AGRICULTURAL CHEMISTRY AND GEOLOGY. 177 



Messrs. Lawes and Gilbert deduced from their experiments that turnips require more 

 phosphoric acid in the soil than wheat, because that, on what they considered an exhausted 

 soil, the addition of superphosphate of lime enabled them to raise turnips. Prof. Liebig, in 

 his new work, has objected to this that the soil was not exhausted, as is proved by the fact 

 that it yielded tolerable crops of wheat ; and expresses his belief that the yield of turnips 

 was not due to the supply of phosphoric acid, but to the solvent action exercised on the 

 silicates of the soil by the free sulphuric acid of the agricultural superphosphate which was 

 applied in large quantities. The considerations contained in the above note explain why 

 wheat requires a soil richer in phosphoric acid than the turnip does. 



It is an interesting fact that a soil does exist which produces wheat, but refuses entirely 

 to grow turnips, as the experimental soil of Messrs. Lawes and Gilbert. In the majority of 

 cases we should expect the reverse. This shows the danger of too hasty generalization, and 

 the importance of having a thorough knowledge of all the circumstances which act in any 

 particular case. 



On the Amounts of Ammonia and Nitric Acid in Rain Water. 



At the British Association, Dr. Gilbert and Mr. Lawes communicated the results of their 

 investigations on the amounts of ammonia and nitric acid in rain water. Their results during 

 many months of the last two years were tabulated and compared with those of Boussingault ; 

 the great result being that rain water contains not quite one part of nitrogen to the million 

 in the form of ammonia, and about five parts to the million in that of nitric acid. The 

 ammonia is found in largest quantity in mists and dews, as might naturally be expected from 

 its being evolved at the surface of the earth, and being absorbed by any moisture. In answer 

 to questions put to him afterwards, Dr. Gilbert stated that the nitric acid was found most 

 abundantly after storms, and varied very greatly at different periods of the year. The amount 

 of ammonia which descended in a month's rain was more constant. The doctor expressed his 

 opinion, but with hesitation, that nitric acid and ammonia were about equally efficient in 

 supplying nitrogen for plants ; and therefore, as nitric acid is the more abundant in the atmo- 

 sphere, he conceived that it afforded actually the larger quantity of azote to the vegetable world. 



Bovissingault has recently published some additional researches on the above subject, from 

 which it appears that the rain of the country contains less ammonia than that of the city, and 

 that the ammonia is more abundant at the beginning than at the end of a shower. He has 

 also examined the dew, and always found it to contain ammonia. The proportions by several 

 trials were six milligrammes to the litre ; but the amount is reduced to 1 -02 after a rainy 

 day. On the 14th to the 16th of November, a thick mist prevailed so rich in ammonia that 

 the water had an alkaline reaction ; a litre of the water contained about two decigrammes of 

 carbonate of ammonia. Seventy-five rains, including the dew and mist examined, contained 

 as a mean half a milligramme of ammonia. The great quantity of ammonia contained in the 

 mist appears interesting in its bearing on vegetable pathology ; in fact, although ammonia in 

 small quantity is favorable to vegetation, a large proportion would be injurious, and would 

 show its effects, especially on the leaves of flowers. Moreover, such a storm might have a 

 deleterious influence upon respiration, and especially on the lungs of persons with pulmonary 

 affections. 



New Theories in Agricultural Science. 



M. Baudkimont, professor of chemistry at the Faculty of Sciences at Bordeaux, has pub- 

 lished a work "On the Existence of Interstitial Currents in Arable Soil, and the influence 

 which they exert on Agriculture," in which, after a long study of the subject, he states that 

 there is a natural process at work by which liquid currents rise to the surface from a certain 

 depth in the ground, and thus bring up materials that help either to maintain its fertility or 

 to modify its character. Many phenomena of agriculture and of vegetation have at different 

 times been observed, which, hitherto inexplicable, are readily explained on this theory. 

 Such, for example, the improvements which take place in fallows ; and there is reason to 

 believe that these currents materially influence the rotation of crops. 



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