Union for butting two plastic bottles reused as teaching aid

摘要

A union is adapted to butt two reused plastic bottles at their mouths to provide a teaching aid for simulating the forming of spring and convection due to a pressure difference between two spaces. The union includes a hollow tubular body having a radially extended middle partition. An internal screw thread is provided on an inner wall surface of the union at each side of the middle partition to engage with an external screw thread on the mouth of the plastic bottle. The middle partition is provided with two symmetrical through holes, each of which is axially divided into two parts by a radially inward projected annular rib. Each part of the through holes is sized for a suction tube of predetermined dimensions to insert thereinto. By inserting two or three suction tubes into different parts of the two through holes, screwing the plastic bottles, one of which is partially filled with liquid, to two ends of the union, and turning the union upside down to locate the bottle having liquid at an upper position, the forming of springs and convections at different rates could be simulated in the bottles.