The arrangement of the rooms in which polarizations are performed has
an important bearing upon the accuracy of the results obtained.
Polariscopic observations are made more readily and accurately if the
eye of the observer is screened from diffused light; therefore, a
partial darkening of the room, which may be accomplished by means of
curtains or hangings, is an advantage. On the other hand, the
temperature at which the observation is made has a very considerable
influence upon the results obtained, so that the arrangements for
darkening the room must not be such as will interfere with its proper
ventilation. Otherwise the heat from the lamps used, if confined
within a small room, will cause considerable variations in the
temperature of the room from time to time.
The proper conditions will best be met, in our opinion, by placing the
lamps either in a separate room from that in which the instruments
are, and perforating the wall or partition between the two rooms for
the light to reach the end of the instruments, or in a ventilated hood
with the walls perforated in a like manner. By lining the wall or
partition on both sides with asbestos paper, and inserting a plate of
plane glass in the aperture through which the light passes, the
increase of temperature from the radiation of the lamp will be still
further avoided. With the lamps separated from the instruments in this
manner, the space in which the instruments are contained is readily
darkened without much danger of its temperature being unduly raised.
Some light, of course, is necessary for reading the scales, and if
artificial light is employed for this purpose, the sources chosen
should be such that as little heat as possible will be generated by
them. Small incandescent electric lights are best for such purpose.
Refinements of this kind cannot always be used, of course, but the
prime requisite with reference to the avoidance of temperature errors
is that all operations--filling the flasks and tubes, reading the
solutions, controlling the instrument with standard quartz plates,
etc.--should be done at one and the same temperature, and that this
temperature be a constant one, that is, not varying greatly at
different hours of the day. For example, the room should not be
allowed to become cold at night, so that it is at low temperature in
the morning when work is begun, and then rapidly heated up during the
day. The polariscope should not be exposed to the direct rays of the
sun during part of the day, and should not be near artificial sources
of heat, such as steam boilers, furnaces, flues, etc.
The tables upon which the instruments stand should be level.