We take it for granted that our readers know generally how glass is made. That a mixture of sand and an alkali is fused into a kind of pasty mass. The fusion is effected in pots of refractory clay, of which the general form is something like that shown in the sketch. The mouth of the pot is shown at A. The pots at Val St. Lambert are of various sizes; the largest hold about 16 cwt. of glass. The duration of the pots is very variable; they last sometimes only a few days, at others several weeks or even months, much depending on the quality of the pot. The temperature to which they are exposed is not excessively high. The great thing to be effected in a glass melting furnace is the perfectly equal distribution of the heat. At Val St. Lambert gas is used, generated in Siemens or Boetius producers. There are in all twenty furnaces. They are grouped in threes or fours, in the large buildings, with high roofs. Formerly the furnaces were square, and held each eight melting pots, which did not hold more than 250 kilos. of glass. The modern furnaces each receive from twelve to fourteen melting pots. The modern melting pots as made by the Battersea Plumbago Crucible Company do not seem to be known here. [Illustration] The peculiarities of the construction of the glass melting furnaces at Val St. Lambert will be gathered from the annexed sketch. The furnace is circular, 14 ft. or 15 ft. in diameter, and from the roof, E, to the floor is about 5 ft. 6 in. high. In the center of the floor is a cylindrical opening, A, through which rises the mixture of gas and air, the latter being introduced through four openings, three of which are shown. Two of the pots are indicated by dotted lines at D D. The equitable diffusion of the heat is effected in the following way: Inside the furnace are constructed as many vertical flues as there are pots. Two of these are shown at G G. They have small openings about 5 in. by 8 in. at the bottom. The course pursued by flame is indicated by the bent arrows. The flame rising strikes the crown, E, and is deflected downward and drawn off by the side flues, which deliver into the second vaulted space, F. In this, in some cases, are annealed the finished articles of glass. In others is fixed a boiler, steam being generated by the waste heat. In others there is no opening at the top of F at H, but there is one at the side instead, through which the flame is led to raise steam in Belleville tubulous boilers. The steam is used to drive the engines in the grinderies. Not much power is required, and it is very easily obtained from the waste heat. [Illustration: SECTION OF CLASS FURNACE]