A HISTORY OF METABOLISM 15 



"compleat astonishment", he too might have had the honor reserved for 

 Lavoisier. 



Black (1728-1799) in 1754 published a Latin essay which, in its 

 English form, is entitled "Experiments on Magnesia Alba, Quicklime 

 and other Alkaline Substances." In this Black describes the discovery 

 of "fixed air" or carbonic acid. Black writes of himself as follows : 



In the early days of my chymical studies the author whose works made the 

 most agreeable impression on my mind was Markgraaf (1709-1782) of Berlin; he 

 contrived and executed his experiments with so much chymical skill that they 

 were uncommonly instructive and satisfactory; and he described them with so 

 much modesty and simplicity, avoiding entirely the parade of erudition and 

 self-importance, with which many other authors encumber their works, that I 

 was quite charmed with Markgraaf and said to Dr. Cullen that I would rather 

 be the author of Markgraaf s Essays than of all the chymical works in the library. 

 The celebrated Reaumur's method of writing appeared to me also uncommonly 

 pleasing. After three years spent with Dr. Cullen I came to Edinburgh to finish 

 my education in medicine. Here I attended the lectures of Dr. Monroe, senior, 

 and the other medical professors until the summer of 1754 when I received the 

 degree of Doctor of Medicine and printed my inaugural dissertation, "De Humore 

 Acido a Cibis Orto, et Magnesia Alba." 



Black finds that the carbonates yield "fixed air" on ignition and that 

 caustic alkalis absorb the same air. Magnesia alba loses half its weight 

 when heated and gives off "fixed air" when treated with acids. Lime 

 water does not combine with ordinary air but does combine with "fixed 

 air." Black describes the new found kind of air as one "which is dis- 

 persed through the atmosphere either in the state of a very subtle powder, 

 or more probably in that of an elastic fluid. To this I have given the 

 name of fixed air, and perhaps very improperly; but I thought it better 

 to use a word already familiar in philosophy than to invent a new name, 

 before we are more fully acquainted with the nature and properties of 

 this substance." 



This was the pioneer discovery in the field long known as pneumatic 

 chemistry. "Fixed air" was produced in fermentation, in the combus- 

 tion of carbon, and was eliminated in the respiration. The next gas to 

 be discovered was hydrogen. 



Cavendish (1731-1810) was a nephew of the third Duke of Devon- 

 shire. He was a man of wealth and of extremely eccentric character. It 

 was he who discovered hydrogen in 1766 and gave it the name of "in- 

 flammable air." He considered hydrogen to be phlogiston. Later, in 

 1781, he found that when two volumes of "inflammable air" and one 

 volume of Priestley's "dephlpgisticated air" (oxygen) were united by an 

 electric spark the airs disappeared and water resulted. Cavendish con- 

 cluded that dephlogisticated air was water deprived of its phlogiston. 



The French have always claimed that Lavoisier was the first to dis- 



