The Proctor incubator, made at Otley, is apparently, in its main features, similar to the Greenwood.
| Fig. 6.—The Winchcombe Incubator. |
Somewhat similar, in certain features, to the Greenwood is the Winchcombe. Its improved form, in which metal replaces the wood casing, is named the Gladstone. In it there is a combination of the hot-air and the water-tank systems of warming the incubation chamber. The wall of the incubator is double, and the space between the outer and inner wall is packed with a non-conducting material. The incubation chamber is heated above by a water-tank (fig. 6 T) which is traversed by a main vertical flue (F) and four subsidiary horizontal ones which discharge externally. The main flue, however, in passing up to enter the water tank traverses the egg-chamber, and therefore serves to warm it, as in the hot-air type of incubator, by the heat of the flue itself. Around the lower half of the flue is a water vessel consisting of two concentric containers (C), holding water. In the space between these concentric containers, fresh air passes in through the aperture (A), and before it reaches the egg-chamber it passes through coarse canvas which dips into the water in the containers, and is therefore kept permanently moist. The containers are filled from a water tank (S) outside the incubator. Air passes out from the egg-chamber through the aperture (O). The temperature is regulated by a bimetallic thermostat (see below), which operates two levers, that by their arrangement can raise or depress the cap (D) over the main flue (F). The temperature at which this occurs will be determined, within limits, by the position of the adjustable weight (W).
Tomlinson’s incubator, designed in 1880, is novel in principle. It possesses a very large water tank, holding 15 gallons for every hundred eggs. Through this tank there pass two hot-air horizontal flues, lying in the same plane. The novelty of the construction lies in the great volume of water used and in the disposition of the flues towards the top of the tank. It is said that very little circulation of water takes place beneath the flues, because warmed water rises instead of falling. The great body of water below the flues will therefore only take up heat relatively slowly, and will, on account of its bulk and its physical properties, but slowly lose it. Should the flame fall in power, or even go out for ten or twelve hours, it is claimed that no serious loss of efficiency of the apparatus will result.
Regulation of the temperature is by means of an air tube, the air in which expanding bulges out an india-rubber diaphragm and this moves a lever. The lever operates a valve which allows more or less of the heated air to escape from the egg-drawer.
| Fig. 7.—Hillier’s Incubator. |
(b) Hot-air Incubators.—W. H. Hillier’s Incubator (fig. 7) is circular in form and is constructed of a double-walled metal case. The space between the two walls is packed with a non-conducting material. The incubation or egg-chamber (C) is warmed by a circular heating box (H), and the air in this is heated by a lamp. The roof of this box forms part of the floor of the incubation chamber and from it a main flue (F) and four smaller ones (F′) pass upwards through the roof of the incubator and discharge to the exterior. Fresh air passes in to the incubator through two tubular channels (A and A′) on either side of the heating box and escapes through a hole in the roof, which serves at the same time as a passage for one of the rods (D) in connexion with the temperature regulating apparatus.
This apparatus (T) consists of a glass tube of ½ in. bore, and which is bent into the form of a circle of 5 in. diameter. The tube is fastened to a wooden disk, which rotates upon a pivot and in so doing operates a vertical rod (D), which in its turn works the cap (V) which covers the orifice of the main flue. The tube is partly filled with mercury and is closed at one end. At this end there is contained some spirit. As the temperature rises, this expands and pushes the mercury column farther along the tube. The equilibrium of the position of rest is thus disturbed, and the wooden disk consequently rotates, carrying with it the vertical arm, the downward movement of which raises the cap (V) of the flue. The temperature at which it is desired that this valve shall uncover the flue, can be adjusted within the necessary limits by sliding the weight (W) along the horizontal arm and by the amount of mercury present in the bent tube. The air of the incubation chamber is rendered sufficiently moist by the evaporation of water in the vessel (G).
In the Cornell incubator (New York) more personal attention is required than in other forms, since the ventilation of the egg-chamber is not wholly automatic but is regulated according to the results of observation. The great difficulty in ventilation is the proper combination of fresh air and moisture. The Cornell Incubator Company has endeavoured to obviate this difficulty by carrying out a series of observations on the rate at which evaporation occurs in incubating eggs under natural conditions. The rate of evaporation is measured by the size of the air-space within the egg-shell at successive days. This they have ascertained, and with their incubators they furnish a book of instructions in which diagrams showing the size of the air space on the 1st, 5th, 10th, 14th and 18th days are given. Examination of the eggs should therefore be made every two or three days, and the result compared with the diagrams. The incubator is provided with an adjustable ventilator and this should be so arranged that evaporation is neither too great nor too little. The ventilator should never be wholly closed, and if when closed to its minimum evaporation is still too great, then water should be placed in the moisture pans. In all cases lukewarm water should be placed in these on the 18th day and the ventilating slide opened wide.
It will thus be seen that in this machine there is an attempt to do away with the addition of water to the incubator drawer during the greater part of the period of incubation, and to rely upon the aqueous vapour naturally present in the atmosphere. This attempt is based upon the fact that water vapour is lighter than air, and will therefore rise to the top in any enclosed volume of air. If the direction of the ventilating current is downwards in the incubation chamber, and if it is slow enough, it is thought that the water vapour will be sifted out and tend to accumulate to a sufficient extent in the chamber. In the Cornell incubator consequently the ventilating current passes first upward through an external heater in order to warm it, whence it is then deflected downwards into the egg-chamber and diffuses through its perforated bottom. Then it passes along a space beneath the chamber into a space in the left-hand wall of the incubator and out to the exterior through an adjustable and graduated ventilating slide.