570 CESIUM 



CADMIUM. (Symbol, Cd. ; Atomic weight, 56.) A metal discovered by Stro- 

 meyer about the beginning of the year 1818. It derives the name Cadmium from 

 Cadmia fossilis a denomination by which the common ores of zinc were formerly dis- 

 tinguished. It occurs chiefly in Silesia in several ores of zinc, and may be readily 

 recognised by means of the blowpipe ; for, at the first impression of the reducing 

 or smoky part of the flame, the ores containing cadmium stain the charcoal all round 

 them with a reddish-yellow circle of oxide of cadmium. The Silesian native oxide 

 of zinc contains from 1J to 11 per cent of cadmium. The only native compound of 

 cadmium is the sulphide called Greenockite. See GEEENOCKITE. 



Cadmium may be extracted by dissolving the ores containing it in sulphuric acid, 

 leaving the solution acidulous, and diluting it with water, then transmitting through 

 it a stream of sulphuretted hydrogen, till the yellow precipitate ceases to fall. The 

 powder, which is sulphide of cadmium, is to be dissolved in concentrated muriatic 

 acid, the excess of which is to be expelled by evaporation ; and the salt being dis- 

 solved in water, carbonate of ammonia is added in excess ; cadmium separates as a 

 carbonate, while the adhering copper or zinc is retained in solution by the ammonia. 

 Ilorapath has shown that, in distilling zinc per descensum, the first portions of 

 gaseous metal which are disengaged burn with a brown flame and deposit the brown 

 oxide of cadmium. See ZINC. 



Cadmium has the colour and lustre of tin, and is susceptible of a fine polish. Its 

 fracture is fibrous ; it crystallises readily in regular octahedrons : and when it sud- 

 denly solidifies, its surface gets covered with fine mossy vegetations. It is soft, easily 

 bent, filed, and cut, soils like lead any surface rubbed with it. It is harder and more 

 tenacious than tin, and emits a creaking sound when bent, like that metal. It is very 

 ductile, and may be drawn out in fine wire, and hammered into thin leaves, without 

 cracking at the edges. Its specific gravity, after being merely melted, is 8-604 ; and 

 8'6944 after it has been hammered. It is very fusible, melting at a heat much under 

 redness ; indeed, at a temperature little exceeding that of boiling mercury, it boils and 

 distils over in drops. Its vapours have no smell. It is but slightly altered by expo- 

 sure to air. When heated in the atmosphere it readily takes fire and burns with a 

 brownish-yellow smoke, which is destitute of smell. In strong acids it dissolves with 

 disengagement of hydrogen, and forms colourless solutions. Chromate of potash 

 causes no precipitate in them, unless zinc or lead be present. 



There are two oxides of cadmium: a suboxide Cd 2 and a protoxide CdO. The 

 protoxide is a brown powder obtained by igniting the metal, or by heating its carbonate 

 or nitrate. It is neither fusible nor volatile at a very high temperature. When in 

 the state of a hydrate, it is white. This oxide of cadmium consists of 87'45 parts of 

 metal and 12'55 oxygen, in 100 parts. The other, or suboxide of cadmium, is ob- 

 tained by heating the oxalate of cadmium to about the melting point of lead. It is 

 a green powder resembling oxide of chromium. 



CADMIUM, ALLOYS OF. One hundred parts of copper at a red heat 

 combine with eighty-two parts of cadmium. This alloy is of a yellowish-white colour. 

 Platinum at a red heat will take up 117 parts of cadmium. This alloy is silver white, 

 very brittle, and refractory in the fire. With mercury, cadmium forms a hard, brittle, 

 white amalgam. These alloys have no commercial value or manufacturing interest. 



Some of the alloys of cadmium are remarkable for their fusibility ; thus, an alloy 

 of 1 part cadmium, 6 parts of lead, and 7 of bismuth melts at 180 1\, or considerably 

 below the temperature of boiling water. Alloys containing cadmium have been used 

 for stopping teeth. 



CADMIUM, SALTS OF. Bromide, chloride, iodide, and sulphate of cadmium 

 have been prepared and examined, but with the exception of the use of the bromide 

 and iodide in photography, none of these salts are of any importance in the arts. 

 The sulphate has been applied to the eyes by surgeons to remove specks on the cornea. 

 See Watts's ' Dictionary of Chemistry.' 



CADMIUM YELLOW or CADMIUM! SULPHIDE. The artificial sulphide 

 of cadmium is prepared by fusing cadmium with sulphur, by igniting cadmic oxide 

 (protoxide of cadmium) with sulphur, or it is precipitated in yellow flakes, as a 

 hydrate, when sulphuretted hydrogen or an alkaline hydrosulphate is brought in contact 

 with a cadmium salt. This forms the pigment cadmium yellow, oijaune brttlant. Tho 

 sulphide occurs native as Greenockite. See GBEENOCKITE. 



CAEN STONE. A variety of Oolitic limestone, which is largely quarried at 

 Caen in Normandy, and which has been used for a long period in Gothic churches and 

 other buildings. See OOLITIC LIMESTONE. 



CJCK.ui.EUM. A blue pigment, consisting of stannate of protoxide of cobalt, 

 mixed with stannic acid and sulphate of lime. 



C-ZSIUM. (Symbol, Cs. ; Atomic weight, 133.) One of the new metals discovered 

 by aid of the spectrum analysis in 1860 by Kirchoff and Bunsen. It has not been 



