108 



AGRICULTURAL CHEMISTRY. 



tne common frothy yeast can cause the kind 

 of fermentation by which the former kind 

 of yeast is produced. 



When common yeast is added to wort at 

 a temperature of be'tween 40 and 45 F., a 

 slow tranquil fermentation takes place, and 

 a matter is deposited on the bottom of the 

 vessel, which may be employed to excite 

 new fermentation ; and when the same ope- 

 ration is repeated several times in succession, 

 me ordinary fermentation changes into that 

 process by which only precipitated yeast is 

 formed. The yeast now deposited has lost 

 the property of exciting ordinary fermenta- 

 tion, but it produces the other process even 

 at a temperature of 50 F. 



In wort subjected to fermentation, at a 

 low temperature, with this kind of yeast, 

 the condition necessary for the transforma- 

 tion of the sugar is the presence of that 

 yeast ; but for the conversion of gluten into 

 ferment by a process of oxidation, some- 

 thing more is required. 



When the power of gluten to attract oxy- 

 gen is increased by contact with precipitated 

 yeast in a state of decay, the unrestrained 

 access of air is the only other condition 

 necessary for its own conversion into the 

 same state of decay, that is for its oxidation. 

 We have already seen that the presence of 

 free oxygen and gluten are conditions which 

 determine the eremacausis of alcohol and 

 jts conversion into acetic acid, but they are 

 incapable of exerting this influence at low 

 temperatures. A low temperature retards 

 the slow combustion of alcohol, while the 

 gluten combines spontaneously with the 

 oxygen of the air, just as sulphuric acid 

 does when dissolved in water. Alcohol un- 

 dergoes no such change at low temperatures, 

 but during the oxidation of the gluten in 

 contact with it, is placed in the same condi- 

 tion as the gluten itself when sulphurous 

 acid is added to the wine in which it is con- 

 tained. The oxygen of the air unites both 

 with the gluten and alcohol of wine not 

 treated with sulphurous acid ; but when this 

 acid is present it combines with neither of 

 them, being altogether absorbed by the acid. 

 The same thing happens in the peculiar pro- 

 cess of fermentation adopted in Bavaria. The 

 oxygen of the air unites only with the gluten 

 and not with the alcohol, although it would 

 have combined with both at higher tempe- 

 ratures, so as to form acetic acid. 



Thus, then, this remarkable process of 

 fermentation with the precipitation of a mu- 

 cous-like ferment consists of a simultaneous 

 putrefaction and decay in the same liquid. 

 The. sugar is in the state of putrefaction, 

 and the gluten in that of decay. 



Appert's method of preserving food, and 

 this kind of fermentation of beer, depend on 

 the same principle. 



In the fermentation of beer after this man- 

 ner, all the substances capable of decay are 

 separated from it by means of an unre- 

 strained access of air, while the temperature 

 is kept sufficiently low to prevent the alco- 



hol from combining with oxygen. The re 

 moval of these substances diminishes the 

 tendency of the beer to become acescent, or 

 in other words., to suffer a farther transforma 

 tion. 



In Appert's mode of preserving food, 

 oxygen is allowed to enter into combination 

 with the substance of the food, at a tempe- 

 rature at which decay, but neither putrefac 

 tion nor fermentation, can take place. With 

 the subsequent exclusion of the oxygen and 

 the completion of the decay, every cause 

 which could effect farther decomposition of 

 the food is removed. The conditions for 

 putrefaction are rendered insufficient in both 

 cases; in the one by the removal of the 

 substances susceptible of decay, in the other 

 by the exclusion of the oxygen which would 

 effect it. 



It has been stated to be uncertain, whether 

 gluten during its conversion into common 

 yeast, that is, into the insoluble state in 

 which it separates from fermenting liquids, 

 really combines directly with oxygen. If it 

 does combine with oxygen, then the difference 

 between gluten and ferment would be, that 

 the latter would contain a larger proportion 

 of oxygen. Now it is very difficult to as- 

 certain this, and even their analyses cannot 

 decide the question. Let us consider, for 

 example, the relations of alloxan and allox- 

 antin* to one another. Both of these bodies 

 contain the same elements as gluten, although 

 in different proportions. Now they are known 

 to be convertible into each other, by oxygen 

 being absorbed in the one case, and in the 

 other extracted. Both are composed of ab- 

 solutely the same elements, in equal pro- 

 portions ; with the single exception, that al- 

 loxantin contains 1 equivalent of hydrogen 

 more than alloxan. 



When alloxantin is treated with chlorine 

 and nitric acid, it is converted into alloxan, 

 into a body, therefore, which is alloxantin 

 minus 1 equivalent of hydrogen. If on the 

 other hand a stream of sulphuretted hydro- 

 gen is conducted through alloxan, sulphur 

 is precipitated, and alloxantin produced. It 

 may be said, that in the first case hydrogen 

 is abstracted, in the other added. But it 

 would be quite as simple an explanation, if 

 we considered them as oxides of the same 

 radical : the alloxan being regarded as a 

 combination of a body composed of C 8 N 

 H O with 2 equivalents of water, and al- 

 loxantin as a combination of 3 atoms of 

 water, with a compound consisting of C* 

 N H> O*. The conversion of alloxan into 

 alloxantin would in this case result from its 

 eight atoms of oxygen being reduced to 

 seven, while alloxan would be formed out 

 of alloxantin, by its combining with an ad- 

 ditional atom of oxygen. 



Now, oxides are known which combine 

 with water, and present the same pheno- 

 mena as alloxan and alloxantin. But no 



* Compounds obtained by the action of nitric 

 acid on uric acid. 



