138 



LECTURES ON 



Nitric acid, the well-known compound of nitrogen and oxygen, oc- 

 curs in the atmosphere in very minute quantity, usually in the form 

 of nitrate of ammonia, This body being incapable of existing in 

 vapor, and readily soluble in water, is brought to the earth in dews 

 and rains. Its quantity is even more minute than that of ammonia. 

 The most trustworthy estimations are those of Way, who found in the 

 waters that fell upon an acre at Rothamsteacl, in 1855, 2.98 pounds, 

 and in that of 1856, 2.80 pounds of nitric acid, or about one part of 

 nitric acid to two million parts of water. 



In the soil, nitric acid often occurs in considerable quantity, (the 

 result of chemical processes which we shall presently notice.) Here it 

 exists in combination with various bases, usually as nitrates of lime, 

 soda, and potash. The fertility of soils in which nitrates accumu- 

 late, and the remarkable effects of their application as fertilizers, are 

 evidence that nitric acid feeds vegetation. 



It is again to Boussingault 

 that we owe the more careful 

 study of its effects. Among 

 other experiments he made 

 the following : Two seeds 

 of Hdianthus argophyllus were 

 planted in each of three pots, 

 the soil of which, consisting 

 of a mixture of brick-dust and 

 8jj|sand, as well as the pots them- 

 selves, had been thoroughly 

 freed from all nitrogenous com- 

 pounds by ignition and washing 

 with distilled water. To the soil 

 of the pot A, fig. 10, nothing was 

 added save the two seeds, and 

 distilled water, with which all 

 the plants were watered from 

 time to time. With the soil of 

 pot C (fig. 1 2) were incorporated 

 small quantities of phosphate 

 of lime, of ashes of clover and 

 bicarbonate of potash, in or- 

 der that the plants growing 

 in it might have an abundant 

 supply of all the mineral mat- 

 ters they needed. Finally, the 

 soil of pot B, fig. 11, received 

 the same mineral matters as 

 pot C, and in addition, a small 

 quantity of nitric acid as ni- 

 trate of potash. The seeds 

 were sown on the 5th of July, and on the 30th September, the 

 plants had the relative size and appearance seen in the figures, re- 

 d uced to one-sixth of the natural dimensions. 



