68 SCIENTIFIC AMUSEMENTS. 



Expt. 62. To obtain differently Coloured Solutions by dissolv- 

 ing the same body in different Solvents. Another remarkable 

 kind of exception to the above mentioned general rule is noticed 

 when differently tinted fluids are obtained by employing different 

 liquids to dissolve the same solid, no chemical change taking place 

 during the action.* Place in a small bottle a few small particles 

 of iodine (Expt. 50), and dissolve a few crystals of iodide of 

 potassium in a little water in another glass ; pour the colourless 

 solution of iodide of potassium into the bottle and shake up ; the 

 iodine will soon dissolve, forming a liquid of a yellowish brown 

 tint if sufficiently strong, and of lighter shades, somewhat 

 resembling sherry of various kinds, when weaker. (Similarly, 

 strong spirit of wine dissolves iodine, forming a " tincture " of iodine, 

 or alcoholic solution of iodine, of much the same range of colour as 

 before.) Now add a teaspoonful of chloroform to the watery fluid, 

 shake up, and then allow to stand a few minutes ; the chloroform 

 will soon settle at the bottom of the bottle, being a liquid which 

 will not readily dissolve in or mix with water (Chapter VIII.) ; but 

 before doing so it dissolves a large portion of the iodine, and in 

 consequence acquires a beautiful violet colour; so that you can 

 obtain two differently coloured solutions of iodine in the same 

 bottle one a solution in chloroform, of violet hue ; the other in 

 watery iodide of potassium, of brownish yellow tint. 



Expt. 63. Circumstances modifying the Rate at which Crys- 

 tals form from Solutions. Supersaturated Solutions. Some- 

 times when a hot saturated solution of a crystallisable substance is 

 cooled slowly and without agitation, it does not deposit crystals all at 

 once, but still remains clear and perfectly fluid, even though there is 

 more substance dissolved in the liquid than could be taken up by the 

 solvent at the temperature of the room by simply agitating it with 

 the crystallisable body. Sugar is one of numerous substances 

 exhibiting this property, to which the term Supersaturation is 

 applied. A very strong hot syrup, made by dissolving pure sugar 

 in boiling water, may often be cooled down completely without 

 depositing crystals; but on standing for some time the super- 

 saturated cooled liquid gradually forms crystals of sugar candy, 

 more especially on the surface of any foreign solid body introduced 

 for the purpose, such as the strings and sticks used in Expt. 58. 



The salt termed sulphate of sodium (or Glauber's salt) is a par- 



* When chemical changes take place during solution, as described later 

 on, all sorts of alterations in colour may take place under different circum- 

 stances ; thus the element called chromium (x(x^a = colour) derives its name 

 from the fact that by chemical action it can be converted into bodies of 

 most diverse colours, forming solutions of almost all the colours of the 

 rainbow. 



