KARL WILHELM SCHEELE 123 



matter in order to obtain a clear conception of it. One may reason- 

 ably be amazed at the ideas and conjectures which authors have 

 recorded on the subject, especially when they give a decision re- 

 specting the phenomenon of fire; and this very matter was of the 

 greatest importance to me. I perceived the necessity of a knowledge 

 of fire, because without this it is not possible to make any experiment ; 

 and without fire and heat it is not possible to make use of the action 

 of any solvent. I began accordingly to put aside all explanations of 

 fire ; I undertook a multitude of experiments in order to fathom this 

 beautiful phenomenon as fully as possible. I soon found, however, 

 that one could not form any true judgment regarding the phe- 

 nomena which fire presents, without a knowledge of the air. I saw, 

 after carrying out a series of experiments, that air really enters into 

 the mixture of fire, and with it forms a constituent of flame and of 

 sparks. I learned accordingly that a treatise like this, on fire, could 

 not be drawn up with proper completeness without taking the air 

 also into consideration. 



4. Air is that fluid invisible substance which we continually breathe, 

 which surrounds the whole surface of the earth, is very elastic, and 

 possesses weight. It is always filled with an astonishing quantity 

 of all kinds of exhalations, which are so finely subdivided in it that 

 they are scarcely visible even in the sun's rays. Water vapours 

 always have the preponderance amongst these foreign particles. The 

 air, however, is also mixed with another elastic substance resembling 

 air, which differs from it in numerous properties, and is, with good 

 reason, called aerial acid by Professor Bergman. It owes its pres- 

 ence to organised bodies, destroyed by putrefaction or combustion. 



5. Nothing has given philosophers more trouble for some years 

 than just this delicate acid or so-called fixed air. Indeed it is not 

 surprising that the conclusions which one draws from the properties 

 of this elastic acid are not favourable to all who are prejudiced by 

 previously conceived opinions. These defenders of the Paracelsian 

 doctrine believe that the air is in itself unalterable; and, with Hales, 

 that it really unites with substances thereby losing its elasticity ; but 

 that it regains its original nature as soon as it is driven out of these 

 by fire or fermentation. But since they see that the air so produced 

 is endowed with properties quite different from common air, they 

 conclude, without experimental proofs, that this air has united with 



