These thistle tubes or long stem funnels are made of borosilicate (heat resistant) glass. The approximate dimensions are: top diameter 47mm, outer stem diameter 5mm and length 250mm (9.8 inches). This funnel is used for the direct introduction through a stopper of substances into a flask, not for filtration. The stem is normally below the surface of a solution such as is done in the generation of a gas by water displacement in a pnuematic trough. This tube can be used in osmosis demonstrations in conjunction with permeable membranes.