Set the system so that the short achromatic' section of
(2) Liquids are measured by introducing a thin film
the borderline is centered on the crosshairs.
between the upper and lower refracting prisms. Solids
are measured by affixing them to the surface of the lower
prism by means of a suitable contact liquid which must
A snap-on plastic cover is provided
be higher in index than the sample to be measured.
to cover the compensator scale dial.
(3) The miniature-type field lamp is operated from
Use the cover to prevent the samples
from running inside the instrument.
the line switch. The internal scale lamp is operated by a
(9) The thermometer is attached in an upright
momentary contact switch on the side of the instrument.
position by means of two knurled collars.
Normally the field lamp is on while the internal scale
thermometer may be adjusted to any reading position by
lamp is off. Depressing the momentary contact switch
loosening the collars, adjusting the thermometer to the
lever reverses this condition.
desired position, and then tightening the collars.
(4) The upper prism is the illuminating prism, and
the lower prism is the measuring prism. When the
(1) Place the sample in position on the instrument
prisms are closed, a liquid sample may be introduced by
and set the scale at the approximate value expected. To
pipet or dropped through the channel between the prism
see the scale, depress the momentary contact switch on
boxes. The prism housings are hollow and provide for
the side of the instrument.
the flow of liquid to hold the prism at a constant
(2) Release the contact switch and bring the
borderline, which will probably be strong colored, near
(5) A small hinged shield on the lower prism
the crosshair. Compensate the color by adjusting the
housing blocks off the front face of the refractometer
position of the dial. The borderline should be faintly blue
prism to prevent the entrance of stray light. When
on one side and faintly red on the other side.
reflected light is required to enter the front face of the
(3) Observe the crosshairs, sharply focusing the
refraction prism, the shield is rotated out and down
eyepiece if necessary, and bring the dividing line upon
toward the base of the instrument. The polished surface
their intersection by means of the coarse or fine hand
of the shield may be used as a reflector to provide
(4) Read the index by depressing the momentary
(6) The index and total solids are photographed on
contact switch, estimating the fourth place.
a transparent glass plate which is attached to the sector
(5) If working with liquids, record both index and
arm inside the housing. The scales are read through the
prism temperature at the time of reading.
eyepiece by depressing the momentary contact switch.
Follow the test procedures of ASTM Methods D1218 (TM
Focus the eyepiece for best results.
10-1167) and FTMS 791, Method 5340.
(7) A mirror is used to direct the total reflection line
from the refracting prism into the viewing system. It is
The refractometer should be kept in
mounted on a pivoted ball bearing sector. Its position,
the case when not in use to prevent
calibrated in index or percent solids, is indicated on the
the accumulation of dust and grit.
scales attached to the sector, which is moved by turning
the concentric handwheels on the side of the instrument.
a. Description. The penetrometer (fig.
The larger of the two wheels is a fast friction disk drive
designed to comply with the requirements specified in
traversing the entire index range in two and a quarter
ASTM Method 217 (TM 10-1166). It is stored in cabinet
turns. The smaller wheel is a slow planetary ball bearing
K3 (figs. 1-2, 2-30 and B-16). The penetrometer is used
drive requiring 11 turns to traverse the range. Any slight
to measure penetration of grease with a penetration
backlash which may exist will not affect the accuracy of
cone. The penetration includes a dial for measuring
depth of penetration up to 38 millimeters on a single
(8) The compensator unit and both prisms move
sweep of the dial needle. The unit is provided with
together in the same direction. The scale dial serves to
stainless steel plunger bearings, preliminary setting and
rotate them. When correct compensation has been
fine pitch micrometer adjustments, clutch, ASTM 2.5
secured, the borderline will be achromatic at the center
gram needle, and a 50 gram weight.
of the field with a faint red dispersion showing at one
extremity and a faint blue dispersion showing at the other