The paper which one of us had the honour of reading before this Section on December 11, 1890,[161] dealt chiefly with methods of bacteriological research, but especially in connection with the fermentation of bran as applied in the manufacture of light leathers. The object of the present paper is to give an account of further research into the nature of the fermentation and its products, the former communication being very incomplete. In further investigating the matter, we endeavoured-- [161] J.S.C.I., 1890, 27. 1. To obtain a complete knowledge of the products of the actual fermentation as it takes place in practice. 2. To discover in what way the ferment acts, both on the materials fermenting and on the skins. 3. To examine in the same way the products of a pure cultivation of the bacterium causing the fermentation. 1. *The Products of the Actual Fermentation.*--These may be divided into three groups:--(1) gases; (2) volatile bodies; (3) non-volatile bodies. It was stated in the former paper that the ferment produced an inflammable gas along with considerable quantities of CO_{2}, H_{2}S, etc. The inflammable gas was thought by analogy from the researches of Tappeiner[162] to be methane; it has, however, proved to be pure hydrogen. The absence of hydro-carbons was shown by the following method. Some of the gases were collected, the CO_{2} and SH_{2} removed by absorption with KOH, and the remaining gases exploded in a eudiometer tube with oxygen. The gases which remained after explosion did not diminish in volume after standing over KOH solution, showing absence of the paraffins and olefines. [162] Zeits. für Biologie, xxiv. 105. For the purpose of analysis, about 1-1/2 litres of the gas were collected at a time in a large flask, fitted with a caoutchouc stopper and a funnel having an area of 28 sq. in. This was inverted, filled with the drench liquid, over the vat. The gas when collected was transferred immediately in the vat to a glass-stoppered bottle, sealed with a small quantity of the fermenting liquid and examined at once. Nine analyses have been made, most of them in duplicate. The following table, p. 248, gives the results of three of these duplicate analyses, which have been performed by Hempel’s method, the hydrogen being estimated by combustion in air over heated palladinised asbestos. We find that the gases given off during the fermentation are practically the same, with or without skins. ---------------------+------+------+------ Gases | A | B | C ---------------------+------+------+------ CO_{2} and H_{2}S | 21·9 | 25·2 | 42·4 O_{2} | 1·0 | 2·1 | 3·6 H_{2} | 53·1 | 46·7 | 28·2 N_{2} | 24·0 | 26·0 | 25·8 ---------------------+------+------+------ A is from a vat containing no skins, 1–2 days. B from a vat containing skins, 2–3 days. C from a vat containing skins, 3–4 days.