The clear liquid containing the non-volatile acids and other bodies was further concentrated and made up to 500 c.c.; it was dark brown in colour and was very acid to litmus; owing to a trace of flocculent matter, it was again filtered. The presence of lactic acid was shown in the following manner: 10 c.c. of the liquid were placed in a small distilling-flask along with 2 c.c. strong H_{2}SO_{4} and about 0·5 grm. potassium chromate in a little water. This was distilled and the vapours received in a test-tube surrounded by cold water; on adding magenta solution, decolorised by SO_{2}, to the liquid in the test-tube, a red colour was produced by the aldehyde formed from the lactic acid; aldehyde was also recognised by its smell. We find this an exceedingly delicate test for lactic acid, and as far as we know it is quite new in this form. For 10 c.c. of liquid to be examined, we find 2 c.c. strong H_{2}SO_{4} and 1 grm. of potassium chromate to be the best proportions. Formic, acetic, propionic, butyric, valerianic, succinic, malic, tartaric, and citric acids do not give the reaction. The liquid was now tested for _succinic_ and _malic_ acids. 25 c.c. was taken and decolorised by treatment with pure animal charcoal for half an hour; the liquid was then filtered, the charcoal washed free from acid, and the filtrate concentrated; ammonia was added in slight excess, the precipitate of calcium phosphate filtered off. To the filtrate CaCl_{2} was added in slight excess to remove the remainder of phosphates, the liquid filtered, and the filtrate cautiously neutralised with HCl; the addition of neutral ferric chloride to a portion gave no precipitate, showing the _absence of succinic acid_. To the remainder an equal volume of absolute alcohol was added and the liquid boiled; there was no precipitate. Twice the volume of absolute alcohol was then added and gave no precipitate. On the addition of four times the volume of absolute alcohol, a slight white precipitate came down, which evidently consisted of dextrin, from the manner in which it settled round the sides of the tube, and from its insolubility on adding HCl. We therefore conclude that there is no malic acid present, and that the only non-volatile acid produced is _lactic acid_. The acidity was first determined by titrating 10 c.c. of the solution with N/10 sodium hydrate, using glazed litmus paper to determine the point of neutralisation. The 10 c.c. required 6·66 c.c. N/10 NaOH, equivalent to 0·666 of N lactic acid = 0·7481 grm. per litre of original drench.