146 SCIENTIFIC AMUSEMENTS. 



Expt. 151. To produce White Indigo and convert it into Blue 

 Indigo by the action of the Air. Put into a bottle (capable of 

 being tightly closed with a cork) some indigo solution (sulphin- 

 digotic acid), and dilute it with water, so as to obtain a moderately 

 deep blue-coloured liquid. Add a tablespoonful of quicklime and 

 half as much glucose (grape sugar). Tightly cork the bottle, and 

 let it stand some hours, with occasional shaking ; a chemical action 

 will take place, resulting in the conversion of the blue indigo into 

 " white indigo "), so that the colour of the liquid fades. By and 

 by, when the blue has disappeared and a yellowish liquor only is 

 contained in the bottle above the sediment, the clear liquor may 

 be decanted into a cup ; by exposure to air it will gradually take 

 up oxygen (like the pyrogallic acid dissolved in potash in the last 

 experiment), and the blue colour will be restored. 



Into the yellow fluid dip a piece of white flannel or a skein of 

 white Berlin wool, and then hang it up wet for some time ; as the 

 blue indigo is formed by the action of the air on the white indigo 

 solution, it becomes attracted to and fixed in the substance of the 

 woollen fibres, permanently dyeing them blue. This is substantially 

 the way in which indigo-dyed woollen cloth is usually prepared. 



Production of Precipitates by Solution of Gases in Liquids. 



This class of chemical action is of very frequent occurrence; 

 thus the test employed in Expt. 147, for the presence of carbon 

 dioxide, when mixed with other gases, is based upon a reaction of 

 this kind. 



Expt. 152. To make a Clear Fluid, apparently Water, re- 

 semble Milk by dissolving a Gas therein. Get a little quicklime 

 (an ounce or less will suffice), and pour on it a few drops of water ; 

 if freshly burnt, it will become hot, and by and by fall to powder. 

 This is called "slaking" the lime, and is due to a chemical action 

 taking place between the quicklime and the water (Expt. 240) ; 

 with large quantities of lime a very high degree of heat can be 

 thus produced, so that wood has been known to be charred and 

 similar damage done, as though by fire, when water has accidentally 

 come in contact with large stores of quicklime. Shake up the 

 slaked lime several times in a clear wine bottle nearly filled with 

 soft water, or preferably distilled water, cork the bottle, and let it 

 stand some hours, shaking it up occasionally. Next day pour off 

 from the sediment the clean lime-water , or watery solution of lime, 

 produced, and keep it for use in a well-closed bottle. Fill 

 a small jar with carbon dioxide by displacement (Expt. 101) ; 

 set it on the table mouth upwards, and pour in a wine-glassful 



