THE 
PROCEEDINGS 
OF 
ROYAL IRISH ACADEMY. 
SCIENCE. 
PAPERS READ BEEORE THE ACADEMY. 
I. — On a neav Step iisr the Proximate Aj^^alysis of Sacchaeine 
Matters. By James Apjohn^, M. D., F. R. S. 
[Read November 30, 1869.] 
COMMERCIAL sugars and syrups (he stated) usually consist of cane 
sugar, intermixed with, variable proportions of two other varieties 
of saccharine matters — namely, crystallized glucose, or grape sugar, and 
inverted sugar ; but the value of a crude sugar or a syrup chiefly depends 
upon the amount of cane sugar present in it, and hence mucji interest 
has always attached to the methods adopted for determining its 
amount. The percentage of cane sugar in a syruj), containing no 
other active substance, admits, as is well known, of being determined 
by the rotation which it exerts upon the plane of polarization of a ray 
of plain polarized light ; and though the two other sugars should be 
present, one of which (the grape sugar) rotates to the right, while the 
other rotates to the left, there are means of determining the rota- 
tion due to the cane sugar, from which its amount may be calculated. 
As respects, however, the inverted and grape sugars, the quantities of 
these present cannot be determined solely by optical means ; and the 
principal object of his Paper, Dr. Apjohn observed, was to explain 
how the complete proximate analysis of a syrup including the three 
sugars could be made. 
His method of accomplishing this object he then showed to consist 
in the performance of two optical experiments — one before, and the 
other after the inversion of the syrup ; and a single chemical experi- 
ment, in which Ban^eswiir swell-known solution of copper is employed. 
R.I. A. PROO. — VOL. I., SER. II., SCIEXCE. B 
