134 STEPHEN HALES 



was dissolved by the water over which he collected 

 it. Sir E. Thorpe^ points out that Hales must have 

 prepared hydrogen, carbonic acid, carbonic oxide, 

 sulphur dioxide, and marsh gas. It may, I think, 

 be said that Hales deserved the title usually given 

 to Priestley, viz. "the father of pneumatic^ chemis- 

 try." 



Perhaps the most interesting experiment made 

 by Hales is the heating of minium (red-lead) with 

 the production of oxygen. It proves that he knew, 

 as Boyle, Hooke and Mayow did before him, that 

 a body gains weight in oxidation. Thus Hales 

 remarks : "That the sulphurous and aereal particles 

 of the fire are lodged in many of those bodies which 

 it acts upon, and thereby considerably augments 

 their weight, is very evident in Minium or Red Lead, 

 which is observed to increase in weight in under- 

 going the action of the fire. The acquired redness 

 of the Minium indicating the addition of plenty of 

 sulphur in the operation." He also speaks of 

 the gas distilled from minium, and remarks : 

 "It was doubtless this quantity of air in the 

 Minium which burst the hermetically sealed 

 glasses of the excellent Mr. Boyle, when he 

 heated the Minium contained in them by a 

 burning glass" (p. 287). 



This was the method also used by Priestley in 

 his celebrated experiment of heating red-lead in 

 hydrogen, whereby the metallic lead reappears 



* History of Chemistry, 1909, i. p. 69. 



* Hales made use of a rough pneumatic trough, the invention 

 of which is usually ascribed to ftiestley (Thorpe's History of Chemis- 

 try. I. p. 79). 



