closed up, and the cover, or lid of the mouth of it secured by means of the wedge, in its place, so as to render the mouth of the retort perfectly air tight. There is a safety valve attached to this gasometer which could not be represented in the drawing; and the object of which is, to convey away any portion of gas that might happen to be produced by a careless operator, when the gasometer is full, and which is thus prevented from accumulating in the place where the gasometer is erected. It is represented in the right-hand corner of plate VII. where fig. 1 shows the edge of the gasometer; 2, the surface of the water in the inside of the gasometer; 3, the surface of the water in the outside of the gasometer, or in the cistern; 4, a pipe issuing from the lower edge of the gasometer, and surrounded at its upper extremity with a cup marked 5; 6, the waste pipe, the mouth of which is immersed in water. It is obvious that, when the gasometer is full, if an additional quantity of gas should be attempted to be put into it, it will be transported by means of the pipe 4, into the waste-pipe 6; the upper extremity of which reaches out of the building, and there communicates with the open air. PLATE II. Represents a Portable experimental Gas Apparatus for exhibiting, in the small way, the general nature of the gas-light illumination.--It is described page 79. PLATES III. IV. V. Show designs of various kinds of Gas Lamps, Chandeliers, Candelabras, &c.--See pages 114, 118, 140. PLATE VI. FIG. 1. Exhibits a design of the _gasometer framing_, or _skeleton_, which serves to give stability and strength to the gasometer. It consists of wooden frame work, marked A, A, A, interlaced with iron rods, B, B, B, &c. The whole framing is so disposed that it will float in the cistern horizontally, and therefore keep the gasometer perfectly steady and level with the surface of the water. The rest of the sketches represent various kinds of gas pipes employed as _mains_ for conveying the gas, and the methods of connecting them. FIG. 2. Represents a longitudinal section of a _Spigot_ and _Faucet Pipe_. These kinds of pipes are applicable in most cases as mains for conveying gas. A, is called the spigot, and B, the faucet. They are joined together, and made air tight, by iron cement, the composition of which is as follows: Take two ounces of sal ammoniac, one ounce of flowers of sulphur, and sixteen ounces of cast iron filings or borings. Mix all well together, by rubbing them in a mortar, and keep the powder dry. When the cement is wanted for use, take one part of the above powder, and twenty parts of clean iron borings or filings, and blend them intimately by grinding them in a mortar. Wet the compound with water, and when brought to a convenient consistence, apply it to the joints with a wooden or blunt iron spatula.