In order to estimate the amount of carbon dioxide evolved in a given time and the total amount evolved by the action of yeast-juice on sugar, Buchner adopted an extremely simple method, which consisted in carrying out the fermentation in an Erlenmeyer flask provided with a small wash-bottle, which contained sulphuric acid and was closed by a Bunsen valve, and ascertaining the loss of weight during the experiment. Corrections are necessary for the carbon dioxide present in the original juice and retained in the liquid at the close of the experiment and for that present in the air space of the apparatus, but it was found that for most purposes these could be neglected. In cases in which greater accuracy was desired, the carbon dioxide was displaced by air before the weighings were made. A typical experiment of this kind, without displacement of carbon dioxide, is the following:-- March 22, 1899, Berlin bottom yeast V. 20 c.c. juice + 8 grams cane sugar + 0·2 c.c. toluene as antiseptic at 16°. Grams of carbon dioxide after 24 48 72 96 hours. 0·40 0·64 0·99 1·11 The total weight of carbon dioxide evolved under these conditions is termed the fermenting power of the juice (Buchner). A more accurate method [Macfadyen, Morris, and Rowland, 1900] consists in passing the carbon dioxide into caustic soda solution and estimating it by titration. The yeast-juice, sugar, and antiseptic are placed in an Erlenmeyer flask provided with a straight glass tube, through which air can be passed over the surface of the liquid, and a conducting tube leading into a second flask which contains 50 c.c. of 10 per cent. caustic soda solution and is connected with the air by a guard tube containing soda lime. The juice can be freed from carbon dioxide by agitation in a current of air before the flask is connected to [p028] that containing the caustic soda solution, and at the end of the period of incubation air is passed through the apparatus, the liquid being boiled out if great accuracy is required. The absorption flask is then disconnected and the amount of absorbed carbon dioxide estimated by titration. This is carried out by making up the contents of the flask to 200 c.c., taking out an aliquot portion, rendering this exactly neutral to phenophthalein by the addition first of normal and finally of decinormal acid, adding methyl orange and titrating with decinormal acid to exact neutrality. Each c.c. of decinormal acid used in this last titration represents 0·0044 gram of carbon dioxide in the quantity of solution titrated. [Illustration: FIG. 3. (Schiff's Azotometer--Ed.)]