Comparing to an ordinary dropping funnel, the Pressure-equalizing dropping funnels have an additional narrow-bore glass tube from the upper part of the funnel bulb to the ground glass joint around the stem at bottom. With standard taper glass outer joint at Top and inner joint at bottom, with high vacuum valve .Laboy glass flasks are heavy wall designed, made by hand-blowing to ensure uniform wall thickness, made of high-quality borosilicate glass and annealed at 800 degree Celsius, can be heated directly in an open flame and can withstand typical laboratory thermal variations in Chemistry processes like heating and cooling.