THE OPPORTUNITY OF THE AGRICULTURIST 691 



every cook know ? Why do we poke the fire — why is a chimney 

 provided to the fireplace ? We know that air must have access 

 to the kindled coal — that one function of the chimney is to cause 

 a draught ; every one knows the effect of so holding a news- 

 paper as to close the opening above the grate and force the air 

 to pass rapidly over the burning coal. Clearly the air is in some 

 way necessary and promotes the burning. Such an argument 

 as this would lead to an experiment being made to ascertain 

 what happens to the air when things burn in it and ultimately 

 to the discovery that air consists to the extent of about one-fifth 

 of a gas which has an extraordinary affection for all combustible 

 substances, just as water and the gas set free from limestone by 

 acids have for lime. When this constituent of air and a combus- 

 tible substance meet under appropriate conditions, they contract 

 a firm union with great display of warmth. The products of such 

 unions vary much in character, some being solid, some liquid, 

 some gaseous ; some few are neutral like water, some are 

 alkaline like lime and soda, whilst others are acid. The gas is 

 named Sour-stuff, because when the part which it plays in com- 

 bustion first came to be understood, the substances with which 

 the experiments were made happened to be such as gave rise to 

 acids. The Germans, who are direct, simple folk, call the gas to 

 the present day Sour-stuff— the stuff which makes sour things ; 

 so do we, without knowing it, as — following the lead of the 

 French — we use the Greek equivalent oxygen. But having so 

 long enjoyed the advantages of an exclusively classical educa- 

 tion, we no longer attempt to apply our knowledge and so use 

 the word without thought and without being reminded of its 

 significance. 



When coal or wood, indeed anything of vegetable or animal 

 origin, is burnt, it is seemingly destroyed — that it takes wings 

 to itself and dissolves into thin air is the discovery of but little 

 more than a century. The winged product we know is the gas 

 imprisoned in limestone, on this account called by Black — who 

 was the first to recognise its individuality — Fixed air, now known 

 in our technical jargon as Carbon Dioxide, the compound which 

 gives rise when joined to water to the very weak and unstable 

 acid, carbonic acid. To the instructed ear, these two names 

 carry oceans of meaning. If you know how the expression 

 dioxide is arrived at you are acquainted with the theoretical 

 basis — the molecular-atomic theory — on which chemistry rests. 



