256 THE CANADIAN NATURALIST. [Sept. 



By means of sulphurous acid, also, in a state of aqueous 

 solution, apatite may be dissolved to the extent of about 

 TsW parts, under the above conditions ; but this last reaction 

 has not such an important bearing upon the theory of agri- 

 culture as those already described. 



The researches of Thenard, upon the action of clays on 

 phosphate of lime in carbonic-acid solution, show that 

 insoluble phosphate of alumina is formed, whilst the solution 

 contains all the lime, as carbonate* ; but, as the alumina in 

 clays is not in the free state, an acid silicate of alumina is 

 probably at the same time produced. 



Thenard also stated (loc. cit.^ that, by the action of an 

 aqueous solution of silicate of lime upon phosjohate of alumina, 

 silicate of alumina is precipitated, Avhilst tribasic phosphate of 

 lime (separable by means of carbonic acid) is also produced. 

 By repeating Th^nard^s experiment, a solution was obtained, 

 containing .011 gm. of lime sihcate to the litre of water, 

 which was completely decomposed in the manner indicated 

 by Thenard, by long boiling with pure artificial phosphate of 

 alumina, or with the clay previously used, Avhich contains 

 some phosphoric acid. Since, however, heat is requisite to 

 the success of this reaction, it is more probable that, in 

 nature, double silicates of alkalies with lime or magnesia, play 

 the part here assigned to solution of simple sihcate of lime. 



Deherain f asserts that the reverse of this reaction results 

 between phosphate of sesqui-oxyd of iron and carbonate of 

 lime: and it is probable that the surrounding conditions, as 

 to temperature, relative amounts, and mechanical division, 

 determine the nature of the resulting change. This was notably 

 the case in Eichhorn's remarkable experiments upon the 

 solubility of chabazite and natrolite in various saline solutions; 

 and, on the whole, it would seem that the numerous known 

 instances of departure from a regular order of affinities in 

 such reactions tend to show that the relations of many bodies, 

 with regard to their mutual affinities, are disposed to vary in 



*■ Compt. Kend. de I'Acad. des Sciences, Feb. 1, 1868. 

 t Quoted by Johnson, in the paper previously cited. 



