Page:Popular Science Monthly Volume 78.djvu/605

Rh 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.

 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

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.