648 



RADICAL 



KAD1SII 



Radical, in t'hemi-tr\. is a term applied to a 

 group roniting "I two or more elementary atoms 

 which in capable of entering into a series of ditler 

 rut compound* without itwlf undergoing change or 

 decoinpoitition. lu this respect a radical resembles 

 an atom of an elementary substance. Radicals 

 are, in a sense, incapable of a separate existence, 

 and must be in combination with other radicals or 

 elements. Two similar radicals can, however, 

 combine with each other, and in such cases the 

 fm|Miund produced has been looked upon as the 

 radical in the free state. 



The radical methyl, CH,, consisting of one atom 

 of carbon and three atoms of hydrogen, is known 

 in combination with chlorine, iodine, oxygen, and 

 Milphur in the respective compounds, methyl 

 chloride, CH 3 C1, methyl iodide, CH,I, methyl 

 <>\ide, (CH,),O, and methyl sulphide, (CHjKS. 

 Two methyl groups occur in combination with 

 each other in the substance ethan or dimethyl, 

 (CH,), or C,H ( . A very large number of other 

 compounds contain the radical methyl. 



The sulphates, the nitrates, and the acetates 

 contain the respective radicals SO 4 , NO,, and 



jj,. These are frequently called the salt- 

 radicals of the respective series of salts. In double 

 decompositions the salt-radical occurring in com- 

 bination with one metal is transferred, without 

 decomposition, to another metal. For instance, 

 the equation 



MgSo 4 + Ba(NO,), = BaSO 4 + Mg(NO,), 



represents the mutual exchange of salt-radicals by 

 the metals magnesium and barium. 



In chemical notation short symbols are frequently 

 employed to represent complicated radicals. Thus, 

 the complex salt-radical of the tartrates, 041140,, is 

 shortly represented by the symlral T. Tartaric 

 acid is then represented by H,T, potassium tar- 

 trate by K.T, potassium hydrogen tartrate (cream 

 of tartar) by KHT, &c. 



Radical, in English politics, is often used to 

 denote the advanced wing of the great Liberal 

 party. The name seems to have been first used in 

 the reign of George III. in the phrase ' radical 

 reform (Anti-Jacobin, 1797 and 1798), though one 

 instance at least occurs much eai HIT in t ho Remains 

 of Archbishop Leighton, written in the reign of 

 Charles II. (see ROOT AMI l!i:ANrii MI:N). But 

 the modern radicals are descendants of the French 

 Revolutionists of 1789. The principal objects of 

 the men so designated have been chielly concerned 

 with parliamentary reform, the extension of the 

 franchise, the enlargement of the public privileges 

 of the people, nml with endeavouring to weaken 

 anil curtail the exclusive privileges and preroga- 

 tives of the oligarchical ruling classes. In a word, 

 the radicals of England have been the pioneers of 

 the democratic movement, and have sought to 

 achieve their ideals almost exclusively through the 

 ii^ency of parliamentary government. The word 

 is meant to indicate the thoroughness of the 

 reform* advocated, lieing derived from tin- Lat. 

 rntliz, 'a root.' Inseparably associated with the 

 great reform movements of the 19th century, the 

 radicals began to lie generally HO called al>ut 1SI6; 

 and the name figured prominently in the move- 

 ments in which Orator Hunt (>|.v.). Thistlewood, 

 Watwin, and others played the chief purls. A 

 clever poom setting forth the aims of tfiefte men, 

 entitled The While Hat (1819) i.e. the hat of 

 Hunt, nicknamed King Harrv the Ninth and 

 written by E. I.. Swifte, will lie found in Note* 

 nml ijiii-rtrit, series 3, vol. x. p. 436. See also \V. 

 Harris, History of the Rat/i*-,*/ 1'nrlii in Parliament 

 ( 1885) ; and 8. Bamford, life of a Radical ( 1842). 



Radiolaria, a class of marine Rhizopod Pro- 

 tozoa. Thread like processes of living matter 

 radiate outwards on all sides ; a membranous cap- 

 sule with fiue pores, or with one or more aperum -. 

 separates an internal nucleated region of the cell 

 from an outer part supported by a gelatinous 

 framework ; there i- a haul skeleton of silica or of 

 a ' horny ' material called acanthin. They multiply 

 by dividing or by forming spores within the central 

 capsule. Most of the Radiolarians are minute, 

 under ,' s of an inch, but a few which form colonies 

 may measure an inch or even 4 inches in length. 

 Most of them include ' yellow cells ' or algie, with 

 which they live in a partnership known RK Sym- 

 biosis (q.v.). Radiolarians occur in all seas, in 

 every latitude, and at all depths, though many 

 kinds predominate on the surface, where they are, 

 wafted about by currents. The siliceous skeletons 

 form most of the ooze which has been dredged from 

 depths of 2000 to 3000 fathoms. F<issil forms are 

 abundant in certain deposits ' liarhadocs earth,' 

 'Tripoli powder,' and various marls, &c. See 

 Haeckel, Report on the Radiolaria (Challenger 

 Reports, xvii., 1887). 



Radiometer, an instrument consisting of four 

 horizontal arms of very fine glass, carefully poised 

 so as to revolve easily on a point ; the tips of the 

 arms having pith discs blackened on one side. The 

 whole is contained in a glass vessel almost but not 

 quite exhausted of air. >Vhen exposed to light or 

 heat the arms move round, more or less swiftly 

 according to the strength of the rays. The black- 

 ened sides of the vanes are warmer : the molecules 

 of air striking those sides are more heated by the 

 vanes : they rebound after impact with greater 

 velocity : the vanes are driven back \y a greater 

 recoil on the blackened sides. The radiometer was 

 invented in 1873-76 by Crookes (q.v.). 



Radiophone, an instrument, essentially simi- 

 lar in principle to the Photophone (q.v.), for pro- 

 ducing sound by means of heat rays. 



Radish (Ranhamts), a genus of plants, of the 

 natural order Crucifera>, having a spongy Silique 

 (q.v.). The flowers are yellow, red, or purple. 

 The Common Radish (A 1 , satimis) has thick, round, 

 tapering, and pointed pods, little longer than their 



Long-rooted and Turnip-rooted Radishes. 



stalks, very slightly contracted between the seeds, 

 and not falling to pieces. It is not known in any 

 country in a wild state, but has been cultivated 

 from time immemorial in China, Japan, India, and 

 in Europe. But some varieties of the Wild Hadish 

 found growingon the Mediterranean coasts resemble 



