250 THEORY OF THE FORMATION Of NITRIC ACID. 



of common earth, of calcareous sand or marl, and of wood-ashes. 

 This heap is watered with the urine of herbivorous animals, and the 

 mixture is stirred or shifted from time to time to favor the access 

 of the air ; and with the same view, the workmen are very careful 

 never to beat or press the heap, which is generally from two to two 

 and a half feet in thickness, and usually of the whole length of the 

 hut or shed. Experience has shown that the process of nitrification 

 goes on best in the shade. In Prussia, the practice is to wet vi'ith 

 the water of a dunghill a mixture composed of five parts of vegeta- 

 ble earth, and one part of wood-ashes and straw. With this kind 

 of mortar, solid walls or masses from twenty to four and twenty 

 feet in length, by about six feet and a half in thickness, are built, 

 rods of wood being introduced during the construction in eonsidera- 

 ole numbers, and in such a way that they can be pulled out w^hen 

 the mass has acquired sufficient solidity ; by this means it is obvious 

 that a very free access of air is secured to the interior of these 

 litre walls, which are always built in damp places, and thatched over 

 with straw to preserve them both from the sun and the rain. The 

 mass is watered from time to time, and after the lapse of a year, 

 '.he materials are held sufficiently impregnated with saltpetre to be 

 ivorth lixiviating. 



In these artificial nitre-beds we perceive the object to be, to com- 

 )ine the circumstances under which the nitrates are formed in the 

 oil of stables, and in the cellars of human habitations. Organic 

 A latters, rich in azote, are, in fact, brought into contact with earthy 

 . kaline carbonates. The necessity that is felt in the arrangement 

 c * nitre-beus for the introduction of substances of animal origin, 

 L \ds us to presume that the greater part of the nitric acid which is 

 pioduced, is derived from the azote of these substances. But 

 whether tliis azote combines with the oxygen of the air, or with the 

 oy.ygen of the organic principles, we do not know — we are still ig- 

 norant of the way in which the acidification is effected. 



Professor Liebig, setting out from the fact that azotized organic 

 substances always produce ammonia during their putrefaction, and 

 next perceiving that during the combustion of ammoniacal gas, 

 mixed with a large excess of hydrogen, there is always oxidation of 

 the azote, concludes that nitrification is the result of the slow com- 

 bustion of the ammonia which is the product of the azotized matters 

 in progress of decomposition. The azote of ammonia is indeed 

 oxidated under favor of divers conditions which it is easy to secure. 

 In burning animal substances by means of oxide of copper, it is well 

 known how many precautions must be taken to prevent the appear- 

 ance of nitrous acid ; and on the contrary, by taking measures to 

 favor th.>, production of this acid, for example, by passing a current 

 of ammoniacal gas over peroxide of iron or manganese in a red hot 

 tube, abund.ince of nitrate of ammonia is obtained. The same re- 

 sult follows exposure of a mixture of oxygen and ammoniacal gas 

 to the action of incandescent spongy platinum. The determining 

 cause of the acidification of the azote, which forms an element of 

 the ammonia, is probably due to this, that during the combustion two 



