The negaton hydrocoil was a piece of nanotechnology equipment that natives of Arret used to construct androids.
In 2268, Thalassa asked Commander Scott to prepare them, utlizing drawings from Sargon as a reference. Although the chief engineer complied, he had his doubts that a device resembling a drop of jelly could be effective, suggesting they use microgears and a pulley instead. Thalassa felt Scott's suggestion to be inefficient in comparison. (TOS: "Return to Tomorrow")