DISCOVERIES IX THE CELESTIAL SPACES 729 



teenth century, regarding the meteorological process. Van 

 Helmont was not acquainted with the simple method of taking 

 up and separating his gas sylvestrc, (the name under which he 

 comprehended all un-inflammable gases, which do not main- 

 tain combustion and respiration, and differ from pure atmos- 

 pheric air ; ) but he caused a light to burn in. a vessel under 

 water, and observed that when the flame was extinguished the 

 water entered, and the volume of air diminished. Van 

 Helmont likewise endeavoured to show by determinations- 

 of weight, (which we find already given by Cardanus), that 

 all the solid portions of plants are formed from water. 



The alchemistic opinions of the middle ages regarding the 

 composition of metals, and the loss of their brilliancy by com- 

 bustion in the open air, (incineration, calcination) led to a desire 

 of investigating the conditions by which this process was at- 

 tended, and the changes experienced by the calcined metals,, 

 and by the air in contact with them. Cardanus, as early 

 as in 1553, had noticed the increase of weight that accom- 

 panies the oxidation of lead, and perfectly in accordance 

 with the idea of the myth of Phlogiston, had attributed it to the 

 escape of a "celestial fiery matter," causing levity; and it was- 

 not until eighty years afterwards that Jean Rey, a remarkably 

 skilful experimenter at Bergerac, who had investigated with 

 the greatest care the increase of weight during the calci- 

 nation of lead, tin, and antimony, arrived at the important 

 conclusion that this increase of weight must be ascribed ta 

 the access of the air to the metallic calx. " Je responds et 

 soutiens glorieusement," he says, "que ce surcroit de poids- 

 vient de 1'air qui dans levase a ete espessi."* 



* Rey, strictly speaking, only mentions the access of air to the oxides; 

 he did not know that the oxides themselves (which were then called the 

 earthy metals,) are only combinations of metals and air. According to 

 him, the air makes "the metallic calx heavier, as sand increases in weight 

 when water hangs about it." The calx is susceptible of being saturated 

 with air. " L'air espaissi s'attache a la chaux, ainsi le poids augmente du 

 commencement jusqu'it la fin: mais quand tout en est affubJe, elle n'en 

 sauroit prendre d'avantage. Ne continuez plus votre calcination soubs 

 cet espoir, vous perdriez vostre peine." lley's work thus contains the 

 first approach to the better explanation of a phenomenon, whose more 

 complete understanding subsequently exercised a favourable influence in. 

 reforming the whole of chemistry. See Kopp, Gesch. der Chemie, Th. iii. 



