110 APPLIED SCIENCE 



ice floats at 34 F. showing that it is lighter than water. 

 Careful investigation reveals that water is heaviest at 39 F. 

 (4 C.). 



111. Drying and Evaporation. The theory which under- 

 lies the process of drying is that dry air is capable of absorb- 

 ing moisture; hence by circulating currents of dry air in 

 and around wet substances, the absorbing power of the air 

 draws off the moisture. For continuous drying, free cir- 

 culation is a necessity, as air soon becomes saturated and 

 incapable of taking up more moisture. Warming the air 

 increases its capacity to absorb moisture; thus air at a high 

 temperature is capable of drying material much more quickly 

 than the same volume of air would at a low temperature. 

 A free circulation of air at 85 to 100 F., evenly distributed, 

 and with ample provision for the escape of the saturated air, 

 is essential for good drying work. 



Experience shows that when a liquid passes into a gaseous 

 state it absorbs heat from the surrounding bodies. To il- 

 lustrate: If a few drops of ether were placed on your hand 

 you would notice the ether disappear in the form of a vapor 

 by reason of the process termed evaporation, and your hand 

 would feel cold. Evaporation produces coldness. Experi- 

 ence also shows that in condensing a gas by pressing the 

 particles together, heat is given off. Thus the pressure on a 

 gas, that is, its compression, generates heat, while the libera- 

 tion of particles produces cold. 



All gases may be liquefied by increasing the pressure suffi- 

 ciently. If this pressure is suddenly removed the gas will 

 evaporate quickly and expand, thereby absorbing heat and 

 reducing the temperature of the surrounding bodies. 



These scientific facts are taken advantage of in refrigerat- 



