180 Mr, Swainson o?t the Natural Affinities 



acid soon made its appearance, and then the gas became ca- 

 pable of impregnating chalk with nitrous acid as at first *." 



These experiments of Thouvenel, and particularly the last 

 observation, point out carbonic acid as the important agent in 

 nitrification, at least as distinctly as could be expected of ex- 

 periments of this nature. 



It has all along been observed in the management of artifi- 

 cial nitre-beds, that although free exposure to the atmosphere 

 be indispensable to the progress of nitrification, yet a strong 

 current of air is exceedingly prejudicial. The rapid circula- 

 tion of the atmosphere would be attended with the quick dis- 

 sipation of the carbonic acid gas, upon which we have sup- 

 posed the superiority of these nitre-beds to depend. 



The atmosphere at all times and places abounds hi carbonic 

 acid gas, as the exposure of lime-water would quickly indicate. 

 In those chalks and calcareous soils, in which the spontaneous 

 production of nitrous salts is observed, the activity of the car- 

 bonate of lime may, therefore, equally depend upon its disso- 

 lution, effected by the absorption of moisture and carbonic 

 acid from the atmosphere. It would still, however, be a cu- 

 rious subject of inquiry — whether these soils and chalks do 

 not, in some cases, contain within themselves the carbonic 

 acid necessary in conjunction with water to effect their partial 

 solution, and be thus enabled to act to a greater extent upon 

 the absorbed oxygen and azote — the elements of nitric acid ? 



Should this theory of the instrumentality of carbonic acid, 

 m nitrification, be eventually substantiated, several improve- 

 ments, in the artificial production of nitre, might evidently be 

 deduced from it. 



XXXVIII. ASketch of the Natural Affinities of thc'Le^\do\>ievsi 

 Diurna ofLatreille. By William Swainson, Esq. F.R.S. 

 F.L.S. 4-c.t 

 npO those who have traced the progress of human know- 

 -*- ledge, or are themselves engaged in its pursuit, it must 

 appear evident that its extent would have been much greater 

 than it really is, were we not so frequently withheld from com- 

 municating that which 'noe know, from a sense of the importance 

 of that which we do not hww. Hence it is, that undertakings 

 long meditated upon, and even cari'ied beyond the point to 

 which others have reached, are frequently laid aside on the 

 appearance of some unexpected difficulty or temporary em- 



* Aikins' Chemical Dictionary, vol. ii. 160. From Mem. Etrang. de 

 PAcad. des Sciences, torn. xi. 503. f Communicated by the Author. 



barrassment. 



