came to Cologne in 1709. It soon became fashionable and was for a time the only scent allowed at some of the German courts. The various published recipes contain from six to a dozen ingredients, chiefly the oils of neroli, rosemary, bergamot, lemon and lavender dissolved in very pure alcohol and allowed to age like wine. The invention, in 1895, of artificial neroli (orange flowers) has improved the product.

French perfumery, like the German, had its origin in Italy, when Catherine de' Medici came to Paris as the bride of Henri II. She brought with her, among other artists, her perfumer, Sieur Toubarelli, who established himself in the flowery land of Gra.s.se. Here for four hundred years the industry has remained rooted and the family formulas have been handed down from generation to generation. In the city of Gra.s.se there were at the outbreak of the war fifty establishments making perfumes. The French perfumer does not confine himself to a single sense. He appeals as well to sight and sound and a.s.sociation. He adds to the attractiveness of his creation by a quaintly shaped bottle, an artistic box and an enticing name such as "Dans les Nues," "Le Coeur de Jeannette," "Nuit de Chine," "Un Air Embaume," "Le Vertige," "Bon Vieux Temps," "L'Heure Bleue," "Nuit d'Amour," "Quelques Fleurs," "Djer-Kiss."

The requirements of a successful scent are very strict. A perfume must be lasting, but not strong. All its ingredients must continue to evaporate in the same proportion, otherwise it will change odor and deteriorate. Scents kill one another as colors do. The minutest trace of some impurity or foreign odor may spoil the whole effect. To mix the ingredients in a vessel of any metal but aluminum or even to filter through a tin funnel is likely to impair the perfume. The odoriferous compounds are very sensitive and unstable bodies, otherwise they would have no effect upon the olfactory organ. The combination that would be suitable for a toilet water would not be good for a talc.u.m powder and might spoil in a soap. Perfumery is used even in the "scentless" powders and soaps. In fact it is now used more extensively, if less intensively, than ever before in the history of the world. During the Unwashed Ages, commonly called the Dark Ages, between the destruction of the Roman baths and the construction of the modern bathroom, the art of the perfumer, like all the fine arts, suffered an eclipse. "The odor of sanct.i.ty" was in highest esteem and what that odor was may be imagined from reading the lives of the saints. But in the course of centuries the refinements of life began to seep back into Europe from the East by means of the Arabs and Crusaders, and chemistry, then chiefly the art of cosmetics, began to revive. When science, the greatest democratizing agent on earth, got into action it elevated the poor to the ranks of kings and priests in the delights of the palate and the nose. We should not despise these delights, for the pleasure they confer is greater, in amount at least, than that of the so-called higher senses. We eat three times a day; some of us drink oftener; few of us visit the concert hall or the art gallery as often as we do the dining room. Then, too, these primitive senses have a stronger influence upon our emotional nature than those acquired later in the course of evolution. As Kipling puts it:

Smells are surer than sounds or sights To make your heart-strings crack.

VI

CELLULOSE

Organic compounds, on which our life and living depend, consist chiefly of four elements: carbon, hydrogen, oxygen and nitrogen. These compounds are sometimes hard to a.n.a.lyze, but when once the chemist has ascertained their const.i.tution he can usually make them out of their elements--if he wants to. He will not want to do it as a business unless it pays and it will not pay unless the manufacturing process is cheaper than the natural process. This depends primarily upon the cost of the crude materials. What, then, is the market price of these four elements?

Oxygen and nitrogen are free as air, and as we have seen in the second chapter, their direct combination by the electric spark is possible.

Hydrogen is free in the form of water but expensive to extricate by means of the electric current. But we need more carbon than anything else and where shall we get that? Bits of crystallized carbon can be picked up in South Africa and elsewhere, but those who can afford to buy them prefer to wear them rather than use them in making synthetic food.

