The chemistry of common life

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Introduction

The common life of man is full of wonders, Chemical and Physiological. Most of us pass through this life without seeing or being sensible of them, though every day our existence and our comforts ought to recall them to our minds. One main cause of this is, that our schools tell us nothing about them — do not teach those parts of modern learning which would fit us for seeing them. What most concerns the things that daily occupy our attention and cares, are in early life almost sedulously kept from our knowledge. Those who would learn anything regarding them, must subsequently teach themselves through the help of the press : hence the necessity for a Popular Chemical Literature.

It is with a view to meet this want of the Public, and at the same time to supply a Manual for the Schools, that the present Work has been projected. It treats, in what appears to be their natural order, of the air we breathe and THE water we deink, in their relations to human life and health — the soil we cultivate and the plant we rear, as the sources from which the chief

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INTRODU CTION.

sustenance of all life is obtained — the bread we eat and the beep WE cook, as the representatives of the two grand divisions of human food — the beverages we infuse, from which so much of the comfort of modern life, both savage and civilised, is derived — the sweets we extract, the history of which presents so striking an illustration of the economical value of chemical science — the liquors we ferment, so different from the sweets in their action on the system, and yet so closely connected with them in chemical history — THE NARCOTICS WE IN- DULGE in, as presenting us with an aspect of the human constitution which, both chemically and physiologically, is more mysterious and wonderful than any other we are yet acquainted with — the odours we enjoy and the smells WE dislike ; the former because of the beautiful illustration they present of the recent progress of organic chemistry in its relations to the comforts of common life, and the latter because of their intimate connection with our most important sanitary arrangements — what we breathe for and why we digest, as relating to functions of the body at once the most important to life, and the most purely chemical in their nature — the body WE cherish, as presenting many striking phenomena, and performing many interesting chemical functions not touched upon in the discussion of the preceding topics — and lastly, the circulation of matter, as exhibiting in one view the end, purpose, and method of all the changes in the natural body, in organic nature, and in the mineral kingdom, which are connected with and determine the existence of life.

INTRODUCTION.

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It has been the object of the Author in this Work, to exhibit the present condition of chemical knowledge, and of matured scientific opinion upon the subjects to which it is devoted. The reader will not be surprised, therefore, should he find in it some things which differ from what is to be found in other popular works already in his hands or on the shelves of his library.

CONTENTS OF THE FIRST VOLUME.

Chapter I. The Air We Breathe

Height of the earth’s atmosphere ; it is one of the elements of the ancients — Composition of the atmosphere. — Oxygen, preparation and properties of. — Nitrogen, preparation and properties of. — Proportions of these elements in the air ; their adaptation in kind and quantity to the existing condition of things. — Uses of the oxygen and nitrogen. — Uses of the carbonic acid ; its

importance to vegetable life. — Deleterious influence upon animal life. — The

“ Poison Valley” of Java. — Importance of the watery vapour of the air; its constant circulation. — Formation of rain and dew ; their many uses. — Accidental constituents of the air; ozone, nitric acid, and ammonia, — Vapours which rise from the surface of the earth, and saline matters from the sea,

Chapter II. The Water We Drink

Importance of water in nature. — Composition of water. — Hydrogen gas; how prepared ; the lightest of known substances, and an inflammable gas ; exists in nearly all combustible substances ; is always converted into water when these substances are burned. — In water hydrogen is combined with oxygen. — What is meant by a chemical combination. — Water without taste and smell; importance of this.— Cooling property of water.-jjRelation of water to other liquids. — It dissolves many solid substances; hence natural waters never pure. — Quantity of mineral matter in some knowu river, spring, and sea waters. — Composition of the solid matter in sea water ; in the Thames water at Kew ; and in that of the Kent Water Company. — Lime held in solution in water by carbonic acid. — Why calcareous waters encrust their channels, petrify, and deposit sediments in boilers. — Impurity of spring waters in large

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towns, about farmhouses, and near graveyards. — Composition of well water from Highgate Hill. — AVell waters in tlie dunes of Bordeaux ; their analogy to the waters of Marah. — Water absorbs its own bulk of carbonic acid at all pressures — IIow this explains the liveliness of champagne and soda-water, the bursting of bottles, the briskness and deadness of beer, fzc. — Excess of oxygen in the air contained in water ; importance of this to the lives of fishes.

