And yet each of these three substances is very different in its properties from either of the other two.

Again, the dark-brown vegetable matter (humic acid) to which the colour of soils is partly owing, consists of carbon and water only, for

86 of carbon, and 27 of water, form 68 of humic acid.

Now, in regard to substances so composed, it is not difficult, with the aid of this knowledge, to form a general idea of the way in which they may be transformed, one into the other. Thus

63 of humic acid united to 18 of water, may form 81 of cellulose, starch, gum,

or sugar.

81 of starch, with 9 of water, may form 90 of cane sugar.

90 of cane sugar, with 9 of water, may form 99 of grape sugar.

Thus

And changes of this kind really take place in nature. the humic acid of the soil enters the roots of plants, and in the interior of the plant is changed into the cellulose or woody matter of its growing shoots, and into the starch of its seeds. The starch of the tasteless pear, of the banana, and of the bread fruit (p. 96), changes into sugar as the fruit ripens and becomes sweet. And by the action of acids in the sour saps of plants, and in somewhat acid fruits, cane sugar, which is first produced, is changed into grape sugar. In all these cases, the substance which disappears only combines with a little more water, to form the new compound which is produced.

And we artificially imitate these natural operations when, in the manufacture of potato sugar, we transform the starch of the potato into a sweet resembling the sugar of grapes, or when, by the prolonged action of sulphuric acid, we change sawdust or rags into a similar sweet.

In these changes, the acid employed possesses the singular property of causing the carbon of the starch or woody fibre to unite with a larger proportion of the elements of

water, and thus to assume the form of grape sugar. And it is out of such observed reactions of bodies-as such influences are called-that new chemical arts are daily springing up. Thus the manufacture of potato sugar, already described, is a valuable independent art, founded solely upon a knowledge of this action of sulphuric acid. But many other arts, besides, have been either wholly based upon, or have been greatly improved, by the application of this property. I instance only the manufacture of a dye-stuff called garancine.

Madder, as is well known, is the root of a plant (Rubia tinctorum) which is cultivated largely in certain parts of Europe, and the Levant, for the sake of the beautiful red colours it gives to the fibres of cotton and wool. This root, when dried and ground to fine powder, is the common madder of the dyer. But, besides the valuable colouring matter, this root contains gum, gluten, mucilage resembling that obtained from Iceland moss, and various other substances, which interfere with its use as a dye, and render the use of it difficult to the dyer, and the colour it imparts in some degree uncertain. In the course of the many chemical in. vestigations to which this substance has been subjected, however, it was observed, that while sulphuric acid, under certain circumstances, acted upon nearly all these useless parts of the root, it had no effect upon the colouring matter. The former it changed into easily soluble sugar, or altogether destroyed; while to the latter it only gave new brightness and beauty. The application of this was obvious. The ground root was steeped for so many hours in sulphuric acid mingled with so much water, and was then washed perfectly free from acid, and again dried. It was now the colouring matter, or garancine, comparatively pure-in some cases 5, but usually about 3 times more powerful as a dye than the natural root. It was less bulky and lighter

for carriage in proportion, was more easy to use, and more certain in the shades of colour it gave to cloth.

Thus, from the application to madder root of the observ ed action of sulphuric acid upon vegetable substances allied to our sugars, arose both the new art of making garancine, and important improvements in the old art of dyeing.

Thousands of similar reactions are known to chemists; and the origin of almost every art of life may be traced to the first observation of some one of the countless visible influences which one form of matter exercises over another.

Melted soda dissolves sea-sand, and the solution, when cold, is our common window-glass. Hence the magnificent glass-trade of our time.

Potash melted with hoofs and horns, and thrown carelessly into water containing iron, gave an intense blue colour. This was Prussian blue; and hence a crowd of arts and manufactures, and of beautiful applications of chemistry, have sprung up.

Every day new arts sprout up, as it were, beneath our feet, as we linger in our laboratories observing the new reactions of probably new bodies; and in each new art is seen a new means of adding to the comforts and luxuries of mankind, of giving new materials and facilities to commerce, and of increasing the power and resources of nations.

For pleasing examples of such arts-just bursting into leaf like the buds before our eyes in the sunshine of our English spring-I refer the reader to a succeeding chapter on THE ODOURS WE ENJOY.

CHAPTER XII.

THE LIQUORS WE FERMENT.

THE BEERS.

Our fermented drinks.-Grape 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 the 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 characterized 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 the 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.-Ava, 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.

THE liquors we ferment are all directly produced, either from the natural sugars which we extract from plants, or from the sugars which we prepare by art. I shall briefly advert to the most interesting and important of these liquors now in use in different parts of the world. The way

in which these drinks are prepared, their chemical composition, and their chemico-physiological action upon the system, are more or less connected with the common life of almost every people.

I. THE BEERS.-When grape sugar is dissolved in water, and a little yeast is added to the solution, it begins speedily to ferment. During this fermentation, the sugar is split up into three different substances-alcohol, water, and carbonic acid. The two former remains in the liquid while the carbonic acid gas escapes in bubbles into the air.

When common cane sugar is dissolved in water and mixed with yeast in a similar way, fermentation is induced as before. The cane sugar is first changed into grape sugar by the action of the yeast, and then the grape sugar is split up into alcohol, water, and carbonic acid. These changes take place in close as well as in open vessels, so that the presence of air is no way necessary to their perfect and rapid completion.

If starch be converted into grape sugar by the action of diluted sulphuric acid, or of a mixture of malt, as described in a preceding chapter, and yeast be then added to the sweet solution, the same changes and the same production

*

So that the substance of one of grape sugar is split up into two of alcohol, four of carbonic acid, and two of water. This splitting up is induced by the yeast, which, however, affords none of the materials of which the alcohol, &c., consists.

* THE SWEETS WE EXTRACT, p. 197.