PALMITIN 473 



colour-printing, it is highly important that the paint used should bo in the finest 

 possible state. To effect this, at Messrs. De La Rue's and some other large establish- 

 ments, the colours are passed between finely-polished steel rollers which are, by 

 screws, brought very close together. 



PAINTS, VITRIFIABLE. See PORCELAIN ; POTTERY ; and STAINED GLASS. 



PAXiISANDER WOOD. A name employed on the Continent for rosewood. 

 Holtzapffel has the following remarks on this wood : 



' There is considerable irregularity in the employment of this name ; in the work 

 of Bergeron a kind of striped ebony is figured as bois de Palixandre ; in other 

 French works this name is considered a synonym of bois violet, and stated as a 

 wood brought by the Dutch from their South American colonies, and much es- 

 teemed.' 



PAIiIiADXUM, a metal possessed of valuable properties, was discovered in 1803, 

 by Dr. "Wollaston, in native platinum. It constitutes about 1 per cent of the Colum- 

 bian ore, and from to 1 per cent, of the Uralian ore of this metal ; occurring nearly 

 pure in loose grains of a steel-grey colour, passing into silver-white, and of a specific 

 gravity of from 11'8 to 12'14; also as an alloy with gold in Brazil; and it is also 

 found in many varieties of native gold. In the nitro-mxiriatic solution of native 

 platinum, if a solution of cyanide of mercury be poured, the pale yellow cyanide of 

 palladium will be thrown down, which, being ignited, affords the metal. This is the 

 ingenious process of Dr. "Wollaston. The palladium present in the Brazilian gold ore 

 may be readily separated as follows : 



Melt the ore along with 2 or 3 parts of silver, gramilate the alloy, and digest it 

 with heat in nitric acid of specific gravity 1-3. The solution containing the silver- 

 palladium, for the gold does not dissolve, being treated with chloride of sodium 

 or with hydrochloric acid, will part with all its silver in the shape of a chloride. 

 The supernatant liquor being concentrated and neutralised with ammonia will yield 

 a rose-coloured salt in long silky crystals, the ammonio-chloride of palladium, 

 which, being washed in ice-cold water, and then ignited, will yield 40 per cent, of 

 metal. 



Palladium is one of the hardest of the metals ; its colour is not so bright as that 

 of silver ; it is malleable, ductile, and capable of being welded. This metal is more 

 oxidisable than silver, for it tarnishes in air at the ordinary temperature ; when 

 heated in air it becomes blue at first from partial oxidation ; but if the temperature 

 be increased, this colour disappears and its brightness returns. 



Palladium is sometimes substituted for silver in the manufacture of mathematical 

 instruments. The commoner metals may be plated with palladium by the electrotype 

 process. Palladium is sometimes used in the construction of accurate balances, and 

 for some of the works of chronometers. An alloy of palladium and silver is employed 

 by the dentists from the circumstance that it does not tarnish. The influence of 

 palladium in protecting silver from tarnishing is a remarkable and valuable property. 

 The Wollaston medal, given by the Geological Society in honour of its discoverer, was 

 formerly made of palladium. 



PALMITIC ACID. C 32 H 32 4 (C 16 H 32 O 2 ). This acid was first discovered in 

 palm-oil, from which it derived its name ; it has since been found in many other 

 natural productions, and may also be manufactured artificially from many other sub- 

 stances. It is contained, for instance, in bees'-wax, and that in considerable quan- 

 tities ; the portion of the wax insoluble in boiling alcohol is called myricine, and is a 

 palmitate of myricyle. This myricine requires a strong solution of potash to saponify 

 it, and then the palmitic acid is obtained as a palmitate of potash, from which it may 

 be separated by adding an acid. 



Several chemical processes have been introduced for obtaining palmitic acid, but 

 none of them have been used commercially for obtaining it, which is largely used in 

 making candles. When thus required, it is obtained in the same manner as stearic 

 acid, by distilling with high-pressure steam. See CANDLES. 



When pure, palmitic acid is a colourless solid substance, without smell, lighter than 

 water. It is quite insoluble in water, but freely soluble in boiling alcohol or ether. 

 These solutions have an acid reaction, and when concentrated become almost solid 

 on cooling ; but if more dilute, the palmitic acid separates in groups of fine needles. 

 It fuses at 143'6 Fahr. ; and becomes, on cooling, a mass of brilliant pearly scales. 

 It unites with bases to form salts, most of which are insoluble in water. It may also 

 bo made to unite with glycerine to form palmitin, in which state it previously existed 

 in palm-oil. 



PAXilKXTIir. This is the principal constituent of fresh palm-oil. "It may be 

 obtained from it by the following process : 



The palm-oil is subjected to pressure to remove the liquid portions ; the solid por- 

 tion is then boiled with alcohol, which dissolves the free fatty acids which may ba 



