use about 1845, and in his hands it appeared occasionally to act
successfully, but it never became generally used. The egg chamber
was lined with felt, and was placed beneath a heated air chamber,
the floor and roof of which were composed of glass. The air chamber
was heated by a number of hot-water pipes which were connected
with a copper boiler. This latter was heated by means of a lamp
so constructed as to burn steadily. The temperature of the air
chamber was regulated within certain limits by means of a balanced
valve, which could be so adjusted that it would open at any desired
temperature.
In Colonel Stuart Wortley’s incubator the hot-water tubes passed directly into the egg chamber, and in Brindley’s into a chamber above it. But in other forms of incubators in which the principle of an external boiler connected with water tubes is adopted, the latter pass not into the egg chamber nor into an air chamber, but open into and from a tank of water. The floor of this tank forms the roof of the egg chamber, so that the eggs are heated from above. This device of warming the eggs from above was adopted in imitation of the processes that presumably occur with the sitting hen; for it is generally assumed that the surface of the eggs in contact with the hen is warmer than that in contact with the damp soil or with the material of the nest.
One of the earliest of this form of incubator is that invented by F. Schröder, manager of the now extinct British National Poultry Company. In this incubator the form is circular, and there are four egg drawers, so that each one occupied the quadrant of a circle, and the inner corner of each drawer meets in the middle of the incubator. From the centre of the incubator a vertical chimney passes upwards and opens out from the inner corners of the four egg drawers. This chimney acts as a ventilator to the incubating chambers. These latter are open above, but their floors are made of perforated zinc, and when in use they are partially filled with chaff or similar material. Under them is a tank containing cold water and common to all four drawers; the slight vapour rising from the surface of the water diffuses through the egg drawers and thus insures a sufficient degree of humidity to the air within. Above the egg drawers is a circular tank containing warm water. The floor of this tank constitutes the roof of the egg drawers, while the roof forms the floor of a circular chamber above it, the side wall of which is composed of perforated zinc. This upper chamber is used to dry the chicks when they are just hatched and to rear them until they are strong enough for removal. It is partially filled with sand, which serves the double purpose of retaining the heat in the warm-water tank beneath and of forming a bed for the chicks. The water in the warm-water tank is heated by means of a boiler which is external to the incubator, and in communication with the tank by means of an inlet and an outlet pipe. There is no valve to regulate the temperature, and the latter is measured by means of a thermometer, the bulb of which is situated not in the incubator drawers, but in the warm-water tank. This is a wrong position for the thermometer, since it is now known that the temperature of the water tank may be different by several degrees to that of the egg drawer; for with a fall of external temperature that of the latter necessarily tends to fall more rapidly than the former. But, none the less, in skilful hands this incubator gave good results.
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| Fig. 1.—Christy’s Improved Incubator. |
T. Christy’s incubator, which we shall describe next, has passed through several forms. We shall consider the most recent one (1894). The incubator (fig. 1) is double walled, and the space between the two walls is packed with a non-conducting material. In the upper part of the incubator there is a water tank (T) divided by a horizontal partition into two chambers, communicating with each other at the left-hand side. Below the tank is the incubation drawer (E), which contains the eggs and also a temperature regulator or thermostat (R). The tank is traversed by a ventilating shaft (V), and inserted into this is a smaller sliding tube passing up to it from a hole in the bottom of the incubator drawer. The floor of the incubator drawer is perforated, and beneath it is an enclosed air space which opens into the sliding air shaft just described. Fresh air is let into the incubator drawer from a few apertures (I) at its top. The ventilating shaft (V) is closed externally by a cap (C), which can be raised from or lowered down upon its orifice by the horizontal arm (H) working upon pivot joints at (P). This arm is operated by the thermostat (R), through the agency of a vertical rod. The water in the tank is heated by an external boiler (B) through two pipes, one of which (T) serves as an inlet, and the other (L) as an outlet channel from the tank. These two pipes do not open directly into the tank, but into an outer vessel (O) communicating with it. Communication between this vessel and the tank may be made or broken by means of a sliding valve (S), which is pierced by an aperture that corresponds in position with the upper of the two in the wall of the tank when the valve is up. When this valve is in its upper position, the tank (T) communicates with the outer vessel (O) by two apertures (A and A′), the top one being the inlet and the lower one the outlet. These coincide in position with the tubes from the boiler. This latter (B) is a conical vessel containing two spaces. The heated water is contained in the outer of these spaces, while the central space is an air shaft heated by a lamp flame. This particular form of the boiler results in the water at its top part being more heated than that in its lower. As a consequence of this, a continual circulation of water through the tank ensues. The more heated water, being specifically lighter, passes into the outer vessel, where it remains among the higher strata, and therefore enters the tank through the upper aperture. In passing along the upper division of the tank it becomes slightly cooled and sinks therefore into the lower compartment, passes along it, and out through the aperture A′. Hence it passes into the lower portion of the boiler, where it becomes warmed and specifically lighter; in consequence it becomes pushed upwards in the boiler by the cooler and heavier water coming in behind and below it.
Should the temperature in the incubator drawer rise, the bimetallic thermostat (R) opens out its coil and pulls down the vertical rod. This simultaneously effects two things: it raises the cap (C) over the ventilating shaft and allows of a more rapid flow of fresh air through the incubator drawer, and it also lowers the slide-valve (S) so that the tank becomes cut off from communication with the outer vessel (O) and therefore with the boiler. The temperature thereupon begins to fall and the thermostat, coiling closer, raises the vertical rod, closes the ventilating shaft, and once more places the tank in communication with the boiler.
The structure of the thermostat is given below.
The Chantry Incubator (Sheffield) is also an incubator with a hot-water tank, the circulation of which is maintained by an outside boiler. Its temperature is regulated by a metal regulator.
In Schröder’s and Christy’s incubators the hot-water pipes from the boiler simply entered the warm-water tank but did not traverse it. In the two incubators to be next described the hot-water pipes are made to pass through the water in the tank, and are so arranged as to minimize the possibility that the outside of the tank may become colder than the centre. Both of them are also fitted with an ingenious though slightly complex valve for maintaining an approximately constant temperature.
Halsted’s incubator was the earliest of this type. Since his original form was constructed he has designed an improved one, and it is this latter which will be described.
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| Fig 2.—Halsted’s Incubator. |
The egg drawer (E, fig. 2) lies beneath the warm-water tank (T), and above this is a nursery (N). The egg drawer is ventilated by two tubular shafts (V), of which only one is represented in the illustration; the tubes are about 212 in. in diameter, and each one is fitted at its upper end, where it opens into the nursery, with a swing-valve (V′) which turns upon a horizontal axis (A), in its turn connected, by means of cranks (C) and shafts (S), with the heat regulating apparatus (R). A space of about 2 in. between the top of the incubating drawer and the warm-water tank is necessary for the insertion of this apparatus. The water in the tank (T) is heated by means of the boiler (B); the tank and boiler are connected by the two pipes (I) and (O), of which one is the inlet and the other the outlet channel. The boiler consists of an inner (I′) and an outer (O) division in communication with each other below. The latter is cylindrical in form, while the outer wall of the former is cylindrical and its inner wall conical. The conical wall of the inner boiler is the surface which is heated by the lamp (L). The arrangement of the inlet and outlet tubes is important. In the illustration, for the sake of clearness, they are represented as one above the other. In reality they lie in the same plane, and the fork (F) of the inlet pipe similarly lies in the horizontal plane and not vertically as represented. The inlet pipe not only differs from the outlet pipe in the
