Db. W. Wallace on the Chemistry of Sugar Refining. 3G7 



May 4, 1859. — The President in the Chair. 



Mr. James Henderson exhibited the British Sewing Machine lately 

 invented and patented by Mr. S. C. Blodgett. 



Professor Kankine read "A Provisional Classification of Machines 

 according to their purposes, with a view to the appointment of a Com- 

 mittee upon the several Classes." 



Dr. Wallace read a paper on Sugar refining. 



On some Points in the Chemistry of Sugar Refining. By William 



Wallace, Ph.D., F.C.S. 

 The manufacture of sugar is a strictly chemical process, although 

 involving, like many other processes which depend upon chemical prin- 

 ciples, many important mechanical details. There are, perhaps, few 

 manufactures of such importance as sugar refining, of which so little is 

 known by the general public ; and I trust, therefore, that a brief descrip- 

 tion of the process, together with an explanation of the scientific prin- 

 ciples involved, will not be unacceptable to the members of this Society. 

 The position of the trade as one of the industrial resources of the West 

 of Scotland will be appreciated, when it is stated that there are in Glas- 

 gow, Greenock, and Port-Glasgow, fifteen or sixteen houses which, 

 collectively, are computed to refine annually at least 75,000 tons of raw 

 sugar, worth about £3,000,000. Thei'e is one house in Glasgow, and 

 one or two in Greenock, which turn out each 200 tons a-week, or at 

 the rate of 100 pounds per minute. 



There are many varieties of sugar, of which the three most impor- 

 tant kinds are cane sugar or sucrose (Cjj Hj^ On), fruit sugar or fruc- 

 tose (Ci2 Hi2 O12), and grape sugar or glucose (Cjg H14 Oj^). The two 

 last varieties, indeed, are often confounded together, and many chemists 

 consider them identical ; but the generally received opinion now enter- 

 tained is, that there is no such thing as grape sugar produced by the 

 vital functions of plants, but that it is formed, under particular circum- 

 stances, from fruit sugar, by the assimilation of two equivalents of water. 

 Indeed, all the other sugars seem to change readily into glucose ; and 

 even starch and lignine, as is well known, are easily converted into 

 this substance by the action of acids. In all cases the change is owing 

 simply to the absorption of the elements of water. Very weak acids, 

 with the aid of heat, effect the conversion of cane sugar first into fruit 

 and then into grape sugar : an elevated temperature alone, in presence 

 of water, accomplishes the same transformations, but much more 

 tardily. The following experiments, made with a solution of pure sugar 

 in distilled water, will illustrate the danger of keeping syrups at an 



