226 Royal Institution. 



of the physiology of vegetables, and strikingly displayed some 

 of those masterly and beneficent adjustments of nature by which 

 the different members of the creation are made to minister to 

 each other's wants, and thus preserve that eternal harmony 

 which marks the natural world." 



Mr. Brande said it was a curious fact that some plants effected 

 the same changes upon tlie atmosphere as animals, only in a 

 much less degree : he alluded to some experiments of his own, 

 in which similar portions of contaminated air Avere exposed to 

 the operation of the vine, mint, the pea, and water cresses, all 

 in a healthy state of vegetation : by the vine and mint it was 

 purified, unaltered by the pea, and rendered less pure bv the 

 cresses. Mr. Brande hoped upon these grounds to be able to 

 explain some discordant results of later experimentalists. 



The remainder of the lecture was occupied with the details of 

 Dr. Priestley's greatest discovery, that of dephlogisticated air, 

 or, as it has since been styled, oxygen gas, on the first of Au- 

 gust, 1774. 



In his sixth lecture Mr. Brande resumed the history of Dr. 

 Priestley's researches. Foiled in his attempts to collect and 

 preserve certain gases over water, Dr. Priestley devised the ex- 

 pedient of confining them over quicksilver. It was thus that he 

 obtained muriatic acid, sulphurous acid, and the volatile alkali, 

 in their pure elastic form : he then imagined, that by mixing the 

 acid and alkaline air he should obtain a neutral aeriform fluid ; 

 but to his surprise a solid salt resulted, and the gases were 

 wholly condensed. Having illustrated these and some other in- 

 quiries of minor importance, by simple but satisfactory experi- 

 ments, the professor took a general view of Dr. Priestley's 

 scientific c^iaracter and discoveries. 



Mr. Brande next proceeded to illustrate the discoveries of 

 Scheele ; he dwelt principally upon that of dephlogisticated mu- 

 riatic acid, a subject that has given rise to a very singular con- 

 troversy in the chemical world. Scheele regarded it as an ele- 

 mentary substance, as the base of muriatic acid : it was next 

 examined by Berthollet, who imagined that it contained oxygen, 

 and was composed of that principle united to muriatic acid. 

 Sir H. Daw had found reason to doubt the accuracy of these 

 conclusions, which for twenty years had prevailed in the chemi- 

 cal world, and by a series of satisfactory inquiries had re-esta- 

 blished the correctness of Scheele's original views. Mr. Brande 

 said, that any extended discussion upon this subject would be 

 misplaced in his present lecture ; but it had been alluded to in a 

 manner neither complaisant nor philosophical, in a recent French 

 publication — and whenever the claims of his eminent predecessor 

 were unwarrantably attacked and infringed, it became his impe- 

 rious duty to step forward in their defence. 



Some 



