96 ANALYSIS AND SYNTHESIS PART i. 



substances may unite and form a third differing from both, 

 as water does from oxygen and hydrogen ; but if a new 

 substance be added which has a greater attraction for one 

 of the substances than for the other, it will dissolve their 

 union, combine with that for which it has the strongest 

 attraction, and set the other free. Thus the metal potas- 

 sium, which has a greater attraction for oxygen than t^ 

 hastfer hydrogen^ecomposes water, combines with the 

 oxygen, and sets the hydrogen free. Both chlorine and 

 ozone have the property of liberating the iodine in a 

 weak solution of the iodide of potassium; the liquid 

 stains starch blue, a proof of the free iodine. The faci- 

 lity with which acids and alkalies combine affords the 

 means of eliminating either the one or the other from 

 a compound so as to liberate what remains. 



The constituents of compound substances may be 

 separated from one another by a variety of means de- 

 pending upon their greater or less fusibility, volatility, 

 and other properties. Water, acids, alcohols and other 

 liquids hot or cold, different degrees of temperature, 

 sublimation, solution, distillation, evaporation, together 

 with static and voltaic electricity, are the most powerful 

 means of analysis. 



But the animal and vegetable creation rear their 

 fabrics by a synthetic process. A plant after having 

 absorbed carbonic acid and water, decomposes the car- 

 bonic acid, returns the oxygen to the atmosphere, and 

 combines the carbon and water into wood, leaves, and a 

 variety of organic substances. Now MM. Berthelot, 

 - Wohler, and other distinguished chemists, by following 

 this example of nature*, have established a system of 

 synthetic chemistry, by which they have produced from 

 the chemical combination of the three elementary gases 

 , and carbon alone more than 1,000 complete organic 

 | substances, precisely the same with those formed within 

 \ the living plants and animals. Yet we are as far as 



