284 PICARDY ASHES. 



than wood soot, and in a given bulk actually contains a larger quan 

 tity of matter ; secondly, I have found that, for equal weights, coal 

 soot contains the larger quantity of azote. 



Picardy ashes are prepared by the slow and imperfect combustion 

 of the pyritic turf which is dug up in the department of the Aisne 

 for the manufacture of sulphate of iron and of alum. This turf piled 

 up, heats, and finally takes fire ; the combustion continues for about 

 a month, abundance of sulphureous vapors being disengaged. The 

 residue is a gray ash, still containing a quantity of carbonaceous 

 matter, which is found very advantageous in the way of top-dress- 

 ing for meadows. It might be maintained that the utility of such 

 ashes depends solely on the sulphate of lime which they contain ; 

 but it is ascertained that they are much more active as manure than 

 this substance employed by itself; analysis, in fact, explains in some 

 degree the fertilizing powers of these ashes, by showing that they 

 contain more than \ per cent, of azote, to say nothing of the saline 

 matters of which vegetables are so greedy. It is extremely proba- 

 ble that during the slow incineration of the turf, there is a quantity 

 of sulphate of ammonia produced. 



The ashes which remain after the lixiviation of the pyritic and 

 aluminous lignites which are mined for the purpose of making green 

 vitriol, are analogous to Picardy ashes, and are employed with equal 

 success ill agriculture. At Forges-les-Eaux, the pyritic earths after 

 .ixiviation are mixed with a quarter of their weight of turf ashes, 

 and form an active manure which is employed very extensively in 

 the country around the town of Bray in France : it is equally adapt- 

 ed to meadows and to land under roots, such as potatoes or turnips, 

 green crops or corn. Analysis shows these ashes to have the fol- 

 owing composition : 



SnhiMe organic ni.'ittcr 2.7 



Insolulilc humus 49.8 



Sulphato of protoxide and of peroxide of iron 1.8 



V\nv sand 39.0 



Sulphurct of iron > g« 



Peroxide of iron J 



100.0 



The vitriolic ashes of Forges-les-Eaux are more highly azotized 

 than those of Picardy ; they contain 'J.7*J per cent, of azote. 



The effect of the imperfect combustion of these pyritic turfs, the 

 product which results from it, explains to a certain extent the bene- 

 ficial effects of the practice o( paring and burnim^, an important and 

 widely spread practice, the utility of which it would be ditlicult to 

 understand, were it not connected in some way with the production 

 of ammoniacal ashes. 



The useful effects of paring and burning, are, in all probability, 

 connected with the destruction of organic matter, very poor in azo- 

 tized principles ; in the transforn)ation of the surface of the soil into 

 1 porous, carbonaceous earth, made apt to condense and retain the 

 ammoniacal vapors disengaged during the combustion ; lastly, by 

 the production of alkaline and earthy salts, which are familiarly 

 known to exert a most beneficial intluence uj)on vegetation. These 



