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108 THE MICRO-ORGANISMS OF THE HUMAN MOUTH. ;
the water-bath. A portion of the sohition tested in the short
tube of a MitscherHch double-shadow polaristrobometer gave, as
a mean of nine readings, a rotation of the plane of polarization
equal to 0.015 degree, or 0° 0.9'. In other words, the solution
was optically inactive, the 0° 0.9' being far within the range of
the error of experiment, especially as the solution was not abso-
lutely transparent.
An excess of freshly prepared oxide of zinc was then added to
the solution, and the whole slowly and carefully boiled, water
being added as it was found ne-
cessary, till the reaction became
Fig. so.
neutral, or nearly so, filtered
into a large glass evaporating
dish, and put away at the tem-
perature of the room for the salt
to crystallize. A drop of this
solution placed upon a glass
slide gave, upon crystallization,
the forms seen in Fig. 52, which
are at once recognized as crys-
tals of lactate of zinc. In a few
days a quantity of a whitish
Crystals of L.\ctate of Zisc. crystalline powder had formed.
This was placed upon a filter,
the mother-liquid squeezed out, washed in absolute alcohol, dis-
solved in hot water, recrystallized and dried over sulphuric acid
it then weighed 0.343. After exposing to a temperature of 100°
C, or a little more, till the weight became constant, it weighed
0.2816; it lost accordingly 17.9 per cent.* of water of crystalli-
zation, corresponding to three molecules of water. The salt was
then dissolved in water, the zinc precipitated as carbonate and
burned. The burned mass (zinc oxide) weighed 0.0970. We
have, consequently,
Substance analyzed (a zinc salt) =: 0.343
Oxide of zinc = 0.097
The zinc oxide is seen to be equivalent to 28.2 per cent, of the
substance analyzed.
* Theoretically 18.2, or 0.3 per cent. more.
108 THE MICRO-ORGANISMS OF THE HUMAN MOUTH. ;
the water-bath. A portion of the sohition tested in the short
tube of a MitscherHch double-shadow polaristrobometer gave, as
a mean of nine readings, a rotation of the plane of polarization
equal to 0.015 degree, or 0° 0.9'. In other words, the solution
was optically inactive, the 0° 0.9' being far within the range of
the error of experiment, especially as the solution was not abso-
lutely transparent.
An excess of freshly prepared oxide of zinc was then added to
the solution, and the whole slowly and carefully boiled, water
being added as it was found ne-
cessary, till the reaction became
Fig. so.
neutral, or nearly so, filtered
into a large glass evaporating
dish, and put away at the tem-
perature of the room for the salt
to crystallize. A drop of this
solution placed upon a glass
slide gave, upon crystallization,
the forms seen in Fig. 52, which
are at once recognized as crys-
tals of lactate of zinc. In a few
days a quantity of a whitish
Crystals of L.\ctate of Zisc. crystalline powder had formed.
This was placed upon a filter,
the mother-liquid squeezed out, washed in absolute alcohol, dis-
solved in hot water, recrystallized and dried over sulphuric acid
it then weighed 0.343. After exposing to a temperature of 100°
C, or a little more, till the weight became constant, it weighed
0.2816; it lost accordingly 17.9 per cent.* of water of crystalli-
zation, corresponding to three molecules of water. The salt was
then dissolved in water, the zinc precipitated as carbonate and
burned. The burned mass (zinc oxide) weighed 0.0970. We
have, consequently,
Substance analyzed (a zinc salt) =: 0.343
Oxide of zinc = 0.097
The zinc oxide is seen to be equivalent to 28.2 per cent, of the
substance analyzed.
* Theoretically 18.2, or 0.3 per cent. more.
