CHEMISTRY. 





Elements though inferior in this respect to iron, nickel, and 



/ cobalt. Acids act upon it with great difficulty. It 



Chemistry. re q U j res a vcr y high temperature to melt it, so that 



^"Y"" hitherto it has only been obtained in small grains. 

 Oxide*. 2. Chromium is not altered by exposure, but when 



heated in the open air, it is gradually oxidized. 

 Three oxides of this metal are known. 



The protoxide, or green oxide, may be obtained 

 by exposing chromic acid to heat in close vessels. 

 Oxygen is disengaged, and the green oxide remains 

 behind. 



The deutoxide is intermediate between the green 

 oxide and chromic acid. Its colour is brown. 



The peroxide, or chromic acid, is found native in 

 red lead ore. It is of a red, or orange colour, soluble 

 in water, and composed of one part chromium and 

 two parts oxygen. 



The remaining properties of chromium have not 

 been examined. 



SECT. XXII. Of Uranium. 



Uranium. This metal was discovered by Klaproth, and ex- 

 tracted by him from an ore which occurs in Saxony, 

 and is known by the name of ptchbleiidt. 



Properties 1. It requires so violent a heat to melt it, that 

 hitherto the fusion has only been imperfectly accom- 

 plished. Its colour is iron grey, it has considerable 

 lustre, and is soft enough to yield to the file. Its 

 specific gravity is 9.000. 



Oxide*. 2. It forms various oxides, which have been hither- 



to only examined by Bucholz. 



When heated to redness, it undergoes a species of 

 combustion, and is converted into a greyish black 

 powder, which is the protoxide. It is composed of 

 95 uranium and 5 oxygen. 



When uranium is dissolved in nitric acid, and pre- 

 cipitated by potash, it is obtained in the state of a 

 peroxide. It is a yellow, tasteless powder, insoluble 

 in water. It dissolves with effervescence in muriatic 

 acid, oxymuriatic acid gas being exhaled. It is com- 

 posed of 80 metal and 20 oxygen. 



Besides these two oxides, Bucholz is of opinion, 

 that there are several others intermediate between 

 them, distinguishable by their colour. He recogni- 

 sed four, namely, ihe riulet, the greenish tirotvn, the 

 greyish green, and the orange. 



3. Uranium is capable of uniting with sulphur. 

 No experiments have been made of the action of the 

 other simple combustibles on it. Neither do we 

 know the action of the simple incombustibles, or the 

 alloys which it forms with other metals. 



SECT. XXIII. Of Molybdenum. 



Molybde- This metal is extracted from a scarce mineral call- 



num. ed molybtlrna, first examined by Scheeie. Molybde- 



num was first obtained in the metallic state by Hielm. 



1'roperties. 1. Hitherto it has only been obtained in small 

 grains simply agglutinated. Its colour is silvery 

 white. Its specific gravity is 8.6 11. It is brittle, 

 not altered though kept under water, but the effect 

 of air ii unknown. 



Oxide*. 2. When heated in the open air, it gradually com- 



bines with oxygen, and is volatilized in the form of 



small white needles. It seems capable of forming Elements 

 four different oxides. of 



The protoxide is brown. It is obtained by expo- c 

 sing molybdenum in powder to a red heat. 



By exposing it to a longer and more violent heat, 

 it becomes violet brown. This Bucholz considers as 

 a second oxide. 



The blue oxide may be obtained by carrying the 

 heat a little farther, or by triturating together one 

 part of molybdenum and two parts of molybdic acid, 

 boiling the mass in water, and evaporating the liquid 

 to dryness. This oxide possesses several properties 

 of an acid. It converts vegetable blues to red, and 

 combines with saline bases and forms salts. It may 

 be called molybdons acid. It is composed of 100 

 metal and 34 oxygen. 



The white oxide, or molybdic acid, is obtained by 

 roasting molybdena for some time, dissolving the; 

 grey powder in ammonia, and pouring nitric acid into 

 the solution. The oxide precipitates in fine white 

 scales, which, when melted and sublimed, become 

 yellow. It converts vegetable blues to red, but does 

 not act so powerfully as the blue oxide. It is com- 

 posed of two parts metal and one part oxygen. 



3. Molybdenum combines with phosphorus and 

 sulphur, but not with carbon and hydrogen. 



Sulphuret of .molybdenum occurs native, and is Itfolyb 

 usually called molybdena. It is of a bluish grey co- dena. 

 lour, has the metallic lustre, and is composed of 

 plates. It consists of 60 parts metal and 40 sulphur. 



4. The simple incombustibles do not combine with 

 molybdenum ; but it unites with the metals, and 

 forms alloys which hitherto have been examined only 

 by Hielm. None of them are of much importance. 



SECT. XXIV. Of Tungsten. 



Tungsten was discovered by Scheeie, and reduced Tungsten. 

 to the metallic state by the D'Elhuyars. It is so 

 difficult of fusion, that hitherto it has been very sel- 

 dom procured in a tolerably compact state. It is 

 sometimes called Scheelium, after the discoverer. 



1. It is of a greyish white colour, and has a good Properties. 

 deal of brilliancy. It is very hard, and seems to be 



brittle. Its specific gravity is 17 6'. It requires a 

 temperature at least equal to 17Q Wedge wood to 

 melt it. It is not magnetic. 



2. When heated in an open vessel it is gradually Oxides 

 oxidized. We are acquainted with'' two different 

 oxides of this metal, th<- blue and the yellow. 



The protoxide, or blue oxide, may be obtained by 

 heating the yellow oxide for some hours in a covered 

 crucible. 



The peroxide, or yellow oxide, may be obtained by 

 boiling tungsten, or its ore, in muriatic acid, decant- 

 ing on the acid, and allowing it to settle. A yellow 

 powder gradually precipitates. This yellow powder 

 is to be dissolved in ammonia, the solution evaporated 

 to dryness, and the residue kept for some time in a 

 rtd heat. This yellow oxide is composed of 80 parts 

 metal rnd 20 oxygen. It combines with bases, forms 

 salts, and therefore has been considered as an acid. 

 Its specific gravity is 6.12. 



3. Tungsten combines with sulphur and phospho- 

 rus, but not with hydrogen or carbon, 



