140 



NON-METALS AND THEIR COMBINATIONS. 



sels) filled with water. Notice that a strip of wood, a wax candle, or any other 

 substance which burns in air. burns with greater energy in oxygen, and that 

 an extinguished taper, on which a spark yet remains, is rekindled when placed 

 in oxygen gas. Notice, also, the physical properties of the gas. If the decompo- 

 sition has been too rapid by using too large a flame, the gas will appear cloudy, 

 due to the dragging over of some of the contents of the flask by it. The cloud 

 will disappear upon standing. 



CAUTION. In all experiments of this kind, where a vessel is filled wiih a hot gas, 

 the exit tube should be removed from water before removing the flame, to prevent water 

 from being drawn back into the vessel as the gas cools and contracts. 



Experiment 2. In a porcelain crucible held in a pipe-stem triangle, place a 

 layer of potassium chlorate about J inch deep. Heat moderately at first until 



Apparatus for generating oxygen. 



frothing ceases, and then gradually to low red heat. Cool and dissolve the 

 residue in a little water in the crucible, warming to hasten solution. Taste the 

 solution. Does it taste like common salt (sodium chloride)? Compare with 

 the taste of potassium chlorate. Pour some of the solution into a test-tube and 

 add a few drops of a solution of silver nitrate. Do the same with a solution of 

 common salt. The white clotted substance, known as a precipitate, is silver 

 chloride, and is given by all soluble chlorides. Also add some silver nitrate 

 solution to a solution of a little potassium chlorate. Is any precipitate formed? 

 All chlorates are soluble. 



Physical properties. Oxygen is a colorless, inodorous, tasteless 

 gas, slightly heavier than air. Under a pressure of 50 atmospheres, 

 and at a temperature of -118 C. (-180.4 F.) it condenses to a 

 transparent, pale-bluish liquid, which under ordinary atmospheric 

 pressure boils at -183 C. (-297.4 F.). Its absolute boiling-point, 

 above which it cannot be condensed to a liquid by any pressure, no 

 matter how high, is -118 C. (-180.4 F.). 



