THE FERMENT OF MADDEE ON SUGAR. 115 



tions proper to acetic acid. Whether the acetic acid thus 

 obtained is a product of the direct action of the ferment on 

 sugar, or whether it is formed indirectly from the oxidation of 

 the alcohol produced in the first instance, is uncertain. The 

 greater part of the acid found in the fermented liquor after 

 exposure for some time, in quantities so considerable as to 

 impart to the liquid a strong acid taste and smell, is without 

 doubt derived from the latter source. 



The last product of this process of fermentation which I 

 shall have to mention, is solid, and though the most interest- 

 ing of them all, is formed in such small quantities as to 

 render its identification difficult. In order to obtain an ap- 

 preciable quantity of it, it is necessary to employ several 

 pounds of sugar. The solution of sugar being mixed with 

 ferment and lime water in the proportions stated above, the 

 mixture is allowed to ferment, and to stand for several weeks 

 at least, after the disengagement of gas has ceased. The 

 liquid is then strained through calico, and the ferment which 

 remains on the calico in an apparently unchanged state, is 

 washed with water until the percolating liquid is no longer 

 acid. The liquid is then rendered alkaline by means of lime 

 water, and again strained, in order to separate a small quan- 

 tity of flocks thrown down by the lime. Sugar of lead is 

 now added to it, which produces a dirty pinkish-white pre- 

 cipitate. This is collected on a filter, washed with water, 

 and decomposed with sulphuretted hydrogen. The acid 

 liquid filtered from the sulphuret of lead is usually dark 

 brown or black, from sulphuret of lead in a state of suspen- 

 sion. During evaporation, however, it deposits this sul- 

 phuret of lead, and after being again filtered is clear, though 

 still very brown. After being evaporated almost to a syrup, 

 milk of lime is added to it, and the mixture is boiled. The 

 lime removes a quantity of phosphoric acid, which is probably 

 derived from undecomposed phoi^phates contained in the fer- 

 ment, and also a great part of the brown colouring matter. 



