This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
238. The term fixture is applied to the apparatus which supports the gas burners and serves to connect them to the supply pipes. They are divided into three general classes: brackets, or side lights, which project from the walls; pendants, or chandeliers, which hang from the ceiling; and pillar lights, which stand upon a base, such as a mantel, a table, or a newel post.
Brackets made without joints are called stiff brackets, and those having flexible joints are called swing brackets.
All fixtures which hang from the ceiling may properly be called pendants; but, as commonly applied, this name is restricted to fixtures carrying one or two lights, and which are of plain construction. If the number of lights is greater, or the construction is decidedly ornamental, the term chandelier is used instead.
239. There is another class of fixtures called sun lights and constructed in a great variety of ways. They are used chiefly to produce a great amount of light near the top or ceiling of large audience rooms, and also to furnish copious illumination for show windows, etc.
A sun light consists of a large group of small gas burners, which are attached directly to the supply pipe, and a reflector, which is adapted to throw the light downwards as much as possible. The group is made up in a circle, or sometimes in a rectangle or in parallel lines. The burners are usually set so closely together that when one is lighted it will ignite the adjoining jets, and thus light up the whole group. The flames, however, should not touch each other when burning.
240. Common ornamental fixtures are usually built over a frame, or skeleton, of plain brass or iron tubing. The ornamental part consists of thin tubes, or shells, of brass, which are slipped over the main tubing, and are bound in place by screwing the various fittings tightly together. The best grade of fixtures, however, are made of solid brass or bronze.
241. An extension, or telescopic, chandelier is shown in Fig. 90. The fixture is provided with two tubes, an inner one a, which serves to conduct gas to the burners, and an outer one b, which has a cup c at the top end. The space between the tubes a and b is filled with liquid, and the supply pipe d dips below its surface at all times, thus preventing the gas from escaping. The pendant is held up by chains e and weights f, and it can be raised or lowered as desired. The chains are provided with stops to prevent the pendant from being lowered so far that the liquid may uncover the end of the pipe d. Instead of the chains and weights, coiled springs (like sash balances) are frequently used to sustain the fixture. The liquid may be either oil, glycerine, or mercury; water is unsuitable because it evaporates rapidly.
242. The chandelier just described was formerly much in use, but in recent years it has given place to that shown in Fig. 91. The liquid seal is replaced by a stuffing-box g, which is attached to the top of the sliding tube k, and which slides gas-tight over the supply tube h. The outer tube m is provided with a collar n, which guides the draw tube k and prevents dust from entering the interior and settling upon the surface of the tube h. The lubrication of the tube and stuffingbox can thus be maintained for a long time. As the tube h has only to supply gas, it can be made quite small in diameter. The devices used for balancing or sustaining this fixture in position are of many kinds. One of the best of these is a friction clutch which permits the draw tube to slide upwards without resistance, but which grips it and prevents it from moving downwards, except when pulled down by force.