Chapter III. The Soil We Cultivate

General origin of soils; natural differences in their quality; how it arises. — Stratified and unstratified rocks. — Soils of the stratified rocks. — Improved soils where different rocks intermix. — Soils of the granites, traps, and lavas.

— Agency of rains, winds, and vegetable accumulations in producing diversities of soil. — General chemical composition of soils. — Illustrations afforded by the Atlantic border of the United States. — Some plains affect sandy soils, others clay soils, and yet do not always flourish upon them. — Cause of this. — Minute chemical composition of the soil ; its mineral and organic parts. — Chemical difference between granite and trap soils. — Dependence of fertility on chemical composition. — Influence of rain and moisture, and of the degree of warmth, on comparative fertility. — District floras and crops. — Influence of man in modifying geological, chemical, and climatic tendencies. — Progress of exhausting culture in new regions ; example of North America. — Reclaiming influences of human exertion ; example of Great Britain, ... 48

Chapter IV. The Plant We Rear

A perfect plant, what. — Effects of heat upon it. — Contains carbon, water, and mineral matter. — Relations of the plant to the atr. — Structure of the leaf —

Its pores absorb carbonic acid, and give off oxygen gas — Relations to water.

— Structure of the root — Purposes served by water — Relations to the soil. — ^ Plants affect peaty, sandy, loamy, or clay soils.— Effects of the drain, of lime, or of manure. — The art of manuring. — How the colours of flowers may be changed.— Effect of culture upon wild plants.— The carrot, the cabbage, the turnip.— Garden fruits, flowers, and vegetables.— Origin of wheat and its varieties. — How these changes are produced.— Plants which follow the footsteps of man ; why they follow him.— Rapidity of growtli in favourable circumstances.— The yeast plant in grape juice — Manufacture of dry yeast — Chemical changes within the plant. — Production- of numerous peculiar substances—medicines, perfumes, and things useful in the arts.— The green of the leaf, and the poison of the nettle. — The covering of the ripe potato, apple, and young twig. — General purposes served by vegetation — It adorns the landscape ; in relation to dead nature, it purifies the atmosphere, produces vegetable mould, and forms deposits of combustible matter ; in relation to living

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CONTENTS.

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animals, it supplies subsidiary luxuries and comforts, but its main use is to feed them. — Numerous interesting chemical inquiries suggested by the natural diversities and different effects of the vegetable food consumed by herbivorous and omnivorous races 71

Chapter V. The Bread We Eat

The grain of wheat. — Bran and flour. — Separation of flour into starch and gluten. — Fermenting of dough. — Baking of bread. — New and stale bread. — Proportion of water in flour and in bread. — Composition of bread. — Bran richer in gluten. — Comparative composition. — Wheaten and rye bread compared.— Oatmeal and Indian-eorn meal. — Composition of rice. — Buckwheat, quinoa, Guinea corn, and dhurra. — Composition of beans, peas, and lupins.

— The sago palm, and the seeds of the araucaria. — The fruits of the banana, the date palm, the fig tree, and the bread-fruit tree. — Water contained in fruits and roots. — The turnip, carrot, and potato. — The composition of rice, the potato, and the plantain compared. — Deformity among the eaters of these three vegetables. — The Siberian lily. — The use of leaves as food. — The cabbage very nutritious. — Natural tendency of man to adjust the constituents of his food. — Irish ltol-cannon. — Starvation upon arrowroot and tapioca. — General characters of a nutritious diet. — National and individual influence of diet, 91

Chapter VI. The Beef We Cook

The fibrin and water of beef. — Composition of beef compared with that of wheaten bread and wheaten flour. — Striking differences.— Dried flesh compared with dried oat cake. — More fat in domesticated animals and such as are fed for the butcher. — Composition of fish — Richness of the salmon and the eel — Less fat in fowls — Eating butter with fish — Composition of the egg • — Albumen or white ; its properties and relations to gluten and fibrin — Oil in the yolk, and in the dried egg. — Composition of milk. — Milk allied both to animal and vegetable forms of food. — Milk a model food. — Importance of a mixed food containing much liquid.— Adjustment of the several ingredients of food in cooking. — Qualities of different kinds of cheese.— Composition of new and skimmed-milk cheeses. — Comparison with milk. — Cheese as a digester.— Solvent power of decayed cheese. — Customary practices in cooking. — Comparative value of different kinds of animal food. — Loss of beef and mutton in cooking. — Effects of heat upon meat. — Constituents of the juice of meat. — Kreatine. — Effects of salt upon meat. — Loss of nutritive value in salting. — How to boil meat and make meat soup. — Animal fats ; their analogy to vegetable fats. — The solid fat of beef, mutton, and palm-oil. — Composition of human fat, goose fat, butter, and the oil of the egg. — The liquid part of animal fat — Identity of animal and vegetable food as regards the mineral matters they respectively contain, ... 123

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Chapter VII. The Beverages We Infuse

THE TEAS.

