Chemical elements
    Physical Properties
    Chemical Properties
      Calcium Hydride
      Calcium Subfluoride
      Calcium Fluoride
      Calcium Subchloride
      Calcium Chloride
      Calcium Bromide
      Calcium Subiodide
      Calcium Iodide
      Calcium Periodides
      Calcium Halides
      Calcium Perhalides
      Calcium Oxychloride
      Calcium Hypochlorite
      Bleaching Powder
      Calcium Chlorite
      Calcium Chlorate
      Calcium Perchlorate
      Calcium Oxybromide
      Calcium Hypobromite
      Brome Bleaching Powder
      Calcium Bromate
      Calcium Oxyiodide
      Calcium Hypoiodite
      Iodine Bleaching Powder
      Calcium Iodate
      Calcium Periodate
      Calcium Manganites
      Calcium Manganate
      Calcium Permanganate
      Calcium Oxide
      Caustic lime
      Calcium Suboxide
      Calcium Hydroxide
      Calcium Peroxide
      Calcium Peroxyhydrates
      Calcium Tetroxide
      Calcium Monosulphide
      Calcium Hydrosulphide
      Calcium Polysulphides
      Calcium Hydroxyhydrosulphide
      Calcium Oxysulphides
      Calcium Thiosulphate
      Calcium Hyposulphite
      Calcium Sulphite
      Calcium Bisulphite
      Calcium Sulphite
      Calcium Dithionate
      Calcium Trithionate
      Calcium Sulphate
      Acid Calcium Sulphates
      Calcium Pyrosulphate
      Calcium Selenide
      Calcium Selenite
      Calcium Selenate
      Calcium Telluride
      Calcium Tellurite
      Calcium Tellurate
      Calcium Chromite
      Calcium Chromate
      Calcium Dichromate
      Calcium Tetrachromate
      Basic Calcium Chromate
      Calcium Chlorochromate
      Calcium Molybdate
      Calcium Tungstate
      Calcium Uranate
      Calcium Peruranate
      Calcium Nitride
      Calcium Azide
      Calcium Hexammoniate
      Calcium Ammonium
      Calcium Amide
      Calcium Imide
      Calcium Hydroxylamite
      Calcium Imidosulphonate
      Calcium Hyponitrite
      Calcium Nitrohydroxylaminate
      Calcium Nitrite
      Calcium Nitrate
      Basic Calcium Nitrates
      Calcium Phosphide
      Calcium Dihydrohypophosphite
      Calcium Hydrophosphite
      Neutral Calcium Phosphite
      Calcium Dihydrophosphite
      Acid Calcium Phosphite
      Neutral Calcium Hypophosphate
      Acid Calcium Hypophosphate
      Calcium Orthophosphates
      Calcium Pyro- Meta-phosphates
      Calcium Ultraphosphates
      Calcium Selenophosphate
      Basic Calcium Phosphates
      Phosphatic Fertilisers
      Calcium Arsenide
      Calcium Arsenites
      Calcium Arsenates
      Calcium Pyroarsenate
      Calcium Thioarsenites
      Calcium Thio-oxyarsenate
      Calcium Antimonide
      Calcium Antimonate
      Calcium Orthovanadate
      Calcium Pyrovanadate
      Calcium Metavanadate
      Calcium Pervanadate
      Calcium Pyro- Meta- niobates
      Calcium Pyro- Meta-tantalate
      Calcium Potassium Pertantalate
      Calcium Carbide
      Calcium Formate
      Calcium Acetate
      Calcium Oxalate
      Calcium Carbonate
      Calcium Bicarbonate
      Calcium Trithiocarbonate
