THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[April 1,1871. 
794 
IpMimimtp nf Scientific Srariics. 
CHEMICAL SOCIETY. 
At the Meeting of this Society on March 2, a paper was 
read on “ The Distillation and Boiling-point of Glyce¬ 
rine,’ ’ "by Mr. Thomas Bolus. 
It is well known that when glycerine, subjected to the 
ordinary atmospheric pressure, is heated so much as to 
cause ebullition, it is more or less rapidly decomposed 
hy repeated distillations. This decomposition may be, 
however, entirely prevented by a reduction of the pressure 
in the apparatus employed to 12-50 mm. The boiling- 
point of glycerine was determined by effecting the dis¬ 
tillation in a long-necked flask, having a supplementary 
neck attached at right angles to the principal one. In 
the principal neck, the thermometer was fixed by the aid 
of a caoutchouc cork, while the smaller neck was con¬ 
nected in a similar manner with a two-necked receiver. 
The glycerine, together with a few fragments of tobacco- 
pipe (this latter being required to prevent the bumping 
which would otherwise occur), being placed in the retort- 
flask, the receiver was connected with a Sprcngel’s mer¬ 
curial pump and a manometer, the caoutchouc joints 
being made air-tight with glycerine in the usual way. 
Unless the glycerine distilled had been dehydrated by 
previous distillation in a vacuum, the first portion of the 
distillate consisted principally of water; afterwards, 
when the glycerine in a pure state came over, the tem¬ 
perature indicated by the thermometer was 179'5° C. 
At (this time the pressure on the liquid was 12*5 mm., a 
pressure nearly corresponding to the tension of aqueous 
vapour - at the temperature of the receiver. A deter¬ 
mination of the carbon and hydrogen in the glycerine 
distilled as above was made; the oxidant employed being- 
copper oxide, followed by oxygen gas (I.), 0-4281 grm. 
COo and 0-3439 grm. H 2 0. 
Theory. 
Found. 
✓- 
*--^ 
I. 
c s . . . 
. . 36 
39-1 
38-9 
Hg . 
. . 8 
8-7 
8-9 
Og . . 
. . 48 
52-2 
92 
100-0 
Under a pressure of 50 mm., glycerine distils without 
change at about 210° C. Glycerine, dehydrated by dis¬ 
tillation, absorbs water from the atmosphere to the ex- 
dent of about 50 per cent, of its weight. The amount 
absorbed is, as might he expected, very variable. 
On March 16, Mr. C. Houghton Gill read some notes 
■“ On the Examination of Glucose-containing Sugars.” 
Those engaged in the examination of low sugars and 
molasses have frequently had to complain of obtaining 
quite unintelligible results. It is well known that the 
solution of the sugary body is decolorized and clarified 
by the addition of basic lead acetate befoi-e submitting 
it to optical examination; hut Mr. Gill finds that the 
power of invert sugar to rotate a ray of polarized light 
is so greatly altered by the presence of this reagent, that 
the results obtained by the so-called polarization of 
syrups containing much invert sugar are worthless when 
the clarification has been effected in the ordinary way. 
The alteration of rotatory power of pure invert sugar by 
basic lead acetate is shown by the following experi¬ 
ments :— 
15 c.c. of a solution of invert sugar made up to 50 c.c. 
by water, observed with a Soliel’s saccharometer* in 
tube of 20, read - 28-25 at 24° C. 
15 c.c. of a solution of invert sugar with water and 2 c.c. 
of saturated solution of basic lead acetate, observed 
with a Sohel’s saccharometer in tube of 20, read 
- 24-7 at 24° C. 
The readings of this instrument x -—— = angular de* 
grees. 100 
15 c.c. of a solution of basic acetate solution alone, ob¬ 
served with a Soliel’s saccharometer in tube of 20, 
read + 57 at 25° C. 
These results have been confirmed by many other 
observations. 
The alteration producing this reversal of rotatory 
power takes place only on the levulose of the liquid; the 
dextrose suffers no change of optical properties. 
A solution of pure dextrose prepared from invert sugar, 
and reading 60-3, made up to 2 vols. by strong solu¬ 
tion of basic lead acetate, read 30-5. 
A solution of nearly pure levulose prepared by Dubrun- 
faut’s method, and reading —44 at 20° C., made up 
to 2 vols. by solution of basic lead acetate, read fl- 6 
at 20° C. 
The alteration of the rotatory power of levulose is not 
permanent. On removal of the lead, or on acidifying 
the liquid, the original rotatory power is restorod. The 
alteration is not due to the alkalinity of the lead solution 
as regards alkalinity alone, for weak soda or ammonia 
produce no such change till they begin to decompose and 
destroy the sugar. It is probable that a soluble lead 
compound of levulose possessed of dextro-rotatory power 
is formed. 
Now, when a sugar solution containing invert sugar is 
clarified by basic lead acetate, the invert sugar loses, in 
part or in whole, its levo-rotatory power, and the first 
direct reading is too high. When the liquid is acidified 
and inverted by heat, the original invert sugar has its 
true levo-rotatory power restored and added to that of 
the invert sugar proceeding from the cane-sugar, thus 
producing a greater “ difference” in the readings than 
that due to the cane-sugar alone, and consequently lead¬ 
ing to too high a result. 
The remedy for this difficulty is to remove the lead and 
acidify the liquid before making the first reading. For 
this purpose Mr. Gill uses a strong solution of sulphuric 
dioxide, which possesses the advantages of removing the 
lead and bleaching the liquid at the same time, while it 
is incapable of inverting cane-sugar in the cold even in 
twenty-four hours. The decolorizing effect is so great 
that even the worst treacles give liquids of a pale straw 
colour when thus treated, and, moreover, “ inversion ” 
can afterwards be performed without any fear of spoiling 
the colour, whereas by the ordinary method the liquid 
frequently becomes too red to allow of optical examina¬ 
tion. 
Another error also arises from the use of the lead-salt 
as a clarifier for those sugar solutions in which glucose 
is to he estimated by the use of Fehling’s copper solu¬ 
tion. The presence of lead here leads to a result much 
too low, since it also becomes partly reduced, and thereby 
necessitates the use of a greater volume of the saccha¬ 
rine solution which is called on to reduce lead as well as 
the known amount of copper. Sulphuric dioxide serves 
to remove the load, while excess of the reagent exerts no 
other action on the copper solution than that of facilita¬ 
ting the subsidence of the cuprous oxide. 
As illustrating the extent of the error which may he 
introduced by the presence of lead, tho following experi¬ 
ment, selected from many others, may be taken (solu¬ 
tions of invert sugar of the same strength used in each 
case):— 
Volume required to precipitate cuprous oxide from 10 
c.c. of Fehling’s liquid— 
(19 Free from foreign bodies, 10 c.c. 
(2.) Containing 10 per cent, of its volume of solution of 
basic lead acetate, 17 c.c. 
PHILADELPHIA COLLEGE OF PHARMACY. 
At the Meeting held January 17th, Dr. Pile continued 
his problems on alcoholic menstrua, for ascertaining 
the strength of and preparing alcohols of different per¬ 
centage from a definite strength alcohol. 
1. To reduce alcohol to any desired strength. 
