PLATINUM 



4702 



PLATO 



palladium and ruthenium, in addition to a lit- 

 tle iron, copper, chromium and titanium. Oc- 

 casionally large nuggets of native platinum are 

 found. The ore contains from sixty to eighty- 

 five per cent of pure platinum. 



Production and Distribution. The world's 

 output of platinum averages about 300,000 

 ounces a year. About eighty-five per cent 

 comes from Russia, whore the ore is found in 

 the Ural Mountains. The next largest supply 

 comes from Colombia, in South America. It 

 is also found in very small quantities in Canada, 

 Australia, New Zealand and the islands of 

 Borneo and Sumatra. From the gold-bearing 

 deposits of California, Oregon and Nevada 

 about 600 ounces are extracted a year. Besides 

 considerable amount is extracted in the 

 United States in the process of refining gold 

 and copper. From this source 3,100 ounces of 

 pure platinum were produced in 1916. 



Properties. Platinum is a chemical element 

 (symbol Pt). It is grayish-white in color and 

 is one of the heaviest substances known, its 

 specific gravity (see GRAVITY, SPECIFIC) being 

 21. It is highly malleable and ductile (see 

 I)t ( TILJTY; MALLEABILITY) and in these proper- 

 ties is surpassed only by gold and silver. It 

 melts at the high temperature of 3200 Fahren- 

 heit. 



Platinum is not oxidized in the air, and it is 

 not attacked by any of the pure acids. It dis- 

 solves only in aqua regia (which see) or nitro- 

 muriatic acid and in mixtures which generate 

 chlorine. Platinum combines directly with 

 phosphorus, arsenic, silicon and with almost all 

 other metals. It forms useful alloys with gold, 

 silver, steel and iridium. See ALLOY. 



Uses. On account of its power of withstand- 

 ing heat and the action of chemical reagents, 

 platinum is much employed as a material for 

 making vessels and crucibles which are used in 

 chemical laboratories and in many chemical in- 

 dustries. It also fills an important place in the 

 manufacture of sulphuric acid, where it acts as 

 a catalyzer, that is, as a substance which by its 

 presence helps the chemical combination of 

 other elements. Platinum is valued by makers 

 of expensive jewelry, for it is considered to be 

 the best setting for precious gems, and dentists 

 employ it in the teeth. The alloy of platinum 

 with iridium, a rare metal of the same group, 

 possesses an excellent and unalterable surface 

 for fine engravings. The standard units of 

 weights and measures are made from this alloy. 



Consult Rose's The Precious Metals, Compris- 

 ing Gold, Silver, and Platinum. 



PLATO, pla'toh (427-347 B.C.), one of the 

 greatest of Greek philosophers, was born on the 

 island of Aegina, belonging to Athens. His 

 father was Ariston, a descendant of Codrus; 

 his mother, Perictione, was said to have been 

 of the line of Solon. In his youth he received 

 the customary education of the age, and tradi- 

 tion states that he wrote poetry and won dis- 

 tinction in gymnastics; also, that through the 

 influence of Socrates he turned to philosophy 

 at the age of twenty. Without positive basis 

 of truth it is also said he traveled extensively in 

 Greece, Sicily, Italy, Egypt and Northern 

 Africa; and that Dionysius of Syracuse sold 

 him into slavery at Aegina, though friends res- 

 cued him immediately. In 387 B.C. he was in 

 Athens, and there established his school, the 

 "Academy," on an estate one mile from the 

 city. The last years of his life are wrapped 

 in obscurity, and the numerous legends regard- 

 ing him have been almost entirely discredited. 



There is no evidence that any of Plato's writ- 

 ings have been lost, but many formerly ac- 

 credited to him are now regarded as not his. 

 His works are all in the form of dialogues, in 

 which he attained unparalleled depths of 

 beauty, truth and grace. The important ones 

 include Laches, Charmides, Lysis, Protagoras, 

 lo, Meno, Euthyphro, Apologia, Crito, Phacdo, 

 Symposium, Phaedrus, Cratylus, Gorgias, the 

 Republic; the dialectical or argumentative dia- 

 logues Timaeus, Critias and the Laws. The 

 Euthyphro, Apologia, Crito and Phaedo refer 

 especially to the trial and death of Socrates, 

 who appears in each of them as the man of 

 ideal piety, the reformer, the law-abiding citi- 

 zen, the recluse dwelling on eternal themes. 



His greatest work is the Republic, in which 

 are outlined plans for an ideal State. Its pur- 

 pose was to be the training of citizens to be- 

 come virtuous; its aim, the true happiness of 

 the individual. Although Plato realized that 

 this ideal commonwealth could never be at- 

 tained in an imperfect world, he constantly 

 held it up as an end toward which all should 

 strive. In it each human soul would be best 

 fitted for its proper work. The citizens would 

 be divided into three classes, according to ihe 

 three dominant virtues of the soul the govern- 

 ing class (whose virtue is wisdom) ; the military 

 (valor); the industrial (self-restraint and will- 

 ing obedience). Art, the Beautiful, and all 

 other things would be subordinate to the Good. 



It is practically impossible to formulate Pla- 

 to's system of philosophy in a few sentences. 

 An eighteenth century writer thus summarizes 