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Artificial drinks nearly all vegetable infusions, with or without subsequent chemical changes. — Tea, extensive use of. — The tea-plant; how its leaves are gathered. — The aroma produced by roasting. — Mode of preparing green and black teas from the same leaves. — Principal varieties of green and black teas — Differences in fragrance and flavour. — Ancient use of tea in China and the adjoining countries — Introduction into Europe. — Total amount of tea produced— Consumption in the United Kingdom. — Sensible effects of tea. — Active chemical ingredients in tea. — The volatile oil, its action. — The theine, its composition — Occurs in coffee, in rnatd, and in guarana — Its effect in retarding the waste of the tissues. — Why tea is a favourite with the poor. —

The tannin, its properties and effects. — The gluten. — Tea-leaves and beans compared in nutritive quality. — Tartar mode of using tea. — Eating the exhausted leaves. — Tea varies in composition — Proportion extracted by water varies. — How tea is coloured or dyed green in China. — Lie tea. — Matd or Paraguay tea ; its ancient use in South America. — The Ilex Paraguayensis or matd tree, where it grows, and how its leaves are collected. — Gongonha of Brazil, a variety of matd. — Frequent use of inatfi, and its effects. — Composition of the leaf. — The volatile oil, the theine, the tannic acid, and the gluten.

— Coffee-tea made from the leaf of the coffee tree; use of this tea in the Eastern Archipelago ; effects observed from its use in Sumatra ; contains the same active ingredients as the leaves of the tea trees. — Labrador tea used in North America. — Abyssinian tea or chaat. — Tasmanian teas. — Faham tea. — Substitutes for Chinese tea and for mat£, 151

Chapter VIII. The Beverages We Infuse

THE COFFEES.

Coffee used in Abyssinia from time immemorial — Its introduction into Europe — Consumption in the United Kingdom, in Europe, and in the whole world. — Varieties of Coffee, and prices in the London market. — Effects of the infusion of coffee — It exalts the nervous life, and lessens the waste of the system. — Constituents of coffee. — The volatile oil, its production, mercantile value, and effects on the system. — The tannic acid, the theine or caffeine, and the gluten. — Composition of tea and coffee compared. — Loss of weight in roasting coffee. — Proportion of the roasted bean taken up by water very variable. — Substitutes for coffee. — Seeds of the water-iris, of the Turkish kenguel, of the roasted acom, of roasted corn and pulse, of roasted roots, and especially of chicory. — The chicory plant and root — How the root is prepared for use —

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CONTENTS.

Gives a fictitious appearance of strength to coffee.— Active ingredients in chicory— The empyreumatic oil, and the bitter principle— Its effects on the system.— Mode of detecting chicory in coffee.— Adulterations of chicory, . 197

Chapter IX. The Beverages We Infuse

THE COCOAS.

Cocoa, ancient use of, in Mexico— Brought to Europe by the Spaniards— The tree and its fruit— Varieties in the market— Quantity imported into this country— Manufacture of the bean.— Cocoa nibs.— Cocoa of Commerce.— Chocolate.— Constituents of cocoa— The volatile oil.— The peculiar bitter principle, theobromine.— The large proportion of fat which characterises cocoa. The starch and gluten. — Its general composition compared with that of milk.— It forms a most nutritious beverage — Substitutes for cocoa.— The earth-nut and the guarana of Brazil.— Decoction of cocoa nibs not so nutritious.—The cocoa husk or “ miserable ; ” importation of, and beverage made from.— General view of the chemistry of the infused beverages.— Summary of their physiological action.— Concluding reflections.— Prison dietaries, . 218

Chapter X. The Sweets We Extract

THE GRAPE AND CANE SUGARS.

Mineral sweets.— Vegetable sweets.— Number of these known to modern nations.

The grape sugars ; their sensible and chemical characters. — Honey sugars.