      Calcium Perthiocarbonate
      Calcium Cyanide
      Calcium Oxycyanide
      Calcium Cyanamide
      Calcium Cyanate
      Calcium Cyanurate
      Calcium Thiocyanate
      Calcium Silicide
      Calcium Monosilicide
      Calcium Silicalcyanide
      Monocalcium Silicate
      Calcium Meta-silicate
      Calcium Orthosilicate
      Dicalcium Silicate
      Tricalcium Silicate
      Acid Calcium Silicate
      Calcium Fluosilicate
      Calcium Aluminates
      Monocalcium Aluminate
      Tricalcium Aluminate
      Pentacalcium Aluminate
      Calcium Stannate
      Calcium Chlorostannate
      Calcium Silicostannate
      Calcium Orthoplumbate
      Calcium Metaplumbate
      Acid Calcium Plumbate
      Calcium Metatitanate
      Calcium Fluotitanate
      Calcium Silicotitanate
      Calcium Zirconate
      Calcium Silicozirconate
      Calcium Boride
      Calcium Borates
      Calcium Silicoborate
      Calcium Borostannate
      Calcium Perborate
      Calcium Ferrate
    PDB 158d-1ajq
    PDB 1ak9-1ayk
    PDB 1ayo-1bg7
    PDB 1bg9-1byh
    PDB 1byn-1c8q
    PDB 1c8t-1cq1
    PDB 1cq9-1daq
    PDB 1dav-1dva
    PDB 1dvi-1el1
    PDB 1ela-1f4n
    PDB 1f4o-1fkq
    PDB 1fkv-1fzd
    PDB 1fze-1g9i
    PDB 1g9j-1gr3
    PDB 1gsl-1h5h
    PDB 1h5i-1hn4
    PDB 1hny-1i9z
    PDB 1ia6-1iyi
    PDB 1iz7-1jc2
    PDB 1jc9-1jui
    PDB 1jv2-1kck
    PDB 1kcl-1kvx
    PDB 1kvy-1led
    PDB 1lem-1lqd
    PDB 1lqe-1may
    PDB 1mbq-1mxe
    PDB 1mxg-1nfy
    PDB 1ng0-1nwg
    PDB 1nwk-1o3g
    PDB 1o3h-1om7
    PDB 1om8-1p7v
    PDB 1p7w-1pva
    PDB 1pvb-1qdo
    PDB 1qdt-1qq9
    PDB 1qqj-1rin
    PDB 1rio-1s10
    PDB 1s18-1scv
    PDB 1sdd-1su4
    PDB 1sub-1tf4
    PDB 1tf8-1top
    PDB 1tpa-1ujb
    PDB 1ujc-1uyy
    PDB 1uyz-1v73
    PDB 1v7v-1w2k
    PDB 1w2m-1wua
    PDB 1wun-1xkv
    PDB 1xmf-1y3x
    PDB 1y3y-1yqr
    PDB 1yr5-1zde
    PDB 1zdp-2a3x
    PDB 2a3y-2arb
    PDB 2are-2bd2
    PDB 2bd3-2bu4
    PDB 2bue-2c6g
    PDB 2c6p-2cy6
    PDB 2cyf-2dso
    PDB 2dtw-2eab
    PDB 2eac-2fe1
    PDB 2ff1-2fwn
    PDB 2fws-2gjp
    PDB 2gjr-2hd9
    PDB 2hes-2i6o
    PDB 2i7a-2ivz
    PDB 2iwa-2j7g
    PDB 2j7h-2jke
    PDB 2jkh-2kuh
    PDB 2kxv-2o1k
    PDB 2o39-2ovz
    PDB 2ow0-2pf2
    PDB 2pfj-2pyz
    PDB 2pz0-2qu1
    PDB 2qua-2re1
    PDB 2rex-2tmv
    PDB 2tn4-2vcb
    PDB 2vcc-2vqy
    PDB 2vr0-2w3i
    PDB 2w3j-2wlj
    PDB 2wm4-2wzs
    PDB 2x0g-2xmr
    PDB 2xn5-2z2z
    PDB 2z30-2zn9
    PDB 2zni-3a51
    PDB 3a5l-3ahw
    PDB 3ai7-3bcf
    PDB 3bdc-3bx1
    PDB 3bxi-3ch2
    PDB 3chj-3d34
    PDB 3d3i-3djl
    PDB 3dng-3e4q
    PDB 3e5s-3eqf
    PDB 3eqg-3faq
    PDB 3faw-3fou
    PDB 3foz-3gci
    PDB 3gcj-3gwz
    PDB 3gxo-3hjr
    PDB 3hkr-3i4i
    PDB 3i4p-3io6
    PDB 3ior-3k5m
    PDB 3k5s-3kqa
    PDB 3kqf-3lei
    PDB 3lek-3lum
    PDB 3lun-3mip
    PDB 3mis-3n7b
    PDB 3n7x-3nvn
    PDB 3nx7-3owf
    PDB 3ox5-3prq
    PDB 3prr-3sg5
    PDB 3sg6-3u39
    PDB 3u43-3vpp
    PDB 3zqx-4awy
    PDB 4awz-4dtu
    PDB 4dtx-4eoa
    PDB 4epz-5apr
    PDB 5bca-8tln
    PDB 966c-9rnt

