PLATE POWDER 



Syracuse, Dec. 5, 1835. In hia 

 Ghaselen, 1821 and 1823, Gedichte 

 (Poems), 1833, and Polenlieder 



( 1'ulisli Sonu's). 



' 1831, he wrote 

 a number of 

 Oriental and 

 other poems 

 thatcontain his 

 best work. Asa 

 dramatist he 

 enjoyed much 

 success, nota- 



Count von Platen- blyinthecome- 

 HaJlermund, dies Die Ver- 

 German poet h a n g n i ssvolle 



Gabel (The Fatal Fork), 1826; and 

 Der Romantische Oedipus (The 

 Romantic Oedipus), 1828, a comedy 

 in which he attacked the exponents 

 of the Romantic movement so 

 strongly as to be himself bitterly 

 attacked by Heine and other writers. 

 Another notable play was Die Liga 

 von Cambrai (The League of 

 Cambrai), 1833. His collected 

 works were published in 1839. 



Plate Powder. Powder for 

 cleaning silverwork. Powdered 

 chalk and jeweller's rouge in the 

 proportions cf three of the former 

 to one of the latter, with enough 

 water to make a paste, forms a 

 plate powder. It is applied wet 

 with a rag, and polished off when 

 dry with a soft cloth or brush. 



Plates. In metallurgy, sheets 

 of metal above 3-16ths of an inch 

 thick. They are made in lengths 

 up to 40 ft., in width up to 12 ft. 

 Ordinary thicknesses run up to 

 If in., armour-plates to 18 ins. 

 Plates are made by rolling out 

 an ingot or a billet while in a 

 highly heated condition. See Iron ; 

 Steel. 



Platform. Raised level surface, 

 something erected above the or- 

 dinary level. Such are used by 

 public speakers, hence a political 

 programme is sometimes called a 

 platform. The word is used for 

 the levels where, at railway sta- 

 tions, passengers enter and leave 

 the trains. In large stations these 

 are numbered. See Railways. 



Platinum. One of the rare 

 metallic elements. Its chemical 

 symbol is Pt ; atomic weight, 195 ; 

 specific gravity, 21-5: melting 

 point, 1,775 C. (3,227 Fah.); 

 colour, tin white or steel grey with 

 metallic lustre. The metal is very 

 ductile, and next to gold and silver 

 the most malleable substance 

 known. It is only exceeded in in- 

 fusibility by two or three of the 

 still rarer metals ; it is not affected 

 by nitric, hydrochloric, or sul- 

 phuric acids in the cold, but is 

 soluble in hot aqua regia. It 

 resists oxidation at any tempera- 

 ture, but is attacked by heated 

 sulphur, phosphorus, arsenic, se- 



6190 



lenium, iodine, and a number of 

 phosphoric compounds. Harder 

 than copper, in the molten state it 

 absorbs quantities of oxygen. 



It was first recognized in the 

 alluvial gold deposits of Choco and 

 Barbacoas, in Colombia, where it 

 was given the name platina from 

 its similarity to plain, silver. It 

 has since been found in the Ural 

 Mts., in Borneo, the Rhine sands, 

 St. Domingo, Tasmania, New South 

 Wales, N. Carolina, U.S.A., Burma, 

 Japan, Spain, Canada, and Brazil. 

 Platinum is mostly found asso- 

 ciated or combined with minute 

 proportions of palladium, rhodium, 

 iridium, and osmium, or one or 

 more of those metals. Before 

 the Great War the chief sources 

 of the metal were the alluvial 

 deposits in the Urals, where it 

 has been for years obtained by 

 dredging. In 1917 the total world's 

 production of platinum was only 

 89,932 oz. 



