OPTICAL ROTATION

and, in general

This is usually written:

,,_._ -__

1.420(5 - 0.005 t

tr ___
A —

100(7' - /)
142.00 - 0.5*

133

(3)
(4)

t indicating temperature in degrees Centigrade.
Recent work1 at the Bureau of Standards has shown that the,
(Uerget divisor should be, 143.25 instead of 142.00, in presence
of the acid used to cause inversion.
The method is applicable only to materials containing no other
compounds whoso activity is changed by treatment with acids.
Molasses from boots and, to somes extent, beet sugar contain
certain quantities of ruffinoso (O^II.-^)^), a sugar whoso specific
rotation is +104.5°. This rotation is diminished by one-half by
warming with dilute acids. (See page 130.)
Commercial syrups of various kinds usually possess a color
which interferes with transmission of light and makes poluri-
scopie readings difficult. This color is due to a variety of
colored organic substances and to caramel formed during the
heating processes. It can be removed in most cases by addition
of a basic load salt, of which basic load acetate is most suitable,
or of "alumina cream," a suspension of colloidal aluminium
hydroxide in water, freshly prepared. In the case of load salts
the action is partly chemical and partly physical. Complex
lead salts of organic acids are formed and these, being colloidal
in character, flocculate and carry with them other colloidal
colored compounds. Neutral lead acetate is used in some* cases
where a basic reaction is to be avoided.
Correction for Volume of Precipitate.-—In the method an
usually followed the clarified solution is diluted to 100 ee before
filtration. This ignores the volume of the precipitate and an
error is introduced from this source. However, the actual vol-
ume occupied by this precipitate is much lens than the apparent
volume, owing to its colloidal nature. If there is produced a
larger quantity of precipitate than can safely bo ignored the
double dilution method of correction is used. In this method
one polarization is made on the clarified solution which has boon
»U. S. Bur, Stand. Bd. Paper, 375 (1920).