106 
PHARMACY AT THE DUBLIN EXHIBITION. 
Saccharometer, invented by the Rev. John H. Jellett, M.A., J.’l.C.D. Apart 
from the fact that this instrument is a very great improvement upon that of 
Soleil, and is capable of solving problems with which the latter apparatus has 
not sufficient delicacy to cope, a short description of it will be rendered more 
interesting when I say that it is likely to become to the analytical chemist an 
ally of at "least as great value as the spectroscope. 
In the Proceedings of the Royal Irish Academy, vol. vii. p. 348, Professor 
Jellett described a new form of analysing prism , which it afterwards occurred 
to him could be applied to the construction of a saccharometer. The instru¬ 
ment of Soleil is, according to Professor Jellett, incapable of great accuracy ; 
the error to which even an accurate observer is liable in using it being not less, 
in the case of a saccharine solution, than half a grain per cubic inch. 
The new apparatus consists of, firstly, a means of obtaining a parallel beam 
of light; next, a Ricol’s prism, by which this beam is polarized. The polarized 
beam passes through a tube containing a fluid, having a rotative power opposite 
to that of the fluid under examination. This latter fluid is contained in a 
narrow tube, the ends of which are closed by plates of parallel glass, and this 
tube has a motion along a graduated bar, and can be made to enter the larger 
tube containing the turpentine or other compensating fluid to any required 
depth. As the zero of the scale is made to coincide with the point at which the 
narrow tube dips in the compensatory fluid to the furthest extent possible, it is 
plain that the reading of the scale will indicate exactly the length of the column 
of fluid interposed. The analysing prism and an observing lens complete the 
instrument. 
Row, bearing in mind that the principle of this saccharometer is the compa¬ 
rison of the degree of rotation of a fluid whose rotative power is unknown with 
that of one in which it is known, we will suppose that we are about to ascertain 
the strength of a given solution of cane-sugar. In this case French oil of tur¬ 
pentine will be the compensating fluid, and the vessel before described is filled 
with it. The tube is then filled with a sugar solution of known strength , and 
the zero of the vernier made to coincide with the zero of the scale. The tube 
is now moved back by means of its attached milled head until the tints on the 
two halves of the circular spectrum, which is seen on looking through the analys¬ 
ing prism, become equal in intensity. The reading of the scale is then noted. 
Let this be called R, and let S be the strength of the known sugar solution. 
The sugar solution of known strength is now removed from the tube, and 
replaced by that of which the strength is required. The same process having 
been repeated, the scale is read, and the new reading called R\ Then the quan¬ 
tity of sugar contained in the unknown solution is obtained by the equation :— 
If the operation have been carefully conducted, the error should not, according 
to Professor Jellett, exceed 0’02 grain per cubic inch for a single experiment. 
Of course this error would be even still less, if the mean of a number of experi¬ 
ments be taken. 
Professor Jellett has called the instrument a saccharometer because it would 
be best recoguized under this name, but he more accurately defines it to be “ an 
instrument by which the ratio of the rotatory power of any transparent fluid to 
that of a standard fluid may be determined.” 
Professor Jellett is at present engaged in a series of researches on the alka¬ 
loids, which I have reason to believe will be, when published, of the highest 
value, as by his method many questions can be solved which chemistry is incom¬ 
petent to answer. My readers know already that the identity of the aconellcc 
of Messrs. Smith, of Edinburgh, with narcotine has been conclusively established 
by Professor Jellett. The adulteration of glycerine with sugar, the substitution 
