Mr. A, Gages on Vivianile. 185 



of decay, which in moist earth is necessarily very slow, carbonic 

 acid, marsh-gas, hydrogen, and sulphide of hydrogen are evolved. 

 In the presence of such gases, any sesquioxide of iron present 

 would be reduced to the state of protoxide ; in this state the 

 carbonic acid evolved by the decomposing bone or surrounding 

 organic matter is sufBcieut to dissolve it, as well as phosphate of 

 lime, which under such circumstances would be rapidly taken up, 

 as the experiments of Moride and Bobierre have fully established. 

 Double decomposition would of course ensue between two such 

 solutions, with a formation of phosphate of protoxide of iron. 



As plants contain a certain amount of phosphoric acid, and as 

 during their decay the same favourable conditions for the reduc- 

 tion of the sesquioxide of iron exist as in the decay of bones, 

 Vivianite may be formed wherever vegetable matter decays in the 

 presence of compounds of iron. For example, the ashes of peat 

 often contain as much as 3 per cent, of phosphate (part being 

 sometimes phosphate of iron) ; and consequently peaty soils or 

 turf moors may be expected to present the conditions essential 

 to the formation of blue iron earth. It has accordingly been 

 found in many bogs in almost every county of Ireland. 



The specimen of iron earth which I desire at present to con- 

 sider, presents an excellent example of this kind of reducing 

 action. This specimen was obtained from the margin of the 

 bog of Allen ; the blue phosphate is disseminated through a mass 

 of clay and sand mixed with peat, or rather what appears to be 

 carbonized peat. 



The clay itself exhibits traces of combustion, and it appears to 

 be slightly baked here and there ; it very probably formed part 

 of a peaty soil burned for the purpose of reclaiming the land. 



The remains of the plants usually found in peat are observable, 

 such as si)ecies of Sphagnum, hazel-nuts. Erica; a stem of the 

 last-named plant in a perfectly carbonized state, and also some 

 hazel-nuts, are covered over with the blue iron earth. 



The question naturally suggests itself, whether the action of 

 fire would have had anything to do with the production of the 

 blue phosphate ? There can be no doubt that blue phosphatic 

 compounds may be formed at a high heat. 



If phosphate of magnesia, or lime containing traces of iron 

 and intimately mixed with organic matter, be submitted to a 

 strong heat, it frequently acquires a sky-blue colour, evidently 

 due to the formation of a phosphate of iron. This blue colour 

 may often be seen when phosphate of ammonia and magnesia 

 is burned in a filter containing traces of iron : a slight trace of 

 carbonic acid is evolved on moistening the phosphate with an 

 arid, indicating that some of it has been decomposed. 



Kvrii if wc admit that V^ivianite contains sesquioxide of iron, 



