TIIK NITUIO ACID OK 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; il 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 ni 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 (Ca^NO^) may be obtained as a white 

 mass or as six-sided crystals by dissolving lime in nitric 

 acid and 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 i)otash in artificial niter-beds, 



IVitrate of Maj^nesia (Mg2N0J closely resembles ni- 

 trate of lime in external chaiacters and occurrence. It 

 may be prepared by dissolving magnesia in nitric acid and 

 evaporating t.he sohition. 



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 ( F! St., 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 arc, in fact, rhomboiUal, 