Graphite is rare and hard to melt. We must then have recourse to the compounds of carbon. The simplest of these, carbon dioxide, exists in the air but only four parts in ten thousand by volume. To extract the carbon and get it into combination with the other elements would be a difficult and expensive process. Here, then, we must call in cheap labor, the cheapest of all laborers, the plants. Pine trees on the highlands and cotton plants on the lowlands keep their green traps set all the day long and with the captured carbon dioxide build up cellulose. If, then, man wants free carbon he can best get it by charring wood in a kiln or digging up that which has been charred in nature's kiln during the Carboniferous Era. But there is no reason why he should want to go back to elemental carbon when he can have it already combined with hydrogen in the remains of modern or fossil vegetation. The synthetic products on which modern chemistry prides itself, such as vanillin, camphor and rubber, are not built up out of their elements, C, H and O, although they might be as a laboratory stunt. Instead of that the raw material of the organic chemist is chiefly cellulose, or the products of its recent or remote destructive distillation, tar and oil.

It is unnecessary to tell the reader what cellulose is since he now holds a specimen of it in his hand, pretty pure cellulose except for the sizing and the specks of carbon that mar the whiteness of its surface.

This utilization of cellulose is the chief cause of the difference between the modern world and the ancient, for what is called the invention of printing is essentially the inventing of paper. The Romans made type to stamp their coins and lead pipes with and if they had had paper to print upon the world might have escaped the Dark Ages. But the clay tablets of the Babylonians were c.u.mbersome; the wax tablets of the Greeks were perishable; the papyrus of the Egyptians was fragile; parchment was expensive and penning was slow, so it was not until literature was put on a paper basis that democratic education became possible. At the present time sheepskin is only used for diplomas, treaties and other antiquated doc.u.ments. And even if your diploma is written in Latin it is likely to be made of sulfated cellulose.

The textile industry has followed the same law of development that I have indicated in the other industries. Here again we find the three stages of progress, (1) utilization of natural products, (2) cultivation of natural products, (3) manufacture of artificial products. The ancients were dependent upon plants, animals and insects for their fibers. China used silk, Greece and Rome used wool, Egypt used flax and India used cotton. In the course of cultivation for three thousand years the animal and vegetable fibers were lengthened and strengthened and cheapened. But at last man has risen to the level of the worm and can spin threads to suit himself. He can now rival the wasp in the making of paper. He is no longer dependent upon the flax and the cotton plant, but grinds up trees to get his cellulose. A New York newspaper uses up nearly 2000 acres of forest a year. The United States grinds up about five million cords of wood a year in the manufacture of pulp for paper and other purposes.

In making "mechanical pulp" the blocks of wood, mostly spruce and hemlock, are simply pressed sidewise of the grain against wet grindstones. But in wood fiber the cellulose is in part combined with lignin, which is worse than useless. To break up the ligno-cellulose combine chemicals are used. The logs for this are not ground fine, but cut up by disk chippers. The chips are digested for several hours under heat and pressure with acid or alkali. There are three processes in vogue. In the most common process the reagent is calcium sulfite, made by pa.s.sing sulfur fumes (SO_{2}) into lime water. In another process a solution of caustic of soda is used to disintegrate the wood. The third, known as the "sulfate" process, should rather be called the sulfide process since the active agent is an alkaline solution of sodium sulfide made by roasting sodium sulfate with the carbonaceous matter extracted from the wood. This sulfate process, though the most recent of the three, is being increasingly employed in this country, for by means of it the resinous pine wood of the South can be worked up and the final product, known as kraft paper because it is strong, is used for wrapping.

But whatever the process we get nearly pure cellulose which, as you can see by examining this page under a microscope, consists of a tangled web of thin white fibers, the remains of the original cell walls. Owing to the severe treatment it has undergone wood pulp paper does not last so long as the linen rag paper used by our ancestors. The pages of the newspapers, magazines and books printed nowadays are likely to become brown and brittle in a few years, no great loss for the most part since they have served their purpose, though it is a pity that a few copies of the worst of them could not be printed on permanent paper for preservation in libraries so that future generations could congratulate themselves on their progress in civilization.

