Studies on fermentation : the diseases of beer, their causes, and the means of preventing them . eof the tubes is fitted a kind of muff or bag, composed of a cylin-drical cage of metallic gauze, over which a layer of well-combedcotton wool is placed, the whole being covered with a muslinbag. The object of this arrangement is to act as an air-filter forretaining the particles of dust. When fermentation has com-menced in the apparatus, we have simply to press momentarilj-the india-rubber connection between the tube from the lid andthe tube with the bag. This will at once cause a regular streamof
Studies on fermentation : the diseases of beer, their causes, and the means of preventing them . eof the tubes is fitted a kind of muff or bag, composed of a cylin-drical cage of metallic gauze, over which a layer of well-combedcotton wool is placed, the whole being covered with a muslinbag. The object of this arrangement is to act as an air-filter forretaining the particles of dust. When fermentation has com-menced in the apparatus, we have simply to press momentarilj-the india-rubber connection between the tube from the lid andthe tube with the bag. This will at once cause a regular streamof carbonic acid to issue from the end of the uncovered tube,whilst the air will enter by the filtering tube to take its place ;and this arrangement will be maintained throughout the wholecourse of the fermentation, even if we omit the precaution of 352 STUDIES ON FERMENTATION. increasing the power of the syphon by making the tube forthe escape of this gas longer than the other one.* It will be readily understood how, whether by this lastmethod, or by the diameter of the tubes, we may vary the. Fig. 80. conditions of this circulation of air in the apparatus, on thesurface of the beer. * We may here remark that the system of gutters in the aboveapparatus is much simpler than that described in connection with and 77. The water which falls on the cover is carried oflF, when thegutter is full, by a circle of grooves, inclined so that the streams runningfrom them meet and form more readily a sheet of water, which flows overthe exterior surface of the cvlindrical vessel. STUDIES ON FERMENTATION. 353 S^ II.—Method of Estimating the Oxygen held in Solution IN Wort. The use of carbonic acid gas and the cooling of the wort,in contact with that gas or in contact with very limited quan-tities of pure air, are by no means necessary to the applicationof the new process. There is only one thing that is absolutelyessential—which is, the purity of the gases in the presenceof which the
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