156 EXPERIMENTS WITH FLUORIDE OF CALCIUM. 



4. In comparison with muriatic acid, and carbonate of 

 magnesia, each applied alone, with the view of inquiring 

 whether the effect it produces, if any, is due to the magnesia, 

 or to the chlorine it contains, or is caused by some special pro- 

 perty which the chloride as a compound possesses. Its great 

 solubility is such a property ; and it is not unlikely that this 

 will alone cause its magnesia to act in the soil, and upon the 

 plant, in a very different way from the nearly insoluble carbo- 

 nate. 



4. Suggestions for experiments with the fluoride of calcium , 

 (fluor spar.} 



Fluorine, or fluoride of calcium, has not been much sought 

 for as yet in the ashes of plants, but it must exist there, since it 

 is found in the proportion of from 2 to 4 per cent in the earthy 

 part of the bones and teeth of animals. As the mineral fluoride 

 can in some parts of the country be procured in considerable 

 quantities, it would be interesting, therefore, to make experi- 

 ments with it upon growing plants. Being very sparingly 

 soluble hi water, it may be applied with much safety. For 

 the same reason it ought perhaps to be laid on the land, or 

 around the seeds or roots of plants, in considerably larger doses 

 than any of the soluble saline substances of which we have 

 hitherto treated. It ought to be tried 



1. Alone, applied in different proportions and to different 

 plants. 



2. In comparison with an equivalent quantity of carbonate 

 of lime finely powdered chalk. This will show how far any 

 effect can be ascribed to the fluorine which the fluoride contains. 



3. In comparison with sulphate of lime common gypsum. 

 It cannot well be tried against the chloride of calcium, because 

 of the extreme solubility of the latter, and the greater ease 

 therefore with which, as we may presume, the roots of plants will 

 take it up. Indeed, it will be necessary first of all to know with 

 some degree of correctness, what effect, if any, the fluoride does 

 produce, before we can contrive further experiments by which 

 that effect is likely to be tested and analysed. 



