Automatic Burner Operated by Door.
One of the uses to which an automatic burner can be put is in conjunction with an electric door-spring, lighting when the door is opened, but preferably extinguished by independent push. In this case, a form of trip spring should be used which would only make contact during a portion of the travel of door. Such a trip is shown in Fig. 26.
A is automatic burner; C, the primary coil; B, the battery; T, a swinging trip piece of brass hinged in brass plate, P, which is screwed over the door in such manner that the door opening in direction of the arrow will cause the trip T to strike against the spring S, and make contact. This spring is insulated from the plate P by the hard rubber block R.
On the door being opened, the trip will make contact long enough to light the burner and will then fall back as the door passes. On shutting the door, the trip will be raised and will fall as the door passes, but will not make contact. Or, if so desired, it can be made to operate a second contact to extinguish the burner by fixing a second insulated spring so it will be pressed when the top of trip makes a downward movement—as when the door passes it in shutting.
Fig. 26.
Various applications of automatic burners in connection with burglar alarms will suggest themselves, but in these cases the utmost care must be taken that the apparatus is in good working order; failure to light might cause the room to be filled with gas, and serious results ensue.
For those persons who use gas stoves and are mechanically inclined, an arrangement of an alarm clock with an automatic burner will enable them to light up without getting out of bed, or perhaps even waking up.
CHAPTER IV.
Primary Coils and Safety Devices.
To construct a primary coil such as used with pendant or automatic burners presents no difficulty. The most convenient sizes are those 8 to 10 inches in length and about 3 inches in diameter. It is quite common to speak of these coils as 8 or 10 inch coils; to the writer’s knowledge this has been taken to mean a Ruhmkorff or double-wound induction coil, giving a free 8 or 10 inch spark.
Fig. 27.
To make such a coil (Fig. 27), proceed as follows: Prepare a spool by gluing a paper or fibre tube 3/4 inch in outside diameter by about 1-16 inch thick into square or round spool ends three inches square, one-half inch thick, and having each a centre hole just large enough to admit of the tube being held tightly. These ends should be firmly fixed on the tube; a pin or two driven through tube into end will assist in strengthening the joint. Now wind on the tube about 3 pounds No. 12 B. & S. cotton-covered magnet wire. This will give about six layers of 80 turns each, nearly 500 turns in all, a total length of, say, 150 feet, measuring .25 ohm. The ends of the wire are to be brought out through holes drilled in the spool ends, and can be fixed to brass binding posts on those ends.
Into the paper tube push as many iron wires 8 inches long by No. 22 B. W. gauge as will fill it. These iron wires can be tightened finally by driving in at each end, a stout wire nail.
Although not absolutely necessary, a coat or two of shellac varnish applied to the windings will make a better insulation. Shellac varnish is readily made by dissolving one part gum shellac in four parts of alcohol. For coils which are likely to be in damp places, a good saturation with insulating compound, such as P. & B. paint, will render them waterproof. The need for good insulation in these primary coils is not so urgent as in Ruhmkorff coils, owing to the lower potential of the current.
A smaller coil can be made with No. 14 B. & S. wire where the battery is of higher resistance (or gives less than ten amperes on short circuit). The remarks on battery selection on another page will be found to meet application here.