Trebizond honey.— Poisoning of Xenophon’s soldiers— Fruit sugars.— Starch or potato sugar, manufacture of. - Sugar from rags, from sawdust, and from Carrigeen, Ceylon, and Iceland mosses. — The cane sugars. — Spread of the sugar cane from Asia through Europe to America. — Varieties of the sugar cane.— Nutritive qualities of the raw cane-juice.— Extensive consumption of it.— Composition of the sugar cane.— Manufacture of cane sugar— Difficulties in the manufacture — Great loss of sugar in consequence. — Improvements in the manufacture, and their effects on West Indian prosperity. -Total produce of cane sugar in the world.— Consumption of sugar in the United Kingdom.— Sensible and chemical characters of cane sugar. — Beet or European sugar — Its importance on the continent of Europe. — Number and produce of the manufactories of France, Germany, and Russia.— Composition of the sugar beet — Difficulties in extracting the sugar — Progress of the manufacture — Its cliemico-agricultural relations. — Palm or date sugars — Quantity produced yearly.— Maple, or North American sugar — Quantity produced in Canada, New England, and New York — Mode of extraction. — Chemical changes in the maple sap. — Maize, or Mexican sugar ; manufacture of, in the United

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States, and in France. — Sorghum sugar, the cane of the north.— Total quantity of sugar extracted for use. — Chemistry in its economical and social relations, 238

Chapter XI. The Sweets We Extract

THE MANNA AND MILK SUGARS.

Manna sugars ; their sensible and chemical characters. — Manna of the ash ; its composition and uses. — Occurrence of manna sugar in sea-weeds. — Gum-tree manna. — Other mannas. — Oak, larch, and cedar mannas. — Persian manna. —

The alhagi and tamarisk mannas. — The manna of the Scriptures ; trees supposed to produce it. — The real manna not known. — Liquorice sugar. — Milk sugar.— Analogies in the composition of cane, grape, and milk sugar — How the two former are produced from each other, from starch, and from humic acid. — What chemists understand by chemical reactions — How a knowledge of these improves old and gives rise to new chemical arts. — Illustration in the manufacture of garancine, and the use of madder in dyeing, . . . 273

Chapter XII. The Liquors We Ferment

THE BEERS.

Our fermented drinks. — Grapo sugar is changed into alcohol by fermentation. — Cane sugar and starch converted into alcohol. — Production of diastase during the sprouting of corn. — Action of this substance upon starch. — How the infant plant is fed.— Malt liquors ; principles involved in the preparation of. — The malting of barley. — The making of beer. — Influence of diastase on the processes.—The fermentation of tire wort. — Influence of the yeast.— How the yeast plant grows and multiplies; its remarkable influence still inexplicable. — Composition of beer— Proportions of malt extract and of alcohol.— Beer characterised by its nutritive quality and its bitter principle. — Chica or maize beer of South America. — Maize malt. — Preparation of chica mascada, or chewed chica. — How the chewing promotes the process and gives strength to the chica.

— Influence of the saliva. — Chica from other vegetable substances. — Bouza or millet beer of Tartary, Arabia, and Abyssinia. — Murwa beer of Himalayas. — Chemical peculiarities of these millet beers.— Quass or rye beer. — Koumiss or milk beer ; mode of preparing it ; its composition and nutritious qualities. — Lactic acid in this beer. — A va, cava, or arva. — Extensive use of this drink among the South Sea Islanders ; how it is prepared and used ; its narcotic qualities. — Effect of chewing on the ava root. — Ceremonies attending its preparation and use in the Tonga and Feejee islands, . . . ggo

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CONTENTS.

Chapter XIII. The Liquors We Ferment

THE WINES.

rage

The wines. — Apple and pear wines. — Cider and perry — Differences in quality.

Varieties of cider apple. — Composition of cider ; tendency to sour. Grape

wines. — Rapid fermentation of grape juice. — Circumstances influence the quality of wine. — Composition of wine. — Proportion of alcohol in different wines ; proportion of sugar. — Tartaric acid the peculiar acid of grape wine — Proportions of acid in different wines. — CEnanthic ether gives the vinous flavour to wines. — Peculiar odoriferous principles which impart to each wine its own flavour or bouquet. — Consumption of wine in the United Kingdom. — Palm wine or toddy — How extracted from the cocoa-nut tree, and from the date tree. — Extensive use of palm wine. — Sugar-cane wine, or guarapo. — Pulque, or agave wine, 313

Chapter XIV. The Liquors We Ferment

• THE BRANDIES.

