SECT. XXVIII. METALLIC OXIDES. 473 



several plants, but never except in very small 

 quantities. 



SECTION XXVIII. 

 Metallic Oxides. 

 AMONG the substances found in the ashes of vege- Occur in 



r small 



tables we must class also metals. I hey occur quantities, 

 however only in small quantities, and are not 

 to be detected except by the most delicate experi- 

 ments. 



The metals hitherto discovered in plants are iron, 

 manganese, and perhaps gold. Of these iron is by 

 far the most common. It occurs in the state of an 

 oxide, and the ashes of hard and woody plants, such 

 as the Oak, are said to contain nearly -J^ part of 

 their own weight of this oxide.* The ashes of 

 salsola contain also a considerable quantity. 



The oxide of manganese was first detected in the 

 ashes of vegetables by Scheele, and afterwards 

 found by Proust in the ashes of the Pine, Calen- 

 dula) Vine, Green Oak, and Fig-tree.^ 



Beccher, Kunckel, and Sage, together with some 

 other chemists, contend also for the existence of 

 gold in the ashes of certain plants ; but the very 

 minute portion which they found seems more likely 

 to have proceeded from the lead employed in the 

 process than from the ashes of the plant. 



* Fourcroy, vol. viii. p. 203. 

 t Thomson's Chemistry, vol. iv. p. 357. 

 8 



