to HOW CROPS FEED. 



When the combustion is so perfect that the resulting wa- 

 ter is colorless and pure, only nitrous acid is formed ; 

 when, on the other hand, a trace of organic matters es- 

 capes oxidation, less or no nitrous acid, but in its place 

 ammonia, appears in the water, and this under circum- 

 stances that preclude its absorption from the atmosphere. 



Zabelin gives no proof that the combustibles he etn<> 

 ployed were absolutely free from compounds of nitrogen, 

 but otherwise, his experiments are not open to criticism. 



Meissner's observations were indeed made under some- 

 what different conditions ; but his negative results were 

 not improbably arrived at simply because he employed a 

 much less delicate test for nitrous acid than was used by 

 Schonbein, Boettger, Jones, and Zabelin.* 



We must conclude, then, that nitrous acid and ammonia 

 are usually formed from atmospheric nitrogen during rap- 

 id combustion of hydrogen and compounds of hydrogen 

 and carbon. The quantity of these bodies thus generated 

 is, however, in general so extremely small as to require the 

 most sensitive reagents for their detection. 



At low te?nperat((res. — Schonbein was the first to observe 

 that nitric acid may be formed at moderately elevated or 

 even ordinary temperatures. He obtained several grams 

 of nitrate of potash by adding carbonate of potash to the 

 liquid resulting from the slow oxidation of phosphorus in 

 the preparation of ozone. 



More recently he believed to have discovered that ni- 

 trogen compounds are formed by the simple evaporation 

 of water. He heated a vessel (which was indifferently of 



* Meissner rejected Price's test in the belief that it cannot serve todistinjuish 

 nitrous acid from peroxide of hydrogen, H2 O2. He therefore made the liquid 

 to be examined alkaline with a slight excess of potash, concentrated to small 

 bulk and tested with dilute sulphuric acid and protosulphate of iron. {Uniers. 

 u. d. Swiers'off, p. 233). Scliiinboin had found that iodide of potassium is decom- 

 posed after a little time by concentrated sohitions of peroxides of hydrogen, but in 

 unaff.'Ctcd by this body when dilute. {Jour, fur prakt. Chum., Ixsxvi, p. !)()). 

 Zabelin agrees with Schonbein that Price's test is decisive between peroxide ol 

 hydrogen and nitrous acid. {Ann. CItcin. u. Ph., cxsx, p. 5S.) 



