was repeated several times, till it was sufficiently purified. The malate of lime would now be found in the precipitate with alcohol, but tannate of lime, gypsum, &c., might likewise exist. It was dissolved in water, sugar of lead added, and then filtered (a).

The precipitate, with acetate of lead, was then suspended in water, sulphuretted hydrogen conducted through it, the sulphide of lead filtered, the liquid warmed in order to expel sulphuretted hydrogen, and then cooled again: it was then fully saturated with milk of lime, the liquid filtered and neutralized with acetic acid. No tannic acid could be now found in it, but if malic acid exist in the wine, malate of lime was present.

All the tests which have been hitherto applied to malate of lime confirm its presence, and we therefore assume that a small quantity of malic acid is contained in red Bordeaux.

The liquid (a) which was separated from the precipitate of lead was first freed from lead by sulphuretted hydrogen; it contains a considerable amount of gum, which may be precipitated by alcohol. No copper could be reduced by the substance still remaining in the liquid, when a test solution of oxide of copper and potass was used, unless it had been previously warmed with hydrochloric acid, then a considerable precipitate was obtained. With the exception of acetate of lime, no other distinguishable substances remain in the liquid.

CHAPTER XV.

GLUCIC ACID.

By adding

THE experiments tried by Graham, Hoffmann, and Redwood, show that, besides carbonic acid and alcohol, another substance is formed during the fermentation of sugar which is no longer capable of fermenting, and is compared by them to glucic acid. 1, 2, and 3 per cent., by volume, of wet yeast, to a solution of sugar, they obtained 4.4, 3.72, 3.7 per cent. of this substance, and more might have been procured, had a larger quantity of yeast been employed. By filtering and evaporating the liquid this substance was obtained as a dark brown matter, of the nature of extract, which had a bitter taste, and owing to the lactic acid contained in it, was acid. More than one substance was discovered in it, but no sugar, although it was able to reduce oxide of copper to a sub-oxide.

Thénard has already recognised this substance, and says, that when he allows sugar to ferment with a large quantity of yeast, he always obtained 4 per cent. of the sugar thus employed as an extractive matter.

* Liebig u. Kopp, Jahresber, 1852, s. 801.

4 per cent. comes very near the 3.7 per cent. given by the above-mentioned chemists.

If glucic acid be really present in wine, and the wine be treated in the manner described (p. 248), the acid will be found in the liquid which has been filtered from the lime salt precipitated by alcohol. If the glucic acid be saturated with caustic potassa, it combines with it and forms a neutral salt, which is insoluble in alcohol; but if, as was the case here, it be saturated with chalk, an acid salt is formed, from which no precipitate can be formed by alcohol. The alcoholic liquid, separated from the neutral salt, contains not only all such acid glucate of lime as may be present, but likewise the sugar of the wine, nearly all the tannic acid, and such other substances as, under these circumstances, are soluble in alcohol.

The alcohol was distilled, the residue dissolved in water, and precipitated with basic acetate of lead, which gave rise to a copious precipitate.

After the lead had been removed from the liquid, which was drawn off, the presence of sugar was indicated by the copper test.

The precipitate of basic acetate of lead was suspended in water, sulphuretted hydrogen conducted through it, the liquid warmed in order to expel sulphuretted hydrogen again, milk of lime added in order to separate the tannic acid which was present in large quantity as a basic lime salt. The liquid was filtered, carbonic acid conducted through it, then warmed, and

again filtered in order to remove the chalk. If glucic acid were contained in the wine, we should find it here. Sugar could no longer exist. The liquid when warmed with test solution of oxide of copper and potash showed no reduction, therefore no glucic acid was found in red Bordeaux wines.

I do not, however, venture to assert that no glucic acid exists in wine; on the contrary, knowing how quickly and easily the sugar in wine (which is so liable to undergo change) may be resolved into glucic acid, I consider it highly probable it does exist. But glucic acid, even when combined with lime, may very easily be resolved into apoglucic acid, and then masked by the colouring matters of the wine. I shall speak again of this matter in treating of the decomposition of wine; I do not therefore deny that glucic acid is present in wine, but it is difficult to prove it.

CHAPTER XVI.

FORMIC AND LACTIC ACIDS.

THESE two acids have not yet been mentioned, for although their presence in wine may be justly suspected it has not yet been proved.

I have not been able to detect formic acid in Port, Madeira or Teneriffe wines by distillation, and when nitrate of silver and a little ammonia were added to the distillate no silver was reduced. No brown colour was produced by means of caustic potash, so we may conclude that no aldehyde is present in it.

With respect to lactic acid, lactate of lead is soluble. Lactic acid must therefore be sought in the liquid obtained by precipitating the wine with sugar of lead, basic acetate of lead, and ammonia, and then filtering.

When this liquid (obtained from red Bordeaux) has been freed from lead by sulphuretted hydrogen, filtered and evaporated, the residue is easily soluble in alcohol. This deposit, in which there was a good deal of sugar, was digested with carbonate of zinc upon a water bath, and freed with alcohol from sugar and