This essay will appear in our forthcoming book, “Making the Modern Laboratory,” to be published later this year.
In 1959, a pair of enterprising brothers, Jack and Harold Kraft, filed a patent titled “Apparatus for mixing fluent material.” Though simple in concept, their invention solved one of the most fundamental challenges faced by mid-century scientists: mixing fluids quickly and efficiently. The vortex mixer, a small motorized device that vibrated samples, offered the perfect solution, and is now found on biology benches across the world.
Harold and Jack Kraft were born in New York in the tumultuous years following World War I. From a young age, the boys displayed an entrepreneurial spirit and were always in business together. During the Great Depression, they made money by repairing broken radios and installing radio antennas on buildings in New York City. Family members recall Harold as the gregarious talker or salesman, while Jack led the technical side of their ventures.
Even World War II could not stop their abiding passion for motors and machines. Jack attended NYU School of Engineering while in the reserves, and Harold became an aircraft mechanic in the 519th Service Squadron, working at airfields in England and later France. After the war, the brothers reunited to take up business once again, this time manufacturing their own eponymous brand of Kraftone record players.
Jack Kraft, circa 1962. Credit: Scott Kraft
Harold Kraft, circa 1962. Credit: Scott Kraft
By the late 1950s, looking to break into scientific equipment, Jack reached out to fellow NYU alumnus and inventor, Dr. Samuel R. Natelson, a clinical chemist who was the Head of Biochemistry at St. Vincent’s Hospital of New York. Natelson kindly obliged Jack’s request, with the two meeting several times for chemistry demonstrations and discussions of the equipment challenges faced by Natelson and his colleagues.
During one such meeting, Natelson expressed a dire need for better mixing equipment. At the time, chemists had only a few options. If the solution volume was large enough, magnetic stir bars could be placed into the mixing vessel, but that meant they needed a corresponding electromagnetic stir plate upon which to place the solution. Most labs had only a few such plates, if any, so when making multiple solutions, there weren’t enough to go around. The alternative was to stir, shake, or flick the vessel manually. These apparatuses all needed cleaning between each use.
We may never know which specific mixture drew the ire of Natelson. But we can infer from a letter, drafted by the Kraft brothers, that it concerned viscous substances. The letter also reveals just how excited the brothers were about their invention. According to their account, Jack brought the original idea to Harold, and the two sketched out potential solutions on October 20, 1958. Just three days later, they had built their first prototype using the same kind of shaded pole AC motor found in their record players.
The resulting invention was simple, but elegant. A small, high-powered motor was housed within the body of a box-shaped machine. Mounted atop the motor was a rubber cup. Switched on, the motor oscillated the cup in tight orbital motions. When a test tube, or other vessel, touched the rubber cup, that motion transferred to the liquid, creating a vortex and mixing its contents.
... continue reading