344 MEMOIR ON THE ORIGIN OF NITRE. 
I collected, in the country, at different places and at dif- 
ferent seasons, a great number of plants, those which are 
most commonly known. Some of them, collected from the 
species which ordinarily contain nitre, such as borage and 
the sun-flower, had been sown expressly in difficultly acces- 
sible places, and in soils which gave no appearance of nitre. 
But for still greater certainty, the same species were also cul- 
tivated under a glass case, in an artificial soil composed of 
coarse lime, stone in powder, washed with distilled water, 
and to which I had added as manure, powdered sheep’s 
bones, or a manure composed of human urine, fermented for 
a very long time with horse-dung, and not containing the 
least portion of nitre. Distilled water was always used for 
watering, and the most minute precautions were taken for 
isolating the pots which contained the plants, and to guard 
against the nitre which might come from without. 
The experiments which I made for proving the presence 
of nitre in these plants, have shown me that plants which 
grow near dwellings, on the sides of roads, and in all other 
places frequented by animals, ordinarily contain nitre ; but 
that we do not find it, on the contrary, in those which grow 
in the fields, in places inaccessible to animals, or in an artifi- 
cial soil perfectly free from nitre ; that, moreover, in these 
last conditions, plants which ordinarily contain nitre, such as 
borage, the sunflower, and pellitory, appear to vegetate only 
with difficulty; that their seeds do not always spring up, 
and that when they produce plants, the latter are so poor 
that borage, for example, scarcely attains the height of ten 
centimetres (about four inches) and the sunflower not more 
than double the height. 
The natural conclusion from these results was, that vege- 
tables have not the power of forming nitre, but that what 
they contain they derive from animals. 1 thus found myself 
in a circle, out of which I long despaired to find a way ; 
however, I did not lose courage. I recommenced the 
attempts I had made a hundred times, to effect the oxida- 
tion of the nitrogen of the urine ; I continued also to collect 
new observations on the cause of the nitrization of plants. 
I had to wait long for success ; but in the end I made an 
observation which gave me a clue to the solution of this 
difficulty ; I perceived that the sunflower, which, when cul- 
tivated in the open fields grew only with difficulty, and did 
not give nitre, grew, on the contrary, with the greatest 
facility and contained a considerable proportion of this salt, 
when cultivated in a garden. The cause of this difference 
could not be in the presence of manures, since these are sup- 