The brandies, or ardent spirits.— Methods of distillation. — Absolute alcohol.— Strength of different varieties of spirits. — Peculiarities in the preparatory processes of the distiller. — Use of raw grain mixed with malt : profit of this. —Average produce of proof spirits.— Peculiar flavours of cognac, rum, &c. — Consumption of home-made ardent spirits in the three kingdoms. — Quantity of malt used in brewing.— Spirits consumed in the form of beer.— Comparative sobriety of England, Scotland, and Ireland. — Consumption of foreign liquors. — Alleged greater intemperance of Scotland and Ireland : how this impression has been produced.— Influence of the nutritive matter, and of the hops contained in beer.— Influence of general food and temperament.— Ardent spirits serve the same purpose as the starch and fat of our food, and retard the waste of the body.— Wine, “ the milk of the aged.”— Substances employed to give a fictitious strength to fermented liquors 330

TIIE

CHEMISTRY OF COMMON LIFE.

Chapter I. The Air We Breathe

Height of the earth’s atmosphere ; it is one of the elements of the ancients — Composition of the atmosphere. — Oxygen, preparation and properties of. — Nitrogen, preparation and properties of. — Proportions of these elements in the air ; their adaptation in kind and quantity to the existing condition of things. — Uses of the oxygen and nitrogen. — Uses of the carbonic acid ; its importance to vegetable life.— Deleterious influence upon animal life. — The “Poison Valley” of Java. — Importance of the watery vapour of the air; its constant circulation. — Formation of rain and dew ; their many uses. — Accidental constituents of the air; ozone, nitric acid, and ammonia. — Vapours which rise from the surface of the earth, and saline matters from the sea.

The earth we inhabit is surrounded by an atmosphere of air, the height of which is known to be at least forty-five miles. It presses upon the earth with a weight equal at the level of the sea to about 15 lb. on every square inch of surface. As we ascend high mountains, this weight becomes less ; and as we go down into deep mines, it becomes sensibly greater.

We breathe this atmospheric air, and without it we could not live a single moment. It floats around the

VOL. I.

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THE AIR WE BREATHE.

earth in almost perpetual motion ; and according to the swiftness with which it moves, it produces gentle breezes, swift winds, or terrible tornadoes.

Though very familiar to us, and regarded with little curiosity, this air is yet very wonderful, both in it self and in its uses. Imperfect as the knowledge of the ancients was, they recognised its importance by giving it a place among what they regarded as the four primal elements of nature — fire, air, earth, and water.

Yet, though apparently pure and elementary, it is by no means either a simple or pure substance. It is a mixture of several different kinds of matter, each of which performs a beautiful and wise part in relation to animal and vegetable life. Four substances, at least, are known to be necessary to its composition. Two of these, oxygen and nitrogen, form nearly its entire bulk ; the two others, carbonic acid and watery vapour, being present only in minute quantities.

Oxygen is a kind of air or gas, which, like the atmosphere itself, is without colour, taste, or smell. A candle burns in it with much greater brilliancy and rapidity than in common air. Animals also breathe in it with an increase of pleasure ; but it excites them, quickens their circulation, throws them into a state of fever, and finally kills them, by excess of excitement. They live too rapidly in pure oxygen gas, and burn away in it like the fast-flaring candle.

This gas is easily prepared by mixing the chlorate of potash of the shops with a little sand, powdered glass,

OXYGEN GAS.

or oxide of manganese, and heating the mixture in a flask over a spiritlamp. When it melts, the gas is given offi and will soon fill the flask. It cannot be seen by the eye, or detected by any of the other senses. Its presence may be readily shown, however, by introducing a lighted taper, or a bit of red-hot charcoal, or of kindled phosphorus at the end of a wire (fig. 1). The brilliancy of the burning will prove the presence of the gas.

Nitrogen is also a kind of air which, like oxygen, is void of colour, taste, Eig. 2.

and smell ; but a lighted candle is instantly extinguished, and animals cease to breathe when introduced into it. We obtain this gas by putting a bit of phosphorus into a small cup over ■water, kindling it, and inverting over it a bottle, dipping with its mouth into the water (fig. 2). When the phosphorus has ceased to burn,

THE AIR WE BREATHE.

and the bottle has become cool, it may be corked and

„ removed from the

Fig. 3.

water. If a lighted taper be now introduced into the bottle, it will immediately be extinguished, showing that only nitrogen remains (fig. 3).

