and in the course of several years sinks down to a few tenths of a per cent. or so, and the wine is then fit for bottling. It is only in rare cases that a natural wine can be safely bottled when it contains more than 1% of sugar.

Fortified wines, the fermentation of which has been stopped by the addition of spirits, generally contain more sugar, ranging from 0 to 5%, and in a few liqueur wines rising even to upwards of 25%. The amount of sugar found in these wines depends, firstly, upon the amount left when fermentation was stopped; and, secondly, upon the quantity added, as so-called saccharine, to the finished wine, this latter being very frequently done in this country. Sometimes also, a portion of evaporated must, which has not been subjected to any fermentation, is added to the fortified wine. It is on this property of the spirit of preventing the fermentation of sugar that its chief use to the wine grower and merchant depends, as it makes even young wine at once a marketable article. The buyer is then obliged to keep the wine for many years in his cellar, to allow the injurious effects of the added spirit to disappear, and let the wine once more become a pleasant drink.

In all pure or simply fortified wines by far the greater proportion of the sugar present is, as before explained, fruit sugar, the rest being grape sugar; in such, to which inspissated must or a solution of cane sugar (saccharine) has been added, the proportion of grape sugar is greater, though still bearing the fruit sugar in excess. In wines in the preparation of which sugar of starch has been employed grape sugar is the predominating kind.

Compound Ethers.-We have before seen that whenever an alcohol (or several alcohols) and an acid (or several acids) are mixed, the formation of what are termed compound ethers commences. A compound ether may be looked upon as a salt of an acid, with an alcohol radical analogous to the ordinary mineral salts of the acid.

Or, expressed in words, hydrate of potassium (potash) and acetic acid yield acetate of potassium and water; and hydrate of ethyl (alcohol) and acetic acid yield acetate of ethyl (acetic ether) and water.

The production of compound ethers commences as soon as the acid and alcohol come together; it takes place rapidly at first, very slowly towards the end. If water be absent, and the water produced during the reaction is removed, the process goes

on until either the whole of the acid or the whole of the alcohol has been converted into compound ether. The presence of water, however, prevents this complete etherification; the more water present, the smaller the proportion of ether formed from a given quantity of alcohol and acid. Under these circumstances, then, the amount of alcohol converted finally into compound ether depends upon the proportion of alcohol, acid, and water present, but is independent of the nature of the alcohol and acid.

Whatever be the proportion in which these three substances are mixed, after the lapse of a longer or shorter time there will have been produced a certain amount of compound ethers, the rest of the alcohols and acids remaining free; beyond this no more ether will be found, however long the mixture may be kept. If, after this stage of equilibrium has been reached, the relative proportion of the different substances is altered-if, for example, alcohol be added, or the acid be increased—more ether will begin to be formed; if, on the other hand, alcohol or acid is removed, or water is added, some of the compound ether already formed will begin to be decomposed, until, in either case, equilibrium is once more established.

By means of a formula given by Berthelot, the amount of alcohol contained in the compound ethers of any mixture of alcohols, acids, and water, when etherification is complete, can be calculated, whilst, by a process elsewhere described by the author, the amount actually so present at any time can be estimated. As long, then, as the amount found falls below the amount calculated, etherification is not yet completed; when both agree, equilibrium has been established.

As regards the formation of compound ethers, wine may be looked upon as a mixture of several alcohols and acids with water, and all the foregoing rules will be applicable to it. The estimation of the alcohol contained in the compound ethers of a wine, coupled with the calculated amount, will thus, among other things, give us some information as to the age of the wine. In young wines the amount found will fall below, in older or old wines it will agree with, the calculated amount.

Wines of no very great alcoholic strength have generally arrived at the stage of equilibrium, as regards the formation of compound ethers, in from four to six years; in the case of strong wines, ten years and upwards are required. The conditions under which the wine is kept will, however, greatly influence this time; thus a high temperature promotes, a low temperature checks, the production of ethers.

As previously explained, wine contains both fixed and volatile acids, and these give rise to fixed and volatile compound ethers respectively; that is, such as cannot, and such as can, be dis

tilled without decomposition. The amount of alcohol contained in the whole number of either class of compound ethers present can be estimated, but the determination of each individual compound ether cannot as yet be accomplished. Fixed ethers have, comparatively speaking, little influence on the character of the wine beyond neutralising part of the acid and facilitating the production of volatile ethers. Among volatile ethers, on the other hand, there are many possessing a very characteristic, and often, especially when much diluted, very agreeable smell; and to them the wine owes a great part of its flavour and bouquet, and probably also some of its exhilarating and stimulating effects.

As regards the proportion existing between the amounts of volatile and fixed ethers present, all pure natural wines, hitherto examined in this respect, contained a greater proportion of volatile than fixed ethers, in spite of the great preponderance of fixed acids; nearly all fortified wines, on the other hand, contained a greater proportion of fixed ethers, although the proportion of volatile acids is generally higher than in the former. Sherries and Madeiras, however, although undoubtedly fortified, form an exception to this rule; they contain, like the natural wines, more volatile than fixed ethers. Lastly, it appears that as the fortified wines get older, the proportion of volatile ethers becomes greater, so that at last they equal, or even exceed, the fixed ethers in amount, the wine gradually coming round to the natural standard.

