' 
THE NITRIC ACID OF THE SOIL. 253 
yellow or reddish color. When pure, it is white or color- 
less. From the shape of the crystals it has been called 
cubic * niter; it is also known as Chili saltpeter, having 
been formerly exported from Chilian ports, and is some- 
times termed soda-saltpeter. In 1854, about 40,000 tons 
were shipped from the port of Iquique. 
Nitrate of soda is hygroscopic, and in damp air be- 
comes quite moist, or even deliquesces, and hence is not 
suited for making gunpowder. It is easily procured arti- 
ficially by dissolving carbonate of soda in nitric acid. 
This salt is largely employed as a fertilizer, and for pre- 
paring nitrate of potash and nitric acid. 
Nitrate of Lime (Ca2NO,) may be obtained as a white 
mass or as six-sided crystals by dissolving lime in nitric 
acid anil evaporating the solution. It absorbs water from 
the air and runs to a liquid. Its taste is bitter and sharp. 
Nitrate of lime exists in well-waters and accompanies 
nitrate of potash in artificial niter-beds. 
Nitrate of Magnesia (Mg2NO.,) closely resembles _ni- 
trate of lime in external characters and occurrence. It 
may be prepared by dissolving magnesia in nitric acid and 
evaporating the solution. 
Nitrates of Iron.—Various compounds of nitric acid 
and iron, both soluble and insoluble, are known. In the 
soil it is probable that only insoluble basic nitrates of 
sesquioxide can occur. Knop observed (V. S¢., V, 151) 
that certain soils when left in contact with solution of ni- 
trate of potash for some time, failed to yield the latter en- 
tirely to water again. The soils that manifested this 
anomalous deportment were rich in humus, and at the 
same time contained much sesquioxide of iron that could 
be dissolved out by acids. It is possible that nitric acid 
entered into insoluble combinations here, though this 
hypothesis as yet awaits proof. 
* The crystals are, in fact, rhomboidal, 
