ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 87 
to detect. The greatest proportion of nitric acid found in 
rain occurred in a slow-falling morning shower, (9th Octo- 
ber, 1857, at Liebfrauenberg), viz., 62 parts * in 10 million 
of water. In fog, on one occasion, (at Paris, 19th Dec., 
1857,) 101 parts to 10 million of water were observed. 
Knop found in rain-water, collected near Leipzig, in - 
July, 1862, 56 parts; in rain that fell during a thunder- 
storm, 98 parts in 10 million of water. 
Boussingault found in rain an average of 2 parts, in 
snow of 4 parts, of nitric acid to 10 million of water. 
Mr. Way, whose determinations of ammonia in the at- 
mospheric waters collected by Lawes and Gilbert, at 
Rothamstead, during the whole of the years 1855-6, have 
already been noticed, (p. 63,) likewise estimated the nitric 
acid in the same waters. He found the proportion of ni- 
tric acid to be, in 1855, 4 parts, in 1856 4} parts, to ae 
million of water. 
Bretschneider found at Ida-Marienhiitte, Prussia, for the 
year 1865-6 an average of 84 parts, for 1866-7 an average 
of 44 parts, of nitric acid in 10 million of water. At Regen- 
walde, Prussia, the average in 1865-6 was 25 parts, in 
1866-7, 22 parts. At Proskau, the average in 1864-5 was 
81 parts. At Kuschen, the average for 1864-5 was 6 
parts; in 1865-6,7; in 1866-7, 8 parts. At Dahme, in 
1865-6, the average was 12 parts. At Insterburg, Pincus 
and Réllig obtained in 1864-5, an average of 12 parts; in 
1865-6, an average of 16 parts of nitric acid in 10 million 
of water. The highest monthly average was 280 parts, 
at Lauersfort, July, 1864; and the lowest was nothing, 
April, 1865, at Ida-Marienhiitte. 
Quantity of Nitric Acid in Atmospheric Water.—The 
total quantity of nitric acid that could be collected in the 
rains, etc., at Rothamstead, amounted in 1855 to 2.98 lbs., 
and in 1856 to 2.80 lbs. per acre. 
* In all the quantitative statements here and elsewhere, anhydrous nitric acid, 
Nz O;, (O=16, formerly NOs, O=8) is to be understood. 
