Vol. XXII. No. 4.] 



POPULAE SCIENCE NEWS. 



53 



Prattital C5emtotrp anH t^e artct. 



PLATINUM. 



When the early Spanish explorers found in 

 the alluvial deposits of South America grains 

 of a hard white metal heretofore unknown to 

 them, the}- considered it to be an inferior kind 

 of silver, and gave to it the name phitina, a 

 diminutive of the Spanish word for silver. p/n^(. 

 It was not thoroughl}' studied until 17o2, when 

 Scheffer, the director of the Swedish mint, pub- 

 lished a full account of the new metal. Since 

 that time its applications in the arts have been 

 constantly increasing, but its use is greath" 

 restricted by its scarcity and consequent high 

 price. 



Platinum is always found native, or in the 

 metallic state, but is usually alloyed more or 

 less with iridium, osmium, and other metals of 

 the so-called platinum group, as well as iron 

 and the more common ones. The annual prod- 

 uct of platinum is between two and three tons, 

 of which the United States furnish about two 

 hundred ounces. When separated from its 

 impurities, and worked into scientific appara- 

 tus, it is worth from ten to fifteen dollars an 

 ounce ; but since the general introduction of 

 electric lighting, such a demand for platinum 

 wire has arisen, that the price is constanth- 

 tending upward. 



Platinum is one of the heaviest metals known. 

 its specific gravity (21.5) being only slightly 

 exceeded by iridium and osmium. It is only 

 fusible in the heat of the oxyhydrogen flame 

 at a temperature of 1480°, and will dissolve only 

 in nitro-hydrochloric acid. This refractory 

 nature renders it verj* suitable for crucil)les, 

 dishes, and other apparatus used by chemists. 

 Large retorts of platinum are used in the manu- 

 facture of sulphuric acid, for concentrating the 

 weak acid by evaporation. A retort capable 

 of concentrating eight tons of acid daily, costs 

 over eight thousand dollars. In the A'ear 1828 

 the Russian government commenced coining 

 the metal, but discontinued it in 1845. It is 

 also very largely used, as stated above, in the 

 manufacture of incandescent electric lamps. 



Platinum is extensively used in dentistry in 

 the form of rivets for fastening artificial teeth 

 to the rubber or celluloid plate. After the 

 teeth are worn out, the rivets are bought by 

 dealers in platinum scraps, and worked over 

 again. Certain mysterious and suggestive ad- 

 vertisements for second-hand sets of teeth 

 which occasionally' appear in the newspapers 

 are thus susceptible of a simple and reassur- 

 ing explanation. 



Formerl}- platinum was obtained from its 

 ores by a tedious process of dissolving in acid, 

 and precipitating the metal in a finely- divided 

 condition known as platinum black, which was 

 consolidated by pressure into a form suitable 

 for working. The more usual process is bj- 

 smelting with lead ore, which removes most of 

 the impurities. The lead is afterwards re- 

 moved by cupellation, and the platinum 

 re-melted in a limestone crucible b}- the oxy- 

 hydrogen blowpipe, to further purify it. In 

 1862 a firm of platinum-workers exhibited in 



London an ingot of pure platinum weighing 

 two hundred and fifty pounds, and valued at 

 twenty thousand dollars. 



Platinum is extremely ductile, and can be 

 drawn out in a wire thinner than a spider's 

 web. This is accomplished by covering a fine 

 l)latinum wire with silver, and drawing the 

 whole out together, after which the silver is 

 removed by dissolving in nitric acid. 



Platinum when in a finely divided condition 

 possesses the remarkable property of absorbing 

 and condensing large quantities of gases, espe- 

 cially oxygen. If a jet of hydrogen or illumi- 

 nating gas is directed upon a small mass of 

 spongy platinum or platinum black, the gas 

 combines with the oxygen absorbed in the 

 metal ; and this combination is attended with so 

 muck heat, that the platinum becomes red-hot, 

 and finally causes the ignition of the gas-jet. 

 This experiment can also be performed with a 

 l)iece of platinum wire or foil, if it is first heated 

 to redness, and placed in the gas-jet before it 

 becomes quite cold. 



Notwithstanding its highly refractory 

 nature, apparatus made of platinum must be 

 handled with considerable care. Although 

 platinum by itself is very infusible, it easily 

 unites with other metals at a low tempera- 

 ture, forming readily fusible alloys. Many an 

 expensive crucible has been ruined through the 

 inexperienced or careless experimenter at- 

 tempting to ignite a salt of lead or zinc in it. 

 Phosphorus, sulpliur, and caustic potash also 

 attack it, and even eeitain parts of the flame of 

 a Buusen burner will disintegrate it in time. 

 Solutions which give off chlorine gas must also 

 be kept away fi'om platinum dishes, and of 

 course nitric and hydrochloric acids must never 

 be mixed together in therj^ Platinum vessels 

 will last much longer if always kept bright and 

 clean. Gentle rubbing with sea sand gives a 

 fine i)olish ; or, if the interior is verj- dirtj', 

 borax or bisulphate of potash may be fused 

 in them. 



