158 DR WILSON ON THE SOLUBILITY OF 



5. Of the presence of Fluorine in Plants. 



Comparatively few examinations of plants have yet been made, in reference 

 to the occurrence of fluorine in them ; but these, on the Avhole, have been satis- 

 factory. Sprengel appears to have been the first to suggest the likelihood of its 

 presence in vegetables, but failed in detecting it in any of them, and referred his 

 failure " to its existing in such a state of combination as caused it to be dissipated 

 by the heat necessary for expelling the carbonaceous matter, so that it could not 

 be detected in the ordinary method."* 



Dr Daubeny " ascertained that no sensible action is exerted on glass by heat- 

 ing, with sulphm-ic acid, the earthy phosphates present, in twelve pounds of 

 barley."}- I was equally unsuccessful with the ashes of Kanaster tobacco, and 

 of peas, and with those of charcoal and of coal. I ascribe the failure, however, 

 not to fluorine existing in a peculiar state of combination in plants, but to the 

 presence of silica, which, when in any quantity, makes the detection of fluorine 

 very difficult. I took no measures to separate the silica in the few experiments 

 I made on the subject, and Sprengel and Daubeny appear to have omitted the 

 same essential preliminary. Dr Will of Giessen, who kept this point cai-efully 

 in view, states that " careful experiments, conducted under his OAvn superin- 

 tendence, by Messrs James Mullek and Blake, severally, have shewn that the 

 ashes of French barley, grown in Switzerland, contain very distinct traces of it ; 

 both straw and grain Avere employed." % 



To Will the credit of first finding fluorine in plants is entirely due. As 

 barley, however, contains a large amount of calcareous phosphates, which the 

 fluoride of calcium has been supposed to accompany in a peculiar state of combi- 

 nation, I thought it well to examine the ashes of a plant containing little phos- 

 phate of lime, and which might be considered as having derived any fluorine it 

 contained directly from the water its roots absorbed. I chose for this purpose the 

 crudest American potashes, which, as they are obtained in part by burning the 

 young and succulent branches of trees, should contain portions of all that is soluble 

 in the sap. A pound Aveight of ashes was supersaturated with hydrochloric acid, 

 the liquid poured off, neutralised with ammonia, and precipitated by nitrate of 

 baryta. The precipitate washed and dried, when treated with Nordhausen 

 sulphuric acid in a lead basin, in the way already described, etched glass dis- 

 tinctly. 



Whether the fluorine found in plants is essential to them, and serves some 

 purpose in their organization, or merely circulates in then* sap, as other soluble 

 matters do, without being appropriated by the living organism, cannot be deter- 



* Chemical Society's Memoirs, vol. ii., p. 103. t Ibid. % Ibid, p. 182. 



