IRO 



ISO 



1. lodal (iodine and alcdho]). An ole- 

 aginous liquid obtained by the action of 

 iodine upon nitric alcohol. 



2. Iodic Acid. An anhydrous acid, 

 tanned oxiodine by Davy, and produced 

 by the combination of iodine with oxy- 

 gen. It combines with metallic oxides, 

 and forms salts which are termed 

 iodates. 



3. Iodides, or lodurets. The compounds 

 of iodine with metals, and with the sim- 

 ple non-metallic substances. 



4. lodous Acid. A compound prepared 

 by the action of iodine on chlorate of 

 potash, — probably by the combination of 

 iodine and chlorine. 



5. Chloriodic Acid. This is also called 

 chloride of iodine ; and is formed by the 

 absorption of chlorine by dry iodine. 



I'OLITE. A variety of quartz, inter- 

 mediate in colour between violet-blue 

 and blackish-blue, occurring in primitive 

 rocks in Finland. 



FON (ioi/, that which goes ; neut. part, 

 of eim, to go). A term introduced by 

 Faraday, explanatory of his views of 

 electrolysis. He is of opinion that the 

 force does not emanate from the poles of 

 the battery, but that it resides in the 

 substance undergoing decomposition, of 

 which one element, or ion, goes to the 

 positive, the other element, or ion, to the 

 negative, end of the battery. The ion 

 which goes to the anode, or positive pole, 

 he terms an-ion ; that which goes to the 

 kathode, or negative pole, kat-ion. See 

 Electrode. 



IRIDA'CE^. The Cornflag tribe of 

 Monocotyledonous plants, represented by 

 the iris and the crocus. Smooth herba- 

 ceous plants, with leaves e(\n\ia.nt', flowers 

 hexapetalous, triandrous; stamens 3; 

 ovarium 3-celled, many-seeded. 



IRIDE'SCENT {iris, a rainbow). The 

 property of shining with many colours, 

 like the rainbow. 



IRIDINI'NiE. A sub-family of the 

 Unionidcs, or River Mussels, named 

 from the genus iridina. 



IRI'DIUM {iris, sl rainbow). The 

 most infusible of all known metals, 

 named from the variety of colours it dis- 

 plays while dissolving in hydro-chloric 

 acid. 



IRON. The most abundant of the 

 true metals, occurring in the form of 

 oxides and clay iron-ore, and entering 

 into the composition of many rocks, 

 which frequently owe their grey colour 

 to it. 



Cast or pig iron is the name given to 

 184 



the metal when first extracted from its 

 ores. Its varieties are the white cast 

 iron, which is extremely hard and 

 brittle, and appears to consist of small 

 crystals ; grey or mottled cast iron, so 

 called from the inequality of its colour, 

 softer and less brittle than the preceding ; 

 and black cast iron, the most unequal 

 in its texture, and least cohesive of the 

 three. 



IRON-PYRITES. Yellovj sulphuret 

 of iron. An ore of iron, of a brass-yellow 

 or greenish-yellow colour, compact or 

 fibrous, emitting a sulphurous smell 

 when struck ; granulated, or even earthy, 

 when impure. 



IRONSTONE. A stratum of the coal- 

 formation, forming thin beds, or disposed 

 in globular or depressed masses, alter- 

 nating with layers of shale. It is of a 

 brown or grey colour, and is principally 

 composed of iron combined with oxygen, 

 carbonic acid, and water, usually with a 

 little alumina, silica, and lime. 



IRRA'TIONAL NUMBERS. A term 

 applied, in Algebra, to those numbers or 

 quantities, the roots of which are incom- 

 mensurable by unity, and the exact value 

 of which can therefore never be deter- 

 mined ; in other words, to those num- 

 bers or quantities which are inexpres- 

 sible by an arithmetical ratio, and are 

 therefore " arithmetically irrational." 

 These numbers are generally called 

 surds, from the Latin surdus, deaf or 

 senseless. 



IRREDU'CIBLE CASE. An alge- 

 braical term, applied to that class of 

 cubic equations in which Cardan's for- 

 mula fails in its application. The reason 

 of the failure arises from the imaginary 

 expression of the formula, and from the 

 fact that the cubic equations in question 

 have all the three roots real. 



IRREGULAR BIVALVES. Those 

 bivalves which are not uniform in shape 

 throughout the species ; a deviation al- 

 most confined to the perforating groups. 



IRREGULAR MASSES. A term 

 applied by MacCulloch to rocks of no 

 determinate form, and of any size, as 

 granite, greenstone, and porphyry. 



I'SERINE. An iron-black mineral, 

 containing titanium and uranium, found 

 near the origin of the river Iser, dis- 

 seminated in granite sand, and in allu- 

 vial soil, together with pyrope, in Bo- 

 hemia. 



ISO- {'iffo9, equal). This prefix denotes 

 equality, or similarity. Hence,— 



1. Iso-barysm {ftdpos, weight). Simi- 



