IRO 



IRR 



3718. This is the black oxide, and 

 exists in green vitriol and the proto- 

 salts of iron, serving as a base. 2d. 

 The peroxide, 2 Fe + 3 = 78-36. 

 This is the common red or brown 

 oxide ; it is also a base, producing 

 the persalts of iron. Iron is readily 

 dissolved by acids, being tirst oxidi- 

 zed, and then uniting with the acid. 

 The salts of the protoxide are, for the 

 most part, instable, changing to per- 

 oxides when exposed to moist air. 



Iron is discovered in solution by 

 an infusion of gall-nuts, which, soon- 

 er or later, produces a black colour 

 (ink). If the colour arises immedi- 

 ately, tlie peroxide is present ; if the 

 mixture requires stirring and expo- 

 sure to air, the protoxide is present. 



Many of the compounds of iron are 

 of great interest to the farmer. The 

 protosulphate (copperas) is much used 

 in dyeing, in makmg ink, and as an 

 emetic. In Switzerland it is added to 

 urine and fluid manures, to fix their 

 ammonia, which it converts into a 

 sulphate. It is also powerfully disin- 

 fecting, removing bad smells. This 

 body is sometimes present in marshy 

 and peaty soils, and makes them per- 

 fectly barren ; they are, however, 

 quickly recovered by liming. The py- 

 rolignate of iron (persalt) is used in 

 dyeing and the preservation of timber. 

 The muriate has the same properties, 

 and is also a medicine. Prussian blue 

 is a sesquiferrocyanide of iron. 



The iron work of the farm should 

 be painted with coal-tar for protec- 

 tion from rust, or kept in a dry place 

 under cover. Portable fencing, hur- 

 dles, and many other fixtures on a 

 farm are now made of iron, which 

 heretofore were wooden. It is well 

 adapted for the sashes of hot-houses : 

 wire is extensively employed for 

 slight trellises. Wires should be pro- 

 tected from moisture by coal-tar, or 

 other coarse paint. 



IRON PYRITES. Native sulphu- 

 ret of iron ; it forms a mineral often 

 crystallized, of a golden colour. Its 

 presence in soils produces barren- 

 ness, which is soon rectified by li- 

 ming ; it is the origin of most of the 

 sulphur springs. Water flowing over 



the pyrites decomposes it in part, 

 and becomes tainted with sulphuret- 

 ted hydrogen. 



IRON WOOD. See Homhcam. 

 IRRADIATION. The brightness 

 that surrounds luminous objects, and 

 increases their apparent size. 



IRRIGATION. " Of all the sub- 

 stances which concur in the vegeta- 

 tion and growth of plants, water is 

 the most essential ; without moist- 

 ure the seed cannot germinate, nor 

 can the plant receive nourishment. 

 Hence in warm climates, where rains 

 are periodical, and where the soil is 

 dried and parched by a continued 

 evaporation, no verdure exists, ex- 

 cept where springs or rivers supply 

 the waste of moisture. The warm- 

 er the climate, and the more rapid 

 the evaporation, the more luxuriant 

 is the vegetation, provided there be 

 an abundant supply of water. This 

 circumstance has suggested the plan 

 of diverting streams and conducting 

 them in channels to fertilize as great 

 an extent of land as possible. The 

 water used always contains saline 

 and other matters very necessary to 

 the growth of plants, and which are 

 supplied by irrigation. 



" If water stagnates and is evapo- 

 rated, and the noxious matter held in 

 solution remains in the soil, all the 

 advantage of irrigation is lost, and 

 the better kinds of grasses are suc- 

 ceeded by rushes and coarse aquatic 

 plants, as may be seen in all marshy 

 spots. The circulation of the water, 

 therefore, appears to be as necessary 

 as its presence ; and, provided there 

 be a sufficient supply of water of a 

 proper quality, the more porous the 

 soil, and especially the subsoil is, 

 the more vigorous is the vegetation. 

 It is on this principle alone that we 

 can rationally account for the great 

 advantage of irrigation in those cli- 

 mates where rain is abundant, and 

 ' where the soil, which is most benefit- 

 j ed by having a supply of water run- 

 I ning through it, is of a nature to re- 

 I quire artificial draining as an indis- 

 pensable preliminary to being made 

 fertile by irrigation. By keeping 

 \ these principles in view, great light 



435 



