TUB 2<ITKIC AOIL) OF TUE SOIL. 259 



face charged with sulpliidcs (sulphur-springs). Water 

 contahiiiig sulpliiites in sohitiou often acquires an odor of 

 sulphuretted hydrogen by being kept bottled, the cork or 

 other organic matters deoxidizing the sulphates. The 

 earth just belo^v the {)aving-stones in Paris contains con- 

 siderable quantities of sulphides of iron and calcium, the 

 gypsum in the soil being reduced l)y organic matters. 

 (Chevreul.) These sulphides, when exposed to air, speed- 

 ily oxidize to sulphates, to suffer reduction again in con- 

 tact with the appropriate substances, and under certain 

 conditions, operate continuously, to gather and impart 

 oxygen. One of the causes of the often remarkable and 

 inexplicable effects of plaster of Paris when used as a fer- 

 tilizer may, perhaps, be traced to this power of oxidation, 

 resulting in the formation of nitrates. This j^oint requires 

 and is aa'cII worthy of special investigation. 



c. Lastly, the free nitrogen of the atmosphere appears 

 to be in some way involved in the act of nitrification — is 

 itself to a certain extent oxidized in the soil, as has been 

 maintained by Saussure, Gaultier de Claubry, and others 

 {Cynellii's Hand-book of Chemhtry^ II, 388). 



The truth of this view is sustained by some of Bous- 

 singault's researches on the garden soil of Liebfrauenberg. 

 {Aijrouomle, et<:, T., 1, SIH)!" On the 29th of July, 1858, 

 he spread out thinly 120 grammes of this soil in a shallow 

 glass dish, and for three months moistened it daily with 

 water exempt from compounds of nitrogen. At the end 

 of this time analysis of the soil showed that while a small 

 proportion of carbon (0.825° IJ had wasted by oxidation, 

 the quantity of nitrogen had slightly increased. The 

 gain of nitrogen was but 0.009 grm. = 0.008"| ^. 



In five other experiments where plants grew for several 

 months in small quantities of the same garden soil, either 

 in the free air but sheltered from rain and dew, or in a 

 confined space and watered with pure water, analyses 



