----------+-----------+-----------+------------- Fraction |Formic Acid|Acetic Acid|Butyric Acid ----------+-----------+-----------+------------- I. | .. | 0·46070 | 0·1488 II. | 0·03980 | 0·42040 | .. III. | 0·3143 | 0·20710 | .. IV. | 0·1539 | 0·1201 | .. ----------+-----------+-----------+------------- Totals | 0·5080 | 1·2083 | 0·1488 ----------+-----------+-----------+------------- The total volatile acids produced amounting to 1·8651 grm. The residual liquid containing the non-volatile acids was submitted to the test for lactic acid previously used,[179] and it was found to be present. [179] J.S.C.I. 1893, 424; vide supra, p. 254. The method employed for estimating lactic acid in our previous communication proving somewhat difficult, we endeavoured to improve it by extracting the concentrated solution of the non-volatile acids on prepared pumice stone with ether in a paper thimble contained in a Soxhlet fat-extraction apparatus. After repeated trials we found that this method did not give accurate results. The solution was therefore titrated with 1/10 N sodium hydrate, using glazed litmus paper to determine the point of neutralisation. The acidity found corresponded to 2·438 grm. of lactic acid per 1000 c.c. of the fermented liquid. We have done several other fermentations with this organism and find the same acids produced and the same gases evolved, the results just given being fully confirmed. At the same time the amount of the acids produced and their proportions vary, that is to say, the quantity of acid from a given fermentation cannot be predicted with absolute accuracy, although the conditions under which we carried out the experiments were made as like as possible. We give the total acids from four fermentations to show the amount of variation. I. is a symbiotic fermentation caused by organisms α and β; the remainder are fermentations by α alone. ---------------------------+---------+---------+---------+--------- Fermentation | I | II | III[180]| IV ---------------------------+---------+---------+---------+--------- Total vol. acids, grm. per | 2·4968 | 1·8651 | 0·9738 | 1·5636 1000 c.c. | | | | | | | | Mean percentage BaSO_{4} | 89·17 | 91·76 | 95·4 | 93·6 from Ba salts of vol. acids| | | | | | | | Lactic acid | 8·9500 | 2·4380 | 1·4737 | 2·9700 ---------------------------+---------+---------+---------+--------- COMPARISON OF ACIDS FROM FERMENTATION II. AND III.[180]