370 T}ie Philosophical Society of Glasgow. 



The action of ferments, so far as these are concerned in the process 

 of sugar refining, next claims oui' attention. This is a subject which 

 presents many points of difficulty, yet it is too important to be wholly 

 omitted in such a discourse as the present. If sugar-canes are cut 

 during the rainy season, and allowed to lie over for a few days before 

 the juice is expressed, no crystallized sugar can be obtained from them — 

 only molasses, and even these of an inferior description. Again, if the 

 char-washings of the refinery are permitted to stand aside for a similar 

 period of time before they are boiled down, the sugar which they con- 

 tain is almost entirely destroyed. Occasionall}' the whole of the 

 syrups in a sugar-house undergo a peculiar kind of fermentation, con- 

 verting the syrups into a viscid condition, in which they refuse to 

 drain away from the crystallized sugar. This condition is known 

 technically as "smear,'' and its entrance into a sugar-house is consi- 

 dered analogous to the advent of a plague into a city, or of glanders 

 into an extensive stable. I have devoted considerable time to the study 

 of this highly obscure subject, and I think I have at last succeeded in 

 assigning a cause of which this smear is the probable result. 



It is well known that sugai* is liable to a variety of kinds of fermen- 

 tation, depending upon the presence of certain substances in a state of 

 change, the strength of the solution, its temperatm-e, and other causes. 

 Thus, when the solution is rather weak, and vegetable fibrine is present 

 (as in grape juice), the yeast plant, the sporules of which are constantly 

 floating in the atmosphere, readily vegetates, and the result is the 

 breaking up of the sugar into alcohol and carbonic acid. Again, when 

 the liquid contains caseine, as in milk, and the liquid is in a condition 

 favourable to the putrefactive decomposition of this nitrogenous prin- 

 ciple, the sugar is converted into lactic acid. When the tempera- 

 ture is high (90° to 110°), on the other hand, and some nitrogenous 

 matter is also present, the sugar undergoes the viscous fermentation, in 

 which a mucilaginous matter, mannite, and other substances, are formed. 

 The viscous fermentation occurs with peculiar rapidity in the expressed 

 juice of the beet and many other vegetables ; and in the manufacture of 

 rum m the West Indies it has to be kept in check by the addition 

 of sulphuric acid. In the sugar-house we have many of the conditions 

 fulfilled which are necessary for the development of the viscous fermen- 

 tation, and although the mucilaginous matter is never formed in such 

 quantity as to separate from the Hquid, yet I have no doubt that this, 

 or some other aUied body with which we ai-e yet unacquainted, is the 

 cause of syrups becoming smeary. It occurred to me that the spread 

 of this fermentation through the different floors of a sugar-house, from 

 mould to mould, until all assumed the same aspect, might be connected 



