126 



CHEMISTRY. 



[Lesson XII. 



Instead of collecting the gas over water as 

 usual, let the tube pass to the bottom of 



Fig. 35. 



the receiver, which should be loosely 

 covered with a piece of card ; by this means, 

 the chlorine will fill the bottle and displace 

 the air ; it may be collected over warm 

 water, but then the gas expands from the 

 heat. 



135. T. Why is not this gas collected 

 over water as usual ? 



P. Because cold water absorbs it. [Ex- 

 periment 26.] You observe that about 

 two-thirds of this bottle is occupied by 

 chlorine, and the rest by water. I will 

 shake it [does so, and the water dissolves 

 the chlorine], and now you see that the 

 yellow-green colour has disappeared, be- 

 cause we find that one part of water will 

 dissolve two parts of chlorine, forming what 

 is called chlorine water. 



136. T. As you have collected several 

 bottles of the gas, give some experiments 

 to illustrate its properties. 



P. Be careful not to come too near, 

 because this gas is very irritating, and if 

 inhaled, is injurious.* Now, you observe 

 that I have several discs of millboard, well 

 greased, to go over the tops of the bottles, 

 and also that each disc has a piece of 

 twisted wire passing through its centre. 

 [Experiment 27.] I will plunge this wire, 

 witli the lighted taper attached to it, into 

 the gas [does so] ; it burns with a dull 

 red light, and is now extinguished. [Ex- 

 periment 28.] This wire has a piece of 

 gold leaf attached; see how vividly it burns 

 now that it is placed in the gas. [Experi- 



* When experimenting with chlorine, it is ad- 

 visable to sprinkle a strong solution of ammonia 

 about the table, and also to have a cloth moistened 

 with it, near to the operator. 



ment 29.] Here is some metallic anti- 

 mony in line powder [pours it into the jar 

 of the gas] ; now see what a beautiful 

 shower of iire it produces. [Repeat Ex- 

 periment 28, using copper leaf instead, and 

 plunge phosphorus in the gas for another 

 experiment.] 



137. T. What other properties does 

 it possess ? 



P. It is a powerful bleaching and dis- 

 infecting agent, which results from its 

 strong affinity for hydrogen. [Experi- 

 ment 30.] This wire holds a sprig of 

 damp parsley ; let us see what will be the. 

 effect of plunging it into the gas. [Places 

 it in the jar]. It has lost its beautiful 

 green colour, and is rapidly becoming- 

 white. 



138. T. What is IODINE? 



P. A solid body, which looks very like 

 plumbago or black-lead, and smells like 

 chlorine. Its name is derived from the 

 Greek word iodese, (iwSijs), violet-coloured, 

 and its specific gravity is 4-948. 



139. T. Give some illustrations of its 

 properties. 



P. [Experiment 31.] I have placed a 

 few grains of iodine into a flask ; observe 

 what a beautiful violet colour it gives out 

 when heated over a spirit-lamp. [Ex- 

 periment 32.] This tumbler contains a 

 solution of starch, made with hot water, 

 and allowed to cool ; observe wluu 

 place when I add this very small piece of 

 iodine and stir the starch. [Does so, and the 

 starch changes to a beautiful blue colour]. 

 This last experiment proves the value of 

 starch as a test for iodine. 



140. T. How is iodine procured ? 



P. From help, or the half-vitrified ashes 

 of sea-weeds ; but the process is too long 

 to enter into. 



141. T. What is BROMINE? 



P. It is a deep brownish-red liquid, 

 with a very foetid, disagreeable odour, as 

 its name implies, being derived from the 

 Greek word bromos, (fipwfjios), a noisome 

 smell. Its specific gravity is 3. 



142. T. How is bromine obtained? 



P. From sea water ; but the process is 

 too long to describe ; suffice it to say that 

 chlorine is used to decompose the bromide 

 of magnesium, in which form it is generally 

 found, and that ether is then added, and 



