24 



SCIENCE 



[N. S. Vol. XLIII. No. 1097 



owing to the presence of this nitrate in the 

 soil, the chlorides, sulphates of sodium and 

 potassium exert a solvent action on the or- 

 ganic matter. The potassium nitrate has a 

 decomposition, while the solvent action of the 

 more pronounced solvent action on the 

 organic matter, which is intensified by double 

 carbonates of sodium and potassiimi are un- 

 doubtedly intensified by the hydrolyzation and 

 consequent production of caustic alkali. The 

 salts of calcium exert a repressive action be- 

 cause of the double decomposition and the 

 imion of the calcium to formed insoluble cal- 

 cium salts of the colored organic acids present 

 as already explained. In the presence of old 

 organic material such as occurs in the coal- 

 bearing shale the humifying action of either 

 the carhonates or other salts is entirely neg- 

 ligible but it undoubtedly is true that the 

 humifying action upon fresh organic matter 

 of the caustic soda produced by the hydroly- 

 zation of the sodiutm carbonate is an impor- 

 tant factor in the production of the black 

 color of the black alkali spots of alkali soils. 



Furthermore, the solvent action of potas- 

 sium nitrate on old organic matter may be 

 observed in the extraction of peaty soils in 

 the determination of acidity of the soil by the 

 Hopkins method. The potassium nitrate ex- 

 tract of peaty soils in this determination is 

 always colored, due to dissolved organic ma- 

 terial. The intensity of the color frequently 

 is so great as to give considerable trouble in 

 the subsequent titration of the extract with 

 an alkali, because the change in color of the 

 indicator can not be observed. The solubility 

 of the old organic matter of peaty soils in 

 potassium nitrate is certainly entirely anal- 

 ogous to the solubility of the old organic mat- 

 ter in the coal-bearing shales and sandstones 

 which constitute the parent material out of 

 which the soils of the " niter " areas are 

 formed. 



The color thus can be readily accounted for 

 without the instrumentality of the bacteria, 

 while, moreover, artificial niter spots may be 

 produced in the laboratory on a small scale 

 under conditions which preclude the presence 

 of any bacterial life whatever. Three hun- 



dred grams of a greenhouse soil, rich in 

 hiunus, was placed in small evaporating 

 dishes and the dish filled with a 10-per-cent. 

 solution of sodium nitrate. The solution was 

 then allowed to slowly evaporate by the sun's 

 rays. When all the moisture had evaporated 

 there was produced characteristic niter spots 

 including the color, hard crust and the mealy 

 crystalline condition underneath the crust 

 due to the accumulation of the soluble salts. 

 These spots were likewise produced when the 

 nitrate ivas added in the solid form and the 

 moisture added with a saturated solution of 

 mercuric chloride or a 5 per cent, solution of 

 carbolic acid. Control samples of the same 

 soil, in the absence of the nitrate, with or 

 without the antiseptic, failed to produce either 

 the color or other indications of the niter 

 spots. It is evident, therefore, that the bac- 

 teria play no important role in either the pro- 

 duction of the nitrates or color of the " niter 

 spots " of certain western soils. 



In addition to the evidence already pub- 

 lished, a detailed paper dealing with the 

 problem as it aSects other soils than those 

 already discussed is being prepared and will 

 be published later elsewhere. 



Egbert Stewaet 

 University op Illinois 



William Peterson 

 Utah Agricultural College 



mottled limestones and their bearing 

 on the origin of dolomitei 



SEVERAt examples of limestone mottled with 

 dolomite have been described during the past 

 few years, but R. C. Wallace was the first to at- 

 tempt seriously to interpret their meaning. In 

 a very suggestive paper entitled " Pseudobrec- 

 ciation in Ordovician Limestones in Mani- 

 toba "- he points out that the dolomite patches 

 in these limestones foUow fucoid-like mark- 

 ings suggesting algas, and concludes that the 

 relationship has resulted from a process of 

 local replacement produced by the magnesia 

 contained in algae which were imbedded in the 



1 With the permission of tbe director of the 

 Iowa Geological Survey. 



2 Jour. Geol., Vol. XXI., 1913, pp. 402^21. 



