320 YEAST OR FERMENT. 



Putrefaction, on account of its effects, as a mixed 

 transformation of many different substances, may be 

 classed with the most powerful processes of deoxi- 

 dation, by which the strongest affinities are over- 

 come. 



When a solution of gypsum in water is mixed with 

 a decoction of sawdust, or any other organic matter 

 capable of putrefaction, and preserved in well-closed 

 vessels, it is found after some time, that the solution 

 contains no more sulphuric acid, but in its place car- 

 bonic and free hydrosulphuric acid, between which 

 the lime of the gypsum is shared. In stagnant water 

 containing sulphates in solution, cry&tallized pyrites 

 is observed to form on the decaying roots. 



Now we know, that in the putrefaction of wood 

 under water, when air therefore is excluded, a part 

 of its carbon combines with the oxygen of the water, 

 as well as with the oxygen which the wood itself 

 contains ; whilst its hydrogen and that of the de- 

 composed water are liberated either in a pure state, 

 or as carburetted hydrogen. The products of this 

 decomposition are of the same kind as those genera- 

 ted when steam is conducted over red-hot charcoal. 



It is evident, that if with the water a substance 

 containing a large quantity of oxygen, such as sul- 

 phuric acid, be also present, the matters in the state 

 of putrefaction will make use of the oxygen of that 

 substance as well as that of the water, in order to 

 form carbonic acid ; and the sulphur and hydrogen 

 being set free will combine whilst in the nascent 

 state, producing hydrosulphuric acid, which will be 

 again decomposed if metallic oxides be present ; and 

 the results of this second decomposition will be water 

 and metallic sulphurets. 



The putrefied leaves of woad (^Isatis tinctoria), in 

 contact with indigo-blue, water, and alkalies, suffer 

 further decomposition, and the indigo is deoxidized 

 and dissolved. 



The mannite formed by the putrefaction of beet- 

 roots and other plants which contain sugar, contains 



