170 CHEMICAL DISCOVERY AND INVENTION 



twenty times the amount required by this hypothesis ; therefore 

 after all the temperature of the earth may be actually rising and 

 not falling, and the consequence is that evidence as to the age of 

 the earth is still very nebulous. 



CHAPTER IX 



SOLUTIONS 



PKOBABLY few persons as they drop the sugar into a cup of tea 

 concern themselves with the problem which is presented by the 

 disappearance of the lump and the fact that in a few minutes, 

 even without stirring, the taste of the sugar can be recognised 

 in every part of the liquid. Suppose the sugar to be immersed in 

 water the change can be watched more readily, and it is at once 

 seen that the crystalline mass falls quickly asunder, while a 

 dense syrupy liquid streams away from it. After a time, if 

 sugar is added in successive portions to the same quantity of 

 water, the process of dissolution slackens, the lumps crumble 

 away less rapidly, and ultimately they undergo no change, the 

 liquid being then, to use the common expression, saturated. 



But every cook knows that if heat is applied and the tem- 

 perature of the liquid raised more sugar will dissolve until 

 another point of saturation is reached as the liquid boils. If 

 such a liquid is then allowed to cool to the temperature of the 

 air a portion of the sugar soon begins to separate from the 

 liquid in the form of crystals the size of which depends on the 

 volume of liquid and the condition whether it is stirred about or 

 left at rest. 



A lump of white marble looks to the unaided eye so much like 

 loaf sugar that it might easily be mistaken for that substance, 

 but if a lump of white marble is placed in hot tea or cold water 

 no change would be observed ; it would not dissolve. But now 

 suppose that the lump of white marble is immersed in water to 

 which some nitric or hydrochloric acid has been added, there 

 will be a great effervescence, bubbles of gas (carbon dioxide) 

 escape, and the marble rapidly disappears, forming a clear 

 colourless solution. This solution, however, contains something 

 different from marble, and if the liquid is duly concentrated it 

 \\ill yield crystals, quite unlike marble, which consist of the 



