118 NON-METALS AND THEIR COMBINATIONS. 



Other chlorides, such as those of potassium, magnesium, calcium, 

 also are found in nature. As common salt, chlorine enters the animal 

 system, taking there an active part in many of the physiological and 

 chemical changes. 



Preparation of chlorine. Most methods of liberating chlorine 

 depend on an oxidation of the hydrogen of hydrochloric acid by 

 suitable oxidizing agents, the hydrogen being converted into water, 

 whilst chlorine is set free. 



As oxidizing agents, may be used potassium chlorate, potassium 

 bichromate, potassium permanganate, chromic acid, nitric acid, and 

 many other substances. 



The most common and cheapest mode of obtaining chlorine is to 

 heat manganese dioxide, usually called black oxide of manganese, 

 with hydrochloric acid, or a mixture of manganese dioxide and 

 sodium chloride with sulphuric acid : 



Mn0 2 -f 4HC1 = MnCl 2 + 2H 2 O -f 2C1. 



Chlorine is liberated also by the action of sulphuric or hydro- 

 chloric acid on bleaching-powder, which is a mixture of calcium 

 chloride and calcium hypochlorite : 



CaCl 2 .Ca(ClO) 2 + 2H 2 SO 4 = 2CaSO 4 + 2H 2 O + 4C1. 



Experiment 13. Use apparatus as in Fig. 8, page 86. Conduct operation in a 

 fume-chamber. Place about 50 grammes of manganese dioxide in coarse 

 powder in the flask, cover it with hydrochloric acid, shake up well to insure 

 that no dry powder be left at the bottom of the flask, apply heat, and collect 

 the gas in dry bottles by downward displacement. Keep the bottles loosely 

 covered with pieces of stiff paper while filling them. Use the gas for the 

 following experiments : 



a. Fill a test-tube with chlorine, a second test-tube of same size with hydro- 

 gen ; place them over one another so that the gases mix by diffusion, then 

 hold them near a flame ; a rapid combustion or explosion ensues. 



b. Hold in one of the bottles filled with chlorine a lighted wax candle, and 

 notice that it continues to burn with liberation of carbon. The hydrogen con- 

 tained in the wax is in this case the only constituent of the wax which burns, 

 i. e., combines with chlorine. 



c. Moisten a paper with oil of turpentine, C 10 H 16 , and drop it into another 

 bottle filled with the gas ; combustion ensues spontaneously, a black smoke of 

 carbon being liberated. 



d. Drop some finely powdered antimony into another bottle, and notice that 

 each particle of the metal burns while passing through the gas, forming white 

 antimonous chloride, SbCl 3 . 



e. Pass some chlorine gas into water, and suspend in the chlorine water thus 

 formed colored flowers or pieces of dyed cotton, and notice that the color fades 

 and in many cases disappears completely in a few hours. 



