STEPHEN HALES 133 



based upon a series of chemical experiments per- 

 formed by himself. Not being satisfied with what 

 he knew of the relation between "air" (by which he 

 meant gas) and the solid bodies in which he sup- 

 posed gases to be fixed, he delayed the publication 

 of Vegetable Staticks for some two years, and 

 carried out the series of observations which are 

 mentioned in his title-page as "An attempt to 

 analyse the air, by a great variety of chymio- 

 statical experiments," occupying 162 pages of his 

 book.^ 



The theme of his inquiry he takes {Vegetable 

 Staticks y p. 165) from "the illustrious Sir Isaac 

 Newton," who believed that "dense bodies by 

 fermentation rarify into several sorts of Air ; and 

 this Air by fermentation, and sometimes without it, 

 returns into dense bodies." 



Hales' method consisted in heating a variety 

 of substances, e.g. wheat-grains, pease, wood, hog's 

 blood, fallow-deer's horn, oyster-shells, red-lead, 

 gold, etc., and measuring the "air" given off from 

 them. He also tried the effect of acid on iron 

 filings, oyster-shells, etc. In the true spirit of 

 experiment he began by strongly heating his 

 retorts (one of which was a musket barrel) to make 

 sure that no air arose from them. It is not evident 

 to me why he continued at this subject so long. He 

 had no means of distinguishing one gas from 

 another, and almost the only quality noted is a 

 want of permanence, e.g. when the CO^ produced 



^ It appears that Mayow made similar experiments. Diet. 

 Nat. Biog. s.v. Mayow. 



