Humboldt State University
Robert A. Paselk Scientific Instrument Museum
This is a so-called Canner's Refractometer. It is designed for the canning and food industries, having a percent solids scale for reading the concentrations of sugar solutions directly. The percent solids scale is engraved next to the standard 1.3 - 1.7 refractive index scale divided to the third decimal with estimation to the fourth. It also has a simplified Amici prism adjustment with restricted rotation and no graduations. In other respects it corresponds to the Precision Refractometer from Valentine. The instrument is very solids and smooth in operation.
According to the Franklin Institute article1 describing this instrument, it was designed by Warren Valentine after a study of the Zeiss Abbe refractometer in 1917. However, the lack of available mechanics capable of the precision work and lack of optics, due to the war effort, prevented completion of the first instrument until 1919. This study and replication effort resulted in Valentine constructing a second instrument with improvements to both mechanical and optical components to provide greater stability and accuracy than the traditional Abbe design. The 1928 article describes both the "fourth decimal" Precision Refractometer and the "fifth decimal" Improved Precision Refractometer.
The Abbe refractometer provides a quick and easy means for determining refractive index and dispersion of liquids and solids. Its most common use is the determination of the concentrations of solutions. A brief essay, The Chemical Refractometer, describes the characteristics, design, and use of these instruments. A detailed history, The Evolution of the Abbe Refractometer, traces the development of this valuable instrument to around 1980.
The instrument stands 12 3/8" high in the closed, vertical position. The 5 3/4" diameter by 1/2" high round base is a hollow casting. The entire instrument is made of heavy cast and fabricated brass. The counter-weighted sector arm and telescope mounts are finished in crinkle enamel, while the remainder of the instrument is black japanned. Exposed metal parts are finished in polished or brushed chrome plate. The instrument is stamped with white filling on the main bearing cap: VALENTINE REFRACTOMETER / No 1119 / INDUSTRO-SCIENTIFIC CO. The instrument has a 0-100% total solids scale engraved next to the standard (n = 1.3 - 1.7) refractive index scale.
The instrument has its original mahogany case (13 3/4"h x 7 1/4"w x 7 3/4"d) with two brass hook latches. The leather handle is a replacement. The thermometer and other accessories are missing.
1 Valentine, W. P. (1929) J. Franklin Inst. 207, 116.