It seems very desirable that medical men should direct their attention to this difference among wines. By selecting, for example, such wines as contain the highest proportion of volatile ethers relative to their alcoholic strength, it may sometimes be possible to produce the desired stimulating effect with the minimum amount of disturbance often following the administration of alcohol.

The total amount of compound ethers present in any wine is extremely small. Thus in the highest case yet found (a Madeira, which had been 50 years in bottle) the alcohol contained in the compound ethers of the wine (both fixed and volatile) amounted to only one part in 800 parts of wine—equivalent, roughly speaking, to about one part of compound ether in 300 parts of wine.

Glycerine and Succinic Acid.-As previously explained, 107 parts of cane sugar, when submitted to fermentation, yield, according to Pasteur, about 3.6 parts of glycerine and 0-60 parts of succinic acid; all fermented liquids should therefore contain small quantities of these two substances. At present, little is known as to the amounts actually present in different sorts of wine. Succinic acid is probably without much

influence on the character of the wine. Glycerine, however, besides being present in larger quantity (about one fourteenth part of the amount of alcohol) has a well marked sweetish taste, and may account for the like taste possessed by many wines that are perfectly free from sugar. Besides this, it seems to mitigate the harshness of taste belonging to several of the other constituents of the wine, and thus to render it milder than it otherwise would be. On account of these properties, and not being liable to fermentation, it is now used extensively for the adulteration of wine.

Albumenoid Substances.-Grapes contain a not inconsiderable amount of some albumenoid substance which, like all such, is extremely liable to decomposition, and to induce decomposition in other substances in contact with it. Accordingly, when exposed to the action of the air by the crushing of the berry, it absorbs oxygen and yields the ferment under the influence of which the sugar is transformed into carbonic acid and alcohol, whilst the latter may even be converted into acetic acid, the ferment, or yeast, absorbing the albumenoid substance and, by rendering it insoluble, removing it from the wine. In all white wines, properly fermented, this albumenoid substance is almost entirely absent, having been precipitated during fermentation. Such wines are accordingly but little liable to further change. In imperfectly fermented wines, on the other hand, some albumenoid substance remains dissolved, rendering the wine liable to fresh fermentation if not protected by an addition of spirit. All red wines, owing to their having fermented on the husks, contain, when young, much albumenoid substance, which, however, in their case, is preserved from change by the tannin present. In the course of time the greater part of it is thrown down with the colouring matter and tannin.

Mineral Substances, or Ash.-When wine is evaporated, and the dry residue left is heated for some time to a dull red heat, there remains a greater or smaller proportion of mineral constituents, called ash. The nature and quantity of ash left by a wine is one of its most characteristic features. Generally speaking, the total amount of ash ranges in pure natural wines between 1.5 and 2.5 parts per thousand. Under normal conditions this ash consists of carbonate, sulphate and chloride of potassium, chloride of sodium, phosphate and carbonate of calcium, with traces of silica, magnesia, and iron; frequently there are also minute traces of lithium, and sometimes of manganese. In many southern countries it is the custom to add plaster of Paris to the must; one effect of this addition is a great increase

* This carbonate is not contained as such in the wine, but is produced by the decomposition of a salt of potassium with an organic acid, such as the tartaric or malic acid, during ignition.

in the proportion of ash, owing to the production of sulphate of potassium. Sulphate of calcium (plaster of Paris) and cream of tartar give rise to the production of tartate of calcium (insoluble), sulphate of potassium, and sulphuric acid; and in wines so treated the ash rises frequently to five parts and more per thousand, consisting almost entirely of sulphate of potassium. The ash of these wines is frequently free from carbonates and chlorides, because the small quantity of sulphuric acid produced, as above explained, expels the weaker and volatile acids in the course of evaporation and incineration. No wine is met with free from chlorides.

Total dry Residue and Extractives.-If a quantity of wine be carefully evaporated on a water-bath, a greater or less proportion of dry residue is left which contains all those constituents not volatile at 100°C. The greater part of this residue usually consists of sugar, acids, mineral constituents, &c.; but in all genuine wines there is always, in addition, a small proportion of substances the exact nature of which is not at present known, and therefore do not as yet admit of quantitative estimation. Accordingly, if from the total dry residue left all those substances admitting of estimation are subtracted, a small amount will be left unaccounted for. This consists of what are generally termed extractives. No genuine wine is free from these extractives; they may therefore form a valuable feature for distinguishing the true from the factitious article. In wines free from sugar these extractives frequently constitute the greater part of the total residue.

In pure natural wines the total amount of dry residue varies generally between fifteen and thirty parts per thousand. In fortified wines this total residue frequently rises to sixty, eighty, or even more per thousand; it ranges generally between twenty and sixty parts, a great proportion of the residue in these cases being sugar.