SPECIFIC GRAVITY
��certain radicals (OH, CH 3 , &c), we generally find that the volatility of the substances is favoured by the two following circumstances :
(a) by the central position in the molecule of the sub- stituting atom or radical.
Examples. —
( (CH^.CH.CHrCH^OH) boiling point 128° to 132° C*H 12 - (CH s ) 2 .CH.CH(OH).CH, „ „ 104° to 108°
��(CH^^CJOHJ.CHj.CH,
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�� ��98° to 102° (Naumann.) r j CHj.CH^CHCls . . boiling point 86<
(Henry), (ft) by the substituting atoms or radicals being close together.
Example. —
ICHjCLCH^CHjCl . . boiling point 119° CH..CHC1.CH2C1 . „ „ 96-8°
CH S .CH 2 .CHC1 2 . „ „ 86°
CH 8 .CC1 2 .CH S . „ 70°
(Henry).
This regularity applies also to the aromatic series (benzene-derivatives) where the di-substituted ortho- deri- vatives are generally more , volatile than the correspond- c ingpara- derivatives.
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��Specific Gravity
For information concern- ing areometers and pycno- meters the student is referred to text-books on physics. But here SprengeVs pycnometer may be mentioned. The ap- paratus can easily be made from ordinary glass-tubing (fig. 9). The reservoir b ends in two horizontal branches, one of which, c, is a fine capillary tube, whilst the other, b,
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