TSU AoniCULTVUAL JoVltNAL. 



777 



Agricultural Chemistry for Beginners, 



CHAPTER VII. 



By Archibald Pearce. 



ORGANIC MATTER 



IF we examine a portion of any living 

 thing, whether plant or animal, it 

 will be noticed to consist of various well- 

 defined parts such as tubes^ hairs, mem- 

 branes, etc., to which the name of organs 

 is given; and matter in this, which may 

 be considered its highest form, is said 

 to be organised. But organised matter is 

 composed of various compounds; and to 

 these substances, the materials of which 

 organised matter is built up, the term 

 organic matter is applied. At one time 

 it was believed that no organic compounds 

 could possibly be obtained without the 

 agency of life in seme form or other, and 

 so a sharp line of distinction was drawn 

 between organic and inorganic or min- 

 eral matter; but of late years it has been 

 discovered that many organic compounds 

 can be built uj) from inorganic nuiterials, 

 and so the dividing line is not very de- 

 finite. But still the term is practically 

 a very convenient one; and the chemist 

 understands that in speakiilg of organic 

 substances he is referring to such chemi- 

 cal compounds as are derived from 

 animal or vegetable matter, even 

 if in any special case they 

 happen to have been artificially 

 produced from inorganic sources. There 

 is this restriction x^'hich miftst be placed 

 upon the preceding definition, namely, 

 that all organic substances arc compounds 

 of the element carbon. This limitation 

 is best illustrated by an example. We 

 have learnt that when nitrogenous ani- 

 mal or vegetable matter — ^vve will now 

 call it nitrogenous organic matter — de- 

 cays, one of the products formed is al- 

 ways ammonia, and it might be thought 

 that this ought to be classed as an organic 

 compound; but the original matter con- 

 tained no ammonia as such, and it was 

 only produced owing to the processes of 

 decay causing the original compounds to 

 re-arrange their elements and form new 

 combinations. Organic matter, then, may 



AND CARBON. 



be defined as the carbon compounds which 

 are found in animal or vegetable struc- 

 tures or are derived from those struc- 

 tures. The number of these compounds 

 is legion; in fact they far outnumber all 

 the compounds of other elements put to- 

 gether, and some of them are of very 

 complicated construction! The chief 

 elements that go to the formation of these 

 organic compounds with carbon are oxy- 

 gen, hydrogen, nitrogen, and in a less 

 degree, phosphorus and sulphur. Or- 

 ganic matter, if heated in the air, first 

 blackens, owing to the separation of car- 

 bon; and if the heat be increased, and 

 the supply of oxygen kept up, it is gradu- 

 ally converted into various gaseous com- 

 pounds, which disappear in the form of 

 smoke, etc. We are all familiar with the 

 result of burning organic matter such as 

 wood; the organic portion is entirely 

 burnt away, as we say, and only a small 

 residue of mineral matter is left, which 

 we call ash. 



Carbon. 



No one, on a casual inspection, would 

 be likely to imagine that a diamond, the 

 lead from a pencil, and a piece of char- 

 coal were identically the same substance; 

 and vet such is the fact, all three being 

 different forms of the element carbon. 

 The diamond is crystallised, or has a de- 

 finite geometrical shape; the others are 

 amorphous, or without crystalline form. 

 It is true that charcoal is not quite pure 

 carbon, containing, as it does, a small 

 quantity of mineral ash; but this in no 

 way alters its appearance, as may be seen 

 by charring a piece of pure sugar, when 

 pure carbon remains. 



Carbonic Acid. 



When carbon is burned, it unites with 

 the oxygen of the air, forming the well- 

 known carbonic acid gas, properly called 

 carbon di-oxide, as it contains two parts 

 of oxygen. This is an acid oxide, com- 



