PLATFORM. 



PLATINUM. 



603 



side, or in certain parts, and these obtain the designation of miter-gilt 

 The whole trade, however, has undergone a revolution within the last 

 few years, by the introduction of the process of electro-metallurgy, or 

 electro-plating. By this process a work of art may be made wholly o 

 gold or silver, or of a film of those metals on a ground of less value, bi 

 deposition from certain chemical liquids through the agency of a 

 galvanic battery. The processes are explained under ELECTRO 

 METALLURGY. The annexed wood-cut will illustrate the remarkable 



ecries of operations (as described in that article) by which the better 

 kinds of electro-plate are produced: a is a model for a silver cup, 

 formed of wax or composition, and sculptured with an artistic design 

 on the outer surface; b is one half of an elastic mould, made of 

 caoutchouc and other substances, and obtained by casting from the 

 model, with the device inside instead of out ; c is a copj>er cup obtained 

 by electro-deposition upon the interior of the mould, and afterwards 

 dutached from it ; d is the finished cup, with an electro-silver surface 

 upon an electro-copper ground, and a handle attached. If possible, 

 white metal is used instead of copper as a basis. 



There are many curious modes of coating plates of metal with thin 

 films of other metal, wholly distinct from those in which gold and 

 silver are employed. Most of them, however, bear analogy to TI.NM.VG 

 or TIX-PLATIXI;, and will be briefly adverted to in that article. 



PLATFURM, Military, is the floor of wood or stone on which 

 heavy guns are placed in order to be more easily worked. In fortresses 

 the platforms are occasionally made of stone in order to withstand 

 long exposure to the weather, but in field-works they are always of 

 timber. For guns the platforms are laid with a slight rise to the 

 rear (about \ inch in the foot) to enable the gun to be more readily 

 run up after the recoil. The mortar platforms are laid level. The 

 ordinary gun and howitzer platform which, when laid, forms a 

 rectangle 15 ft. long by 10 ft. 6 in. broad, consists of the following 

 pieces : 



5 sleepers, each 15 feet long x 5 in. x 5 in. 

 20 planks 104 9 2 



2 ribbands 15 4 4 



10 rack-sticks and lashings, or iron bolts. 



The weight of the platform is about 1 4 cwt. 



The sleepers are first laid in the direction of the line of fire in cuts 

 or trenches made in the ground, which has been previously levelled, 

 and are firmly pinned down. They are then covered with the planks, 

 which are laid at right angles to the line of fire, and, the ribbands being 

 placed directly over the outside sleepers, are fixed down by the rack- 

 lashings, which have been placed, five on each side, under the sleepers 

 before they were laid. 



The platforms may be fixed with screws, or spikes, instead of rack- 

 lashings ; but this, besides injuring the wood for further use, should it 

 be necessary to move them, is a noisy operation, likely to attract the 

 enemy's attention if the batteries are close to his works. 



There is a description of gun-platform invented by Colonel Alderson, 

 U.E., in which all the pieces, superstructure, and sleepers are of the 

 lame size, and are fitted together with dowel ping. 



Platforms for mortars, which are laid horizontally, are generally 

 7 ft. 6 in. by 6 ft. 6 in. In order to resist the effect of the recoil of 

 the mortar, which is fired at an angle of 45, the sleepers and planks 

 are stronger than in the gun-platform, and seven sleepers are used 

 instead of five. Two sleepers being first laid transversely, then the 

 five across them, and then the planking. 



<> flalfurnw for guns are composed of a strong framework of 

 wood, consisting of two side .pieces, 12ft. Gin. long and 9 in. x 4 in., 

 on which the wheels of the gun run, and two trail pieces 12 ft. 6 in. long 



ARTS AND SCI. DIV. VOL. VI. 



and 4 in. square, for the trail of the gun (this platform being used 

 for guns on travelling carriages). The whole platform is kept together 

 and strengthened by a front and rear transom and three sleepers, to 

 which the aide and trail pieces are bolted down. The front transom is 

 fixed close to the parapet, and the platform has a rise to the rear of 

 8 inches. This platform is very good for siege purposes, and when no 

 great lateral splay is required ; for when it is necessary to change the 

 line of fire the whole platform has to be traversed with handspikes. 