In obtaining the pure metal the 

 ore is concentrated by washing 

 and the gold removed by amalga- 

 mation as far as may be, after 

 which the mineral is digested in 

 weak aqua regia to dissolve any 

 remaining gold, then in strong 

 aqua regia under pressure, when 

 the metal with iridium and rho- 

 dium enter into solution as 

 chlorides. After filtration, evap- 

 oration, and digestion with water, 

 treatment with ammonium chlor- 

 ide, further digestion with alcohol, 

 drying and heating, the metal is 

 obtained in the form of a spongy 

 mass, which is compressed at a 

 high temperature to a metallic 

 form in which it may be utilised in 

 the manufacture of vessels. 



PLATO 



Platinum black is an extremely 

 finely divided form of the metal 

 and has a remarkable power of oc- 

 cluding hydrogen and oxygen, as 

 has spongy platinum. The metal 

 is used in the manufacture of strong 

 sulphuric acid ; in the construc- 

 tion of electric lamp bulbs ; in the 

 preparation of standard weights 

 and measures, crucibles, pyro- 

 meters, and other implements for 

 chemical laboratories ; in dentistry 

 for the preparation of plates and 

 anchors ; in photography, as potas- 

 sium chloroplatinite, in the plati- 

 notype process ; and for jewelry, 

 for which latter purpose it is 

 generally alloyed with 25 p.c. of 

 iridium, which increases its strength 

 and hardness. See Metal ; consult 

 also The Precious Metals: Gold, 

 Silver, Platinum, T. Kirke Rose, 

 1909 ; A Handbook of Metallurgy, 

 C. Schnobel and H. Louis, 3rd 

 ed. 1921. 



Platinum Printing. Process of 

 making permanent photographs or 

 platinotypes. Paper is rendered 

 sensitive to light by application of 

 an iron salt, ferric oxalate, with 

 which is mixed one of platinum, 

 potassium chloroplatinite. On ex- 

 posure to light under a negative a 

 semi-visible image is produced. 

 It is brought to full depth in a 

 solution of oxalate of potash, and 

 is then passed through several weak 

 acid baths to remove the iron 

 salts. After a short washing in 

 water, the print is ready to be 

 dried. Platinum paper is pre- 

 pared to give either black or sepia 

 prints, which have the natural sur- 

 face of the paper, since there is no 

 gelatin coating as in emulsion 

 papers. See Photography. 



PLATO AND PLATONISM 



T. Callander. M.A., Professor of Greek, Queen's University, Kingston 



Related articles are those on Aristotle; Socrates; and other great 



philosophers. See Academy ; Idea; Neo-Platonism ; Philosophy; 



Sophists ; also Greece ; Greek Literature 



Born at Athens, or in the island 

 of Aegina, of distinguished family, 

 Plato spent most of his life in the 

 city of Athens, immersed in the 

 study and the teaching of philoso- 

 phy. He is said to have visited 

 Egypt, Magna Graecia, and Sicily, 

 and to have been captured and 

 sold as a slave at Aegina, but the 

 trial and execution of his master 

 Socrates, 399 B.C., was by far the 

 most moving incident in his career. 

 Henceforth there was only one 

 career for him, to carry on the 

 mission of his martyred teacher. 

 The record of that mission is set 

 forth in the rich collection of 

 Dialogues that have come down 

 to us. Of the 35 treatises many 

 critics reject the Letters ascribed 

 to Plato, some 24 are probably 



from his hand. Through these 

 works his influence has been per- 

 petuated to the present day. 



In the make-up of Plato are 

 discerned three strains seldom 

 found so conspicuously united in 

 a single mind. The acuteness and 

 subtlety of the logician, the 

 imagination of a seer and poet, 

 and the enthusiasm of a shrewd but 

 austere moralist are his in the 

 highest degree. Typical of the 

 first is the Theaetetus, with its 

 keen analysis of logical scepticism 

 as taught by Heraclitus and Pro- 

 tagoras ; the second strain is 

 dominant in the Phaedo and 

 Phaedrus ; the third in the Laws ; 

 while the Republic exhibits in per- 

 fection the blending of all three. 



Plato, or Aristocles, as he was 



