RECOGNITION OF AN ORGANIC COMPOUND. 



Organic compounds are distinguished from inorganic compounds 

 by being combustible: on heating they generally char, sometimes 

 take fire, and on prolonged heating completely burn away leaving 

 no ash. Inorganic compounds when heated do not char and they 

 leave a residue. A mixture of an organic compound and an inorganic 

 compound will also char and leave a residue. There are a few excep- 

 tions to this general rule : oxalic acid and its salts amongst the organic 

 compounds do not char on heating ; amongst the inorganic com- 

 pounds the ammonium salts volatilise leaving no ash. An oxalate 

 leaves a residue of the oxide of the metal with which it is combined. 



The following experiments exemplify these statements : 



1. A small piece of paraffin wax heated upon platinum foil will melt, take 

 fire, and will completely burn away leaving no residue. 



2. A crystal of cane sugar heated in the same way will melt, char, and 

 on further heating will disappear completely. 



3. A few crystals of common salt heated on platinum foil will melt, and 

 unless heated very strongly, e.g. with a blowpipe flame, will remain as a solid 

 white mass when allowed* to cool. 



4. A small piece of soap heated as above will char, the vapours evolved 

 may take fire, and when the charred particles have all vanished a white or 

 nearly white residue will R-rmin. 



Note. // is in this way that substances composed of organic and inorganic 

 matter are recognised. The composition of the inorganic residue is found out by 

 the usual m 'thods of inorganic analysis after the organic matter has been destroyed 

 by heating. 



5. No appreciabl- will be seen on heating a little oxalic acid or an 

 o, e.g. calcium oxalate. 



6. Ammonium chloride volatilises on heating and leaves no residue. 



7. To prove the presence of carbon in oxalic acid or in an oxilate the sub- 



!K a'u-tl in a smull glass tube and the gases evolved are passed into 

 or hiryta water. A precipitate of calcium or barium carbonate indicates 



1 carbon. 



8. On h.-atin^ ammonium chloride as in 7, there is no formation of 

 carbonate. 



