Active powders can also be obtained by precipitating yeast-juice with alcohol, alcohol and ether, or acetone. The preparation is best effected by bringing the juice into 10 volumes of acetone, centrifuging at once and as rapidly as possible, washing, first with acetone and then with ether, and finally drying over sulphuric acid. The white powder thus obtained is not completely soluble in water but is almost entirely dissolved by aqueous glycerol (2·5 to 20 per cent.), forming a solution which has practically the same fermenting power as the original juice. The precipitation can be repeated without any serious loss of fermenting power. Prolonged contact of the precipitate with the supernatant liquid, especially when alcohol or alcohol and ether are used, causes a rapid loss of the characteristic property [Albert and Buchner, 1900, 1, 2; Buchner, E. and H., and Hahn, 1903, pp. 228-246; Buchner and Duchaček, 1909]. Dry preparations capable of fermenting sugar can also be readily obtained from yeast without any preliminary rupture of the cells. Heat alone (yielding a product known as hefanol) or treatment with dehydrating agents may be used for this purpose, and a brief allusion has already been made (p. 21) to the different varieties of permanent yeast (Dauerhefe) obtainable in these ways. The most important of these products are the dried Munich yeast (Lebedeff, see p. 25), and the material known as zymin, which is now made under patent rights for medicinal purposes by Schroder of Munich. The latter has proved of value in the investigation of the production of zymase in the yeast cell [Buchner and Spitta, 1902], and of many other problems concerned with alcoholic fermentation. In order to prepare it 500 grams of finely divided pressed brewer's yeast, containing about 70 per cent. of water, are brought into 3 litres of acetone, stirred for ten minutes, and filtered and drained at the pump. The mass is then well mixed with 1 litre of acetone for two minutes and again filtered and drained. The residue is roughly powdered, well kneaded with 250 c.c. of ether for three minutes, filtered, drained, and spread on filter paper or porous plates. After standing for an hour in the air it is dried at 45° for twenty-four hours. About 150 grams of an almost white powder containing only 5·5 to 6·5 per cent. of water are obtained. This is quite incapable of growth or reproduction but produces a very considerable amount of alcoholic fermentation, far greater indeed than a corresponding [p039] quantity of yeast-juice. Two grams of the powder corresponding to 6 grams of yeast and about 3·5 to 4 c.c. of yeast-juice, are capable of fermenting about 2 grams of sugar, whereas the 4 c.c. of yeast-juice would on the average only ferment from one-quarter to one-sixth of this amount of sugar. The rate produced by this amount of zymin is about one-eighth of that given by the corresponding amount of living yeast [Albert, 1900; Albert, Buchner, and Rapp, 1902].