Water 28 APPLICATION OF THE LAWS OF HYDRAULICS Assume that a bell glass with an orifice of an area w, within which the kerosene is con- stantly maintained at a height PI (Fig. 22), is im- mersed in water. Neglect- ing, for the moment, the coefficients of contraction /q and of velocity /C2, which, for this case, have not been de- termined, the formula for the flow will be simplified. The hydrostatic pressure at the orifice co will be equal F 2r> "k° ^ne weight of a column of water H less the weight of a column of kerosene of the same height, that is to say: 8 = H (Awater — Aj A designates the specific weights corresponding to the indices. But as this head must be given in meters of height of the liquid which is flowing, the expression for the head will be r —A; ^kerosene — * kerosene Aker< Introducing this value of h in the formula for the volume flowing, will give, for the volume of a light liquid (kerosene) flowing through an orifice into a heavy liquid (water), the following expression: AWater —2 (A) Passing to the case of the air and the gases in furnaces, this expression will become Q = r — Ag Agas in which H designates the distance from the lower free surface of the gas to the opening in the roof, or, as it may be said, the thickness of the layer of gas.