 Siege platforms, as has been stated, are generally made rectangular ; 

 but the stone platforms used in permanent works are made wider at 

 the rear, so as to allow the guns a greater splay. This is not so much 

 required in siege works when the guns have a fixed object, and would 

 further make the platforms more complicated and difficult to lay at 

 night, while the pieces not being uniform would not be interchangeable. 



In fortresses, at the salients and in casements, and in coast batteries, 

 the guns are now often mounted on traversing platforms. The gun is 

 then raised on a platform which traverses on runners, the pivot being 

 fixed either in front, centre, or rear. 



PLATINAMINE. [PLATINUM.] 



PLATING-HYDROCYANIC ACID. [CYANOGEN; HYDROFLATINO- 

 OXANM ACID.] 



PLATINUM (Pt). The natural history of this metal has already 

 been given. [PLATINUM, in NAT. HIST. DIV.] It has been very much 

 used during the last fifty years in those experimental and manufacturing 

 operations in which vessels are required that are not acted upon by 

 hydrochloric, nitric, or sulphuric acids. Platinum knives, crucibles, 

 capsules, and dishes, are commonly employed ; while stills weighing 

 from five hundred to ne thousand ounces are not unfrequently made 

 use of for concentrating oil of vitriol. 



The metallurgy of platinum has of late years received considerable 

 attention, and been greatly improved by MM. Deville and Debray. 

 Their memoir appears in the ' Annales de Chimie et de Physique ' for 

 August, 1859, and is abstracted in the ' Pharmaceutical Journal 'and 

 ' Chemical News ' : its title is, " On Platinum and its Associated 

 Metals." The following .table exhibits at a glance the composition of 

 platinum ores from various sources ; for details concerning methods of 

 analysis, see the paper above referred to. 



The preparation of pure platinum from the ore is effected as follows. 

 The ore is fused in a reverberatory furnace with an equal weight of 

 galena, care being taken to avoid as far as possible any rapid oxidation 

 of the lead. The mass is well mixed so as to convert all the iron into 

 sulphide, and to produce an alloy of the platinum with lead ; some 

 glass is then added, and sufficient litharge to effect the decomposition 

 of all the sulphides. The metal is then allowed to remain perfectly 

 undisturbed for some time in order that the osmides may settle down 

 and collect in the lower portion of the mass. The scoria is then 

 removed ; the alloy of platinum and lead run off, except the lowermost 

 portion which contains osmium, and the lead finally removed by the 

 ordinary process of cupellation. The fusion and refining of the 

 resulting platinum are effected in furnaces made of solid lime and 

 heated by a large jet of oxygen and hydrogen gases. 



Nearly all the platinum at present met with in commerce contains 

 traces of osmium and a little silicium, but these may be perfectly 

 removed by prolonged fusion in the oxyhydrogen furnace j ust mentioned. 



Pure platinum is a white metal of the same softness as copper, and 

 is susceptible of high polish. It slowly volatilises at a temperature 

 considerably above its melting point, and, on quickly cooling, bubbles 

 and spirts like silver. In tenacity and ductility it is superior to all 

 metals except iron. Its specific gravity is 21'15 ; or after hammering, 

 21'5. As a conductor of heat and electricity, it is inferior to gold and 

 silver. It has the property of condensing gases on its surface, and 

 when once heated to redness remains red hot for some time if a jet of 

 cold hydrogen or coal gas be impinged upon it. Platinum is not 

 arnished by exposure to air, is unaffected by all acids except aqua 

 regia, and is not acted upon by dry chlorine. It very readily combines 

 with other metals, so that nothing that contains, or is likely to yield, a 

 metal as such, should be heated in vessels of platinum. Alkalies also 

 corrode it through formation of a double oxide. 



Chlorides of Platinum. Platinum dissolves in a mixture of three 

 )arts hydrochloric acid and one part nitric acid. Such a mixture 

 aqua regia) contains free chlorine, which unites with the platinum to 

 :orm bichloride of platinum (PtCl,). The latter may be obtained in 



o o 