Very little platinum apparatus is produced 

 in this countrj-. As far as we know, a factory at 

 Sugartown, Penn., is the only one in the United 

 States. A few firms in London and Paris 

 manufacture a large proportion of the platinum 

 used in the arts ; but the American product is 

 fully equal, in point of finish and durability, to 

 that made in Europe. 



which is obtained as follows: Finely fmwdered per- 

 oxide (dioxide) of barium, or the commercial 

 so-called hydrated peroxide, is added to dilute 

 hydrochloric acid until the latter iu nearly satu- 

 rated. The solution is filtered and cooled, and 

 then mixed with just enough solution of baryta to 

 precipitate the foreign oxides and silica, and to 

 produce a small precipitate of hydrated peroxide of 

 barium. It is then again filtered, and, by addition 

 of concentrated solution of baryta, the hydrated 

 peroxide of barium precipitated in a crystalline 

 state. This may be preserved in a moist condition 

 for a long time without spoiling, provided it is kept 

 in air-tight vessels. 



The products of the reaction are insoluble car- 

 bonate of barium and a solution of hydrogen per- 

 oxide. When a considerable amount of the former 

 has been produced, it is allowed to deposit, the 

 clear solution removed, and the process continued 

 as before. The liquid must be kept cold, towards 

 the end, by the application of ice ; and care must 

 be taken that there is always an excess of carbonic- 

 acid gas, which should keep the precipitate as it 

 forms in suspension, and prevent it from settling 

 to the bottom. The small amount of barium which 

 remains finally in solution as bicarbonate, may be 

 precipitated by the addition of a few drops of dilute 

 sulphuric acid. A small excess of the latter is an 

 advantage, as it will cause the product to keep 

 better. 



The advantage of this method is, that it does not 

 require any filtration, and that it furnishes a per- 

 fectly pure product if the hydrated peroxide of 

 barium has been used. A vital condition of suc- 

 cess is to add the peroxide in small quantities at a 

 time, and if it is in a dry condition, to have it in 

 the finest possible powder. 



The preparation of peroxide of barium on a 

 large scale, for the pui-pose of employing the prod- 

 uct in the manufacture of hydrogen perox'ide, is 

 carried on by passing moist atmospheric air, freed 

 from carbonic-acid gas, over anhydrous baryta 

 raised to faint redness in iron retorts. — Druggists' 

 Circular. 



PREPARATION OF PEROXIDE OF HYDRO- 

 ,GEN ON A LARGE SCALE. 



Which particular process is used by the different 

 makers of peroxide of hydrogen is not known to 

 us; but it is evident that the largest manufacturers 

 of this article, who turn out many thousand 

 pounds a week, cannot employ the usual methods 

 quoted in chemical text-books. On glancing over 

 the literature of the subject, we find that Duprey's 

 process appears to have the best chance of being 

 employed on a large scale, at least among those 

 which have been published. The process is as fol- 

 lows: — 



A rapid stream of carbonic-acid gas is conducted 

 through cold water, and to it are gradually added 

 small portions of peroxide of barium reduced to 

 an impalpable powder. According to Otto, it is 

 preferable to use the hydrated peroxide of barium, 



SCIENTIFIC RAILROAD-BUILDING. 

 The first train of cars has crossed the long bridge 

 that has been thrown over the Oxus River in Rus- 

 sian Central Asia This structure, which is nearly 

 a thousand feet longer than the Brooklyn Bridge, 

 including its approaches, spans a classic river, of 

 which very little was known thirty years ago, ex- 

 cept through the writings of the old historians, 

 who described the exploits of Alexander and 

 Tamerlane. The man who ten years ago had pre- 

 dicted that to-day iron rails would stretch over 

 wide deserts and the upper course of the famous 

 Oxus, which had been reached in modern times by 

 only three or four disguised white men, would have 

 been looked upon as a visionary enthusiast. The 

 road-bed has been graded for nearly the entire dis- 

 tance between the Oxus and Samarcand; and, with 

 the completion of the bridge, the work of laying 

 the track will rapidly proceed. Within the next 

 three months it is expected that the trans-Caspian 

 railroad will be completed to Samarcand, and trains 

 running from the Caspian Sea to the capital of the 

 great Mongol conqueror. This road is remarkable, 

 not only because it pushes far into inner Asia, but 

 also because some unique problems in railroad con- 

 struction have been solved by its successful prog- 

 ress. Many engineers said a railroad could not be 

 maintained through the shifting sands of the Kara- 

 Kum desert. But General Annenkoff, by covering 

 parts of his roadway with clay, by placing in his 

 embankments layers of the branches of a desert 

 shrub, and by cultivating along parts of the route 

 many thousands of desert plants whose roots retnin 



