Features: 1.This instrument is used for high school science class to explain atmospheric pressure. 2.This product consists of two cast iron hemispheres with pull rings. The two hemispheres are combined with each other to form a sealed container. One of the hemispheres has a gas guide valve. The air in the sealed hemisphere can be withdrawn through the valve. 3.The pressure difference between the sealing ball and the outside atmosphere compresses the two hemispheres, so that they cannot be separated within a certain pulling force. 4.Paint spraying surface, smooth and burr-free. 5.Metal ball is inside coated with rust preventing paint. specification:Item Type: Magdeburg Hemispheres Material: Cast Iron Color: Black Instructions: Wipe the contact surfaces of the two hemispheres, apply them with grease such as petrolatum, and rotate the two hemispheres relatively, then press firmly. Open the air guide valve, pump it with the pumping device, and after the gas is exhausted, close the valve. The instrument pull ring can hang a weight or pulled by the student, and the two hemispheres cannot be separated. Open the valve to make the air enters the ball. At this time, the air pressure is balanced inside and outside, and the two hemispheres are immediately separated. Maintenance & Repair: Do not hit or drop the instrument to prevent the hemisphere from being broken causing the seal is not good. Do not come into contact with corrosive objects and gases. PackageList:1 x Magdeburg Hemispheres with Pull Ring1 x Petrolatum