RETROSPECT. 



(poitdrette), lose, at 230°, half of all the nitrogen contained in 

 them, in the form of carbonate of ammonia. Common stable ma- 

 nure, which contains 79 — 80 per cent, of water, must lose, when 

 heated to 230° in vacuo, at least three times as much nitrogen 

 as it retains ; that is, 3-4ths of all the nitrogen originally present 

 in it. But if we estimate it at haif of the quantity present in the 

 dried excrements, then the field must have received, in sixteen 

 years, 1950 lbs. of nitrogen. 



But in sixteen years, 1517 lbs. of nitrogen only were ob- 

 tained, IN THE FORM OF CORN, STRAW, AND TUBERS J much less, 



therefore, than the quantity furnished to the field. Hence his 

 erroneous conclusion, that the Legurninosae alone possess the 

 power of condensing nitrogen from the air ; and that it is neces- 

 sary to furnish nitrogen to the Graminese, and to plants such as 

 turnips and potatoes. But in the same time, and upon the same 

 surface of a good meadow, not receiving nitrogen, we may obtain 

 (on 1 hectare) 2060 lbs. of this element. 



It is well known that dried excrements form the principal fuel 

 in Egypt, where wood is scarce. For centuries the sal ammo- 

 niac used in Europe was supplied from the soot of these excre- 

 ments, until Gravenhorst, in the latter part of last century, 

 discovered how to prepare it, and instituted a manufactory at 

 Brunswick. 



The fields in the valley of the Nile receive no manure of ani- 

 mal origin except the fixed ingredients (which contain no nitro- 

 gen) of the ashes of the burnt dung ; and yet these fields have 

 been so fertile, for periods long before our history commences, 

 that this fertility has become a proverb, and is quite as remarkable 

 at the present day as it was in former times. These fields be- 

 come renovated by the mud deposited during the inundations of 

 the Nile ; the mineral ingredients of the soil removed in the crops 

 are thus restored to it. The mud of the Nile contains as little 

 nitrogen as the mud from the Alps, in Switzerland, deposited on, 

 and fertilizing our own fields by the inundations of the Rhine. 



Jn fact, if the mud of the Nile fertilizes the soil, in consequence 

 of its containing nitrogen, we must suppose immense strata of 

 nitrogenized animal and vegetable matter to exist in the mountains 

 of the interior of Africa, at heights above the line of perpetual 



