Page:Popular Science Monthly Volume 78.djvu/605

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vironment so that different plants and animals can be observed during several generations at specified and perfectly controlled temperatures. Four rooms are kept at + 5° C, + 10° C, + 15° C. and + 20° C. The carbonic acid machine (Fig. 14) produces 5,500 calories hourly.

PSM V78 D605 Over and under lighting apparatus.png

Fig. 12. Apparatus for Over and Under Lighting. d, compressed air; s, mirror; o, box, open above; p, box, open below; w, glass walls.

The fluid carbonic acid flows into a wrought-iron spiral core within a carefully isolated receptacle made of tin plate. The salt water surrounding the spiral core is cooled to a low temperature by the sudden

PSM V78 D605 Warm room with elevated temperature.png
Fig. 13. Warm Room with Compartment for Elevated Temperature on the Right.

expansion of the liquid carbon dioxid. Then the carbonic acid gas is compressed under 55 atmospheres and conducted into a wrought-iron spiral core in the condenser where it is again cooled, liquefied and ready to flow on in the continuous circulation through the machine.