But in our absorption in the printed page we must not forget the other uses of paper. The paper clothing, so often prophesied, has not yet arrived. Even paper collars have gone out of fashion--if they ever were in. In Germany during the war paper was used for socks, shirts and shoes as well as handkerchiefs and napkins but it could not stand wear and washing. Our sanitary engineers have set us to drinking out of sharp-edged paper cups and we blot our faces instead of wiping them.

Twine is spun of paper and furniture made of the twine, a rival of rattan. Cloth and matting woven of paper yarn are being used for burlap and gra.s.s in the making of bags and suitcases.

Here, however, we are not so much interested in manufactures of cellulose itself, that is, wood, paper and cotton, as we are in its chemical derivatives. Cellulose, as we can see from the symbol, C_{6}H_{10}O_{5}, is composed of the three elements of carbon, hydrogen and oxygen. These are present in the same proportion as in starch (C_{6}H_{10}O_{5}), while glucose or grape sugar (C_{6}H_{12}O_{6}) has one molecule of water more. But glucose is soluble in cold water and starch is soluble in hot, while cellulose is soluble in neither.

Consequently cellulose cannot serve us for food, although some of the vegetarian animals, notably the goat, have a digestive apparatus that can handle it. In Finland and Germany birch wood pulp and straw were used not only as an ingredient of cattle food but also put into war bread. It is not likely, however, that the human stomach even under the pressure of famine is able to get much nutriment out of sawdust. But by digesting with dilute acid sawdust can be transformed into sugars and these by fermentation into alcohol, so it would be possible for a man after he has read his morning paper to get drunk on it.

If the cellulose, instead of being digested a long time in dilute acid, is dipped into a solution of sulfuric acid (50 to 80 per cent.) and then washed and dried it acquires a hard, tough and translucent coating that makes it water-proof and grease-proof. This is the "parchment paper"

that has largely replaced sheepskin. Strong alkali has a similar effect to strong acid. In 1844 John Mercer, a Lancashire calico printer, discovered that by pa.s.sing cotton cloth or yarn through a cold 30 per cent. solution of caustic soda the fiber is shortened and strengthened.

For over forty years little attention was paid to this discovery, but when it was found that if the material was stretched so that it could not shrink on drying the twisted ribbons of the cotton fiber were changed into smooth-walled cylinders like silk, the process came into general use and nowadays much that pa.s.ses for silk is "mercerized"

cotton.

Another step was taken when Cross of London discovered that when the mercerized cotton was treated with carbon disulfide it was dissolved to a yellow liquid. This liquid contains the cellulose in solution as a cellulose xanthate and on acidifying or heating the cellulose is recovered in a hydrated form. If this yellow solution of cellulose is squirted out of tubes through extremely minute holes into acidulated water, each tiny stream becomes instantly solidified into a silky thread which may be spun and woven like that ejected from the spinneret of the silkworm. The origin of natural silk, if we think about it, rather detracts from the pleasure of wearing it, and if "he who needlessly sets foot upon a worm" is to be avoided as a friend we must hope that the advance of the artificial silk industry will be rapid enough to relieve us of the necessity of boiling thousands of baby worms in their cradles whenever we want silk stockings.

On a plain rush hurdle a silkworm lay When a proud young princess came that way.

The haughty daughter of a lordly king Threw a sidelong glance at the humble thing, Little thinking she walked in pride In the winding sheet where the silkworm died.

But so far we have not reached a stage where we can altogether dispense with the services of the silkworm. The viscose threads made by the process look as well as silk, but they are not so strong, especially when wet.

Besides the viscose method there are several other methods of getting cellulose into solution so that artificial fibers may be made from it. A strong solution of zinc chloride will serve and this process used to be employed for making the threads to be charred into carbon filaments for incandescent bulbs. Cellulose is also soluble in an ammoniacal solution of copper hydroxide. The liquid thus formed is squirted through a fine nozzle into a precipitating solution of caustic soda and glucose, which brings back the cellulose to its original form.