A New Grain Hardness Tester

.\ hardness tester, especially adapted for grain, was cor~structecl by modifying a commercial portable soft metal tester known as the Barcol Impressor. h preloaded stylus is forced into grain sections preparetl by rneans ot a microtome. The displacement of the stylus, nleasured by a dial micrometer, is used as a hardness index. This has been related to tlie l'ickers tlianlontl pyramid hardness which is a standard metallurgical test. A number of hardness lneasnrements may be made on a single transverse kcl-nel section. The tester may be used for a11 wheat varieties. Significant variations in hardness within a single wheat kernel section ha\e been den1onstl.atetl. While the hardness of a block of lead varied over 5% hardness lumber, a kernel section of hard winter (Ponca) wheat exhibited hardness numbers ranging from 25 to 40, on the arbitrary scale of this testel-. Such terms as hnl-d~less and vitreousnes.~ have long been used to describe properties of grain of interest to wheat breeders and millers. Kiting or cutting grain has provided a qualitative evaluatiori ol' this property. A number of attempts have been niade to find a qu;irltitative rrleasure of the hardness of individual kernels or of the average hartlness of a collection of kernels. The Snletar hardness tester, produced by Rliag, utilizes the penetration of a dianlond-shaped stylus into a section of a kernel as a rneasure of hardness (4). The impression in the endosperm is n~easured with a microscope. This apparatus is similar in conception to the Vickers hardness tester used in metallurgy, except that the stylus or the Sirietar tester is larger. Tha t is necessary, for the impression made in a wheat kernel section by a Vickers tester is diffcult to rneasure with the rnicroscope attached to the Vickers machine. As a result of the size of its stylus, essentially only one or two measurements can 1)e made on a wheat kernel section with the Smetar tester. A traditional method for measuring the hardness of hulk samples Manuscript received October 27, 1958. Contribution No. 69, I l r p a r t m ~ ~ n t of I'h\sics. Kansas Agricultural Experiment Station, Manhattan. 2 Department of Physics. 3 Department of Industrial Engineering. 394 GRAIN HARDNESS TESTER Vol. 36 is the laboratory-scale barley pearler (2). T h e fraction of a small sample of wheat which is pearled off in a short interval by an abrasive stone is used as a hardness index. Another index of hardness which has been used is the energy required to mill 1 g. of grain. The Brabender hardness tester, which consists essentially of a small burr mill fitted to the dynamometer coupling of the Farinograph, has been used by Paukner (3). Basically this device measures the torque required to drive the burr mill as a small sample of grain is milled. The data are then reduced to terms of the energy required per milled gram of grain. I n the present work, the penetration of a small spring-loaded stylusinto a kernel section is used as the basis of hardness measurement. A commercial portable hardness tester called the Barcol Impressor (manufactured by the Barber-Colman Co., Rockford, Illinois) has been adapted for work with grain by suitable choice of the stylus tip and of the spring loading. I t has been possible to produce one model of the tester which is capable of 30 or more independent hardness measurements on a single wheat kernel section of hard wheat varieties. By increasing the radius of the stylus tip a second, more versatile model of the tester has been developed which is applicable to all wheat varieties under a wide range of ambient humidity. Approximately six independent measurements of the hardness of a single transverse kernel section may be made. Conversion of the Barcol Impressor into a Hardness Tester Suitable for Testing Wheat Sections The Barcol Impressor is a portable hardness tester designed for testing soft metals. The tester consists essentially of a spring-loaded stylus, a case, and a dial micrometer. Hardness is measured by the distance the stylus is displaced into the case when the tester is pressed against a test object. T h e greater the displacement of the stylus, the harder the object. Readings of the micrometer are referred to as hardness numbers. Adjustments are provided for setting the initial compression of the spring, and for setting the reading of the micrometer at its greatest deflection. The dial micrometer provided with the instrument has 100 divisions. For work with wheat, several modifications of the Impressor were necessary. T o provide a means of mounting and positioning a wheat kernel, the Impressor and a two-way microscope stage were mouqtetl on an oak platform. Kernel sections, cemented to microscope slides, could then be set into place and located to 0.1 mm. by the Vernier scale of the microscope stage. A photograph of the modified Impressor