In this process the burning phosphorus removes the oxygen from the air

contained in the bottle, and leaves only the nitrogen. Oxygen is one-ninth part heavier, and nitrogen one

thirty-sixth part lighter, than common air.

Carbonic acid is a kind of air which, like oxygen and nitrogen, is void of colour ; but, unlike them, possesses a slight odour, and a perceptibly sour taste.

Burning bodies are extinguished, and animals cease to breathe, when introduced into it. It is one-half heavier than common air, and can therefore be poured through

CAKBONIC GAS.

the air from one vessel to another (fig. 4). When passed through lime-water,* it makes it milky (fig. 5), forming with the dissolved lime an insoluble white powTder, which, because it contains carbonic acid, is called carbonate of lime, and is the same thing as chalk. It is the escape of this gas which gives their sparkling briskness to fermented liquors, to soda-water, and to the waters of some mineral springs.

Carbonic acid is easily prepared by pouring vinegar upon common soda, or diluted spirit of salt (muriatic acid) upon chalk or limestone. The gas rises in bubbles through the liquid, and, in consequence of its weight, remains in the lower part of the vessel. As it collects it gradually ascends, driving the common air before it, and at last flows, as water would do, over the edge of the vessel.

Its rise may be shown by introducing two lighted tapers, as in the figure (fig. 6), when the lower one will be seen to go out, while the upper one is still burning.

* Lime-water is formed by pouring water upon slaked lime, shaking them well together, and allowing the mixture to settle. The clear liquid contains a portion of the lime in solution, and is therefore called ime-water.

Fig. 5.

THE AIR WE BREATHE.

By watery vapour is meant the steam or vapour, visible or invisible, which ascends from a surface of water when exposed to the air. When water is spilt upon the ground in dry weather, it soon disappears : it rises in invisible vapour, and floats buoyantly among the other constituents of the atmosphere.

These four substances the air everywhere and always contains, and always in very nearly the same proportions. Thus Gay Lussac examined air collected at a distance of four miles from the earth’s surface, and comparing it with air collected from the summit of the Alps, and from towns and villages, found no sensible difference. In 1852, Mr Welsh, under the direction of the British Association, examined air collected at an elevation of 18,000 feet above the earth, and, comparing it with air collected from the surface, found the one to contain 20.88 per cent of oxygen, the other 20.92. The four substances we have just mentioned are all necessary to the daily wants of animal and vegetable life ; but two of them, oxygen and nitrogen, form so large a proportion of the whole that we are accustomed to say of dry air, that it consists of nitrogen and oxygen only, in the proportion of 4 gallons of the former to 1 of the latter. More correctly, however, air, when deprived of the watery vapour and carbonic acid it contains, consists, in 100 gallons, of 79 of nitrogen mixed with 21 of oxygen ; or of —

>T. By measure.

Nitrogen,

HOW GASES MIX IN THE AIR.

It lias been calculated that the atmosphere of our globe contains 2,551,586 billions of pounds of oxygen ; and the yearly consumption of this oxygen, in the respiration of men and animals together with the processes of ordinary combustion, amounts to two and a quarter billions of pounds. Thus, in a hundred years the consumption would only reach 220 billions — that is, not even the ten-thousandth part of the whole.

The carbonic acid exists in the air in very small proportion. At ordinary elevations there are only about 2 gallons of this gas in every 5000 of air — -^-g^th part of the whole. It increases, however, as we ascend, so that at heights of 8000 or 10,000 feet the proportion of carbonic acid is nearly doubled. Even this increased quantity is very small ; and yet the presence of this gas is essential to the existence of vegetable life on the surface of the earth.

But being heavier than common air, it appears singular that the proportion of this gas should increase as we ascend into the atmosphere. Its natural tendency would seem to be rather to sink towards the earth, and there to form a layer of deadly air, in which neither animal nor plant could live. But independent of winds and aerial currents, wdiicli tend to mix and blend together the different gases of which the air consists, all gases, by a law of nature, tend to diffuse themselves through each other, and to intermix more or less speedily, even where the utmost stillness prevails and no wind agitates them. This is the “ law of the diffusion,” discovered by Graham, according to which heavy gases intermix with light

THE AIR WE BREATHE.