The sulphuric and muriatic acids have little effect upon nickel; the nitric and nitro-muriatic acids are its best solvents.

NIOBIUM is a very rare metal, discovered by H. Rose, in 1845, and said by some to be found with tantalium, which it resembles in some of its properties, in the tantalite of Bodenmais in Bavaria: when the supposed tantalic acid from this source is mixed with charcoal, and heated in a current of chlorine gas, a sublimate is obtained which is a yellow, very fusible and very volatile substance, the chloride of pelopium, and a white, infusible, less volatile body, the chloride of niobium. The niobium may be obtained in a finely divided metallic state by the action of ammonia on the chloride at a high temperature; thus prepared it is black, pulverulent, not acted upon by water, but burning, when heated in the air, to niobic acid, which becomes dark yellow, and has a specific gravity, varying from 4.56 and 5.26.

CHAPTER XXXIV.

NORIUM.

THIS is another rare metal, recently discovered by Svanberg, who states that an undescribed metallic oxide exists in certain varieties of zircon, to the metal of which he gave the name of Norium.

OSMIUM derives its name from osme (smell) on account of its oxide having a peculiar aud pungent smell, somewhat similar to chlorine. It was discovered by Professor Tennant in 1803, in the black powder which is left after that crude platinum has been digested in nitro-muriatic acid. Oxide of osmium may be procured by mixing the black powder with nitre, and distilling at a low heat; oxide of osmium rises into the neck of the retort, in the form of an oily fluid, which after being cooled is a solid, semitransparent mass, soluble in water.

The osmium may be obtained if the pure oxide, dissolved in water, be shaken with mercury, when it will lose its strong smell, and a perfect amalgam is formed; by squeezing the superfluous mercury through leather, and distilling the remainder, a dark grey or blue powder is left which is the osmium.

It has never yet been sufficiently heated to reduce it to a mass; therefore nearly all of its physical properties are unknown. Osmium is unchangeable even in the most intense heat, unless exposed to the air, when it imbibes oxygen, and is converted into a volatile oxide, which is a solid, colourless, semitransparent mass, having a sweet taste, a peculiar odour, and a kind of oily appearance. soluble in water; the solution is colourless, does not alter vegetable blues, and strikes first a purple, and afterwards a blue, with an infusion of nut-galls. When combined with potash it gives an orange coloured solution in water, which imparts to the skin an indelible stain of a dark colour.

It is

Osmium has not been applied to any useful purpose, and its combinations are but little known.

CHAPTER XXXVI.

PALLADIUM.

PALLADIUM (so named on account of its being first obtained in a separate state, about the same time that the new planet Pallas was discovered) was first procured by Dr. Wollaston, in the year 1803, from crude platinum.

It is obtained by dissolving a sufficient quantity of crude platinum in nitro-muriatic acid, and adding a solution of prussiate of mercury, which will gradually precipitate a yellowish white powder, which is prussiate of palladium. If this powder be washed, dried, and exposed to heat, a white mass is left, which is palladium.

It is a white, or rather steel-grey, malleable and ductile metal, somewhat resembling platinum in its appearance, having a specific gravity of about 11.86, and a fusing point somewhat below that of platinum. It is flexible, but not very elastic; when broken it has a crystalline texture. It does not alter in the air, but when kept strongly heated, its surface acquires a blue tarnish; a more violent heat causes it to resume its original metallic appearance.

The only known oxide of palladium was formed by Berzelius, who heated the filings of the metal with potash and nitre; its colour was chesnut-brown.

This metal is soluble in the sulphuric, nitric, muriatic, and nitro-muriatic acids; the solutions have each a red colour.

Palladium possesses the property of destroying the colour of gold, even when alloyed with that metal in the very small proportion of one to five or six.

On account of the very small quantities of palladium which have been obtained, it is not much used, and its combinations are but little known. It is sometimes used for scale pans, chronometer-balances, and in stopping decayed teeth.

CHAPTER XXXVII.

PELOPIUM.

PELOPIUM is a very rare metal, which was discovered in the year 1845, by H. Rose. It exists as an oxide in combination with the oxide of niobium in the tantalite of Bodenmais, in Bavaria; if the supposed tantalic acid from this source be mixed with charcoal and heated to redness in a current of chlorine gas, a sublimate is obtained, which is a yellow, readily fusible, and very volatile substance, the chloride of pelopium, and the white, infusible, less volatile chloride of niobium. The pelopium may be procured in a finely divided state by the action of ammonia upon its chloride, at a high temperature; thus prepared it is black, pulverulent, not acted upon by water, but burning when heated, in contact with the atmosphere, to pelopic acid, which has a specific gravity varying from 5.79 to 6:37.

THIS METAL was discovered in 1741 by Mr. Wood, assaymaster in Jamaica; its name is derived from the Spanish as a diminutive from plata (silver), in allusion to its silvery lustre; hence platina, and its Latin, platinum.

Platinum is comparatively a rare metal, and is found in a metallic state, either nearly pure, or in combination with silex, chromium, palladium, rhodium, osmium, iridium, silver, gold, copper, lead, and iron. It usually is met with in small roundish flattened grains, about the size of sand, but it has occasionally been found in granular pieces as large as a pea. A specimen of native platinum was presented by M. Humboldt, to the King of Prussia, larger than a pigeon's egg; it weighed 1.088 grains, and had a specific gravity of 18.947. The largest mass that has ever been found, weighs

G

more than a pound and three quarters, and is deposited in the Royal Museum at Madrid.

It occurs in the Ural Mountains in Russia, in the silver mines of Guadalcanal, in the province of Estramadura, in Spain; in Ceylon; in the gold mines of Brazil; in the island of St. Domingo; in Choco, and in the mines of Taddo, near Rio-de-la-Plata, in Peru; in New Granada; and in several parts of South America, particularly at Santa Fé, near Carthagena.

The crude platinum is to be dissolved in nitro-muriatic acid, precipitated by muriate of ammonia, and exposed to a violent heat; then the acid and alkali are expelled, and the metal reduced in an agglutinated state, which is rendered more compact by pressure while red hot.

Platinum is the heaviest, not only of all metals, but also, of all solids, as it has a specific gravity of 21:53, which is increased by hammering to 23 66; it is nearly as white as silver, but not so brilliant as that metal; it resists the heat of our most powerful furnaces, but it submits to the heat produced by the oxy-hydrogen blow-pipe; with great labour, it may be rendered malleable, so as to be worked into vessels, like other metals. Like no other metal, except iron, it possesses the valuable property of welding; two pieces of platinum may be united by laying them in contact,. and hammering them, while they are raised to an intense heat. It has great tenacity, and is so ductile that it has been drawn into wire by Dr. Wollaston 1-18,750th of an inch in diameter, and it supported one grain and one third without breaking; a wire 0078 inch is capable of supporting 274 31 lb. avoirdupois. It may, by means of powerful rollers, be reduced to sheets of almost any thinness that may be required. It does not rust or corrode when exposed to either air or water; and is destitute of taste or smell. The ordinary acids, and the immense quantity of chemical re-agents, have likewise no action upon platinum; aqua regia alone dissolves it, and caustic potassa, when fused upon it, oxidizes it. It is a very slow and bad conductor of heat. A great many alloys have been formed with this metal; it may be amalgamated with mercury, but it diminishes the fusibility of this, as well as that of all other fusible metals.

The green and the brown are the only two oxides of platinum known. The green oxide, or protoxide, is obtained