34 SMITH'S INTERMEDIATE CHEMISTRY 



pressure. For oxygen this weight is 1.42900 grams (Morley). 

 The corresponding weight for air is 1.293, so that oxygen is slightly 

 heavier, bulk for bulk, than air (in the ratio 1.105 : 1). Oxygen 

 can be liquefied by compression, provided its temperature is 

 first reduced below 118, which is its critical temperature.* 

 The gas is only slightly soluble in water, the solubility at 20 being 

 3 volumes of gas in 100 volumes of water (at 0, 4.9 : 100). 



The solubility of oxygen in water, although slight, is in some 

 respects its most important physical property. Fish obtain oxy- 

 gen for their blood from that dissolved in the water. With air- 

 breathing animals (like man), the oxygen could not be so readily 

 taken into the system, if it did not first dissolve in the moisture 

 contained in the walls of the air sacs of the lungs, and then pass 

 inwards in a dissolved state to the blood. 



Liquid oxygen, first prepared by Wroblevski, has a pale-blue 

 color. At one atmosphere pressure, that is, in an open vessel, it 

 boils at - 182.5. Its density (weight of 1 c.c.) is 1.13, so that it 

 is slightly denser than water. By cooling with a jet of liquid 

 hydrogen, Dewar froze the liquid to a snow-like, pale-blue solid. 

 A tube of liquid oxygen is noticeably attracted by a magnet. 



Six Specific Physical Properties of Each Gas. Although 

 every substance has many physical properties, we shall mention 

 only those which are used in chemical work, with occasionally the 

 addition of any peculiar or unexpected quality. It will aid the 

 memory to recall the physical properties of a gas, if we note that, 

 as a rule, only six such properties are mentioned: (1) color, (2) 

 taste, (3) odor, (4) density, (5) liquefiability, defined by the 

 critical temperature, (6) solubility, usually in water only. 



* Each gas has an individual critical temperature (p. 91) above which no 

 pressure, however great, will produce liquefaction. The farther the tempera- 

 ture of a specimen of the gas is below the critical point, the less will be the 

 pressure required to liquefy it. 



