Use/History: The Abbé refractometer provides
a quick and easy means for determining refractive index and dispersion
of liquids and solids. It is used in the examination of organic
compounds (oils, solvents, etc.), solutions, food products, and
serum protein concentration. The instrument is operated by aligning
the cross hairs in the telescope with the line of total reflection.
This line is adjusted by rotating the prism assembly with the
alidade. The refractive index is then read off directly from
the graduated arc to four significant figures. Reading at constant
temperature is important, thus the prisms are enclosed in a water
jacket which may be connected to a constant temperature bath.
Ernst Abbé published his Neue Apparate....
(1874) in which he discussed the theory and described instruments
for the measurement of refractive index using prisms and by total
reflection.1 It is here that he first describes the
Abbé refractometer for determining the refractive index
of fluids. This initial instrument includes Amici prisms and
is essentially the same as a modern Abbé refractometer,
though without temperature jacketing. The Spencer Lens Company
began selling an Abbe refractometer in about 1922. It differed
from the current instrument in having a tripod base and a gear-drive
alidade. The base was redesigned by 1924. The current instrument
was in use at Humboldt from 1953 until it was replaced in 1982.
Early descriptions of the features and use of the Abbé
refractometer are provided below:
Description: The instrument stands 11.5" high
in the closed, vertical position. The base is of cast iron with
black crinkle finish, some of which has come off to expose the
iron below the mirror rail. The scale and readout arms are of
steel. All of the control knobs and the alidade handle are in
heavy chrome plating. The solid metal two sided mirror is mounted
on an adjustable dovetail slide. The scale is engraved on an
inlayed german silver strip with scale divisions to the thousands
place (nD 1,3001,710), and numbered to the hundreds place.
The number: 788432618 is engraved on the scale just past 1710.
The readout is viewed with an adjustable triplet magnifier. A
hairline engraved on a glass window affixed via a threaded retaining
ring to the prism alidade determines the index. The prism alidade
has a tangent screw fine adjustment. The refractometer telescope
is heavy black enameled brass, with the AO shield logo engraved
and white filled on the arm over Spencer and the serial number:
2009. The Amici color compensating prism scale is finished in
brushed chrome with black filled engraved divisions (0-60-0)
and adjusted with a knurled wheel. The prism holder is finished
in brushed chrome with polished chrome tubulatures for connecting
to a circulating bath for temperature control. There is a chromed
brass thermometer shield and mercury-filled thermometer. Engraved:
HSU 43923.
The instrument has its original black leatherette covered
hardwood case and its original glass block refractive index standard
in a small plastic vial (shown in the photo).
Research: This instrument is described in detail in
the 1953 (?) American Optical Company Scientific Instrument catalog
as item 10075, AO Spencer Standard Refractometer with Amici prisms.
It is also shown as item 73563 - Refractometer - Abbe, with
Amici Prisms on pg. 782 of the 1950 Adolf Frese Corp. Catalog.
According to HSU Inventory this instrument was purchased in 1953
for $556.20.
A detailed treatment of refractometry and refractometers
is given in: Tilton, Leroy W. and John K. Taylor. "Refractive
Index Measurement." in Physical Methods in Chemical Analysis
Vol. 1, 2nd ed. ; Walter G. Berl, editor (1961) pp41162.
References:1 Abbé, E. Neue Apparate
zur Bestimmung des Brechungs - und Zerstreuungsvermögens
fester und flüssiger Körper. Mauke's Verlag, Jena
(1874) Taffel: Fig. 5-7.
