Jellett — On Optical Saccharometry. 
167 
XXVII. — On Opticai, Sacchahometet, with special eefeeence to an 
Examination op some Specimens of Sugar Beet geown in Ieeland. 
By John H. Jellett, B. D., President. 
[Read May 22, 1871.] 
Befeeeinc to a paper read before the Academy some time ago by Dr. 
Apjohn, having for its object the determination of the amount of each 
of three kinds of sugar contained in a given syrup, the author said 
that his present object was to describe to the Academy the method of 
using for this purpose an instrument which he had formerly exhibited 
to them, and an account of which is published in the Proceedings" 
for 1863. 
The method is as follows. Three observations are necessary to be 
made with the optical instrument : — 
1 . The tube of the saccharometer being filled with the syrup to be 
examined, and the compensating fluid being French oil of turpentine, 
let the reading of the scale be li. 
2. The syrup having been subjected to the usual process for invert- 
ing the cane sugar, and the tube of the saccharometer being filled with 
the syrup so inverted, let the reading of the scale, corrected for the 
dilution of the syrup in the process of inversion, be ; the compensat- 
ing fluid being an aqueous solution of cane sugar, 100 grains to the 
cubic inch. 
3. The tube of the saccharometer is filled with the solution of cane 
sugar, used in (2), diluted with two parts of water. This dilution is 
necessary, inasmuch as the solution employed in (2) is too strong to be 
within the range of the instrument. Then, the compensating fluid 
being French oil of turpentine, as before, let the reading of the scale 
be Iz. Let I be the length of the tube of the saccharometer, and let 
€, i, g be the quantities of cane, inverted, and grape sugars respec- 
tively. Let also C, I, G be the rotatory power of these three sugars, 
and F the rotatory power of French oil of turpentine ; then we have 
from (1), 
I {Cc - li ■\- Gg) = Fly (1) 
from (2), 
I {{c-vi) I- Gg\ =100 Ck (2) 
and from (3), 
100 Cl=3Fl, (3) 
It is to be observed that all three sugars are reckoned throughout 
this investigation as if they had the same atomic weight as cane sugar, 
so that it will be necessary to augment the values found for the inverted 
and grape sugars in the ratio 171 : 198. 