Calcium Monosulphide, CaS

Calcium sulphide has been found in the natural state in a meteorite fallen in India. It may be prepared by any of the following methods: -
  1. The action of sulphuretted hydrogen on calcium carbonate or sulphate at red heat.
  2. The action of sulphuretted hydrogen on calcium hydroxide. The reaction begins at 60° C. Anhydrous calcium oxide does not absorb the dry gas at low temperatures, but at red heat gives the sulphide.
  3. The reduction of calcium sulphate by carbon, moist hydrogen, water gas, carbon monoxide, or sulphur. This method is the most convenient technically, especially the reduction by carbon.
  4. The action of sulphur on calcium carbonate, and on anhydrous calcium oxide at red heat in a current of hydrogen.
  5. The action of sodium sulphide on calcium carbonate at red heat.
  6. The action of carbon bisulphide on quicklime at high temperatures. The last method produces the purest sulphide.

Pure calcium sulphide is white, but the commercial product is generally coloured yellow, or yellowish red, by impurities in the original materials. It is usually obtained as an amorphous powder of density 2.25, but by fusion in the electric furnace, or by preparation through reduction of the sulphate by carbon in the electric furnace, brilliant cubical crystals of density 2.8 at 15° C. are produced.

The molecular heat of formation from the metal and solid sulphur is 94.3 Cal., from gaseous sulphur 114.82 Cal.

Calcium sulphide is stable in air, and more readily fusible at high temperatures than the corresponding strontium and barium compounds.

It is only slightly soluble in water, 0.212 grm. dissolving in one litre at 20° C., but it is readily hydrolysed with the formation of the more soluble products calcium hydroxide and hydrosulphide. The crystalline sulphide is more readily attacked than the amorphous compound. The molecular heat of solution is 6.3 Cal. The solubility is greatly increased by the presence of sulphuretted hydrogen through the formation of hydrosulphide. At 20° C., and under a pressure of gas of 760 mm., the solubility calculated as sulphide is 206.5 grm. per litre. This affords a means of purifying calcium sulphide by extracting the crude material with sulphuretted hydrogen solution under pressure in absence of air, and then precipitating pure calcium sulphide by removing the gas from the solution at low pressures.

Calcium sulphide is a by-product of the Le Blanc process, and is treated for the recovery of sulphur.

Phosphorescent Calcium Sulphide

Calcium, sulphide as usually prepared - that is, containing a certain amount of impurity - phosphoresces after exposure to a bright light or some other exciting agent, such as cathode rays. It was used in very early times in Bacchanalian rites, and later became known as Canton's phosphorus. The pure compound does not possess this property, which is apparently associated with the presence of minute quantities of certain heavy metals, notably bismuth, copper, manganese, nickel, vanadium, tungsten, molybdenum, and the rare earths. The nature of the impurity affects the colour of the phosphorescence, and the quantity influences the intensity, an optimum value being found. The presence of a little alkali sulphate or carbonate is apparently also necessary.

According to Waentig, phosphorescence is conditioned by the presence of the heavy metal, or phosphorogen, in the form of a solid solution, the intensity increasing so long as the solution is homogeneous. This would explain the existence of a maximum value with increasing quantity of the heavy metal. The solubility is very small, but increases with temperature, so that the phosphorescent sulphides are supersaturated solutions - temperature, duration of heating, and rate of cooling being important factors in their preparation. The presence of a fusible alkali salt is favourable, because it aids the solution of the phosphorogen and hinders its separation during cooling.

Vanino and Zumbusch made a careful study of the factors influencing the phosphorescing power of calcium sulphide or Bolognian stones. They drew the following conclusions: The most favourable quantity of bismuth for example, as phosphorogen, is of the order of 0.000135 grm. per grm. of sulphide. An alkali salt of low melting- point is better than one of high, and it is possible to use too large a quantity, 2 per cent, of lithium carbonate, for instance, is better than 12 per cent. The physical structure of the lime used for preparing the sulphide (by heating with sulphur) influences the final product. For example, the oxide from the hydroxide or carbonate is better than that from the nitrate - it probably influences the amount of polysulphide. A mixture of the alkaline earths gives a more intense phosphorescence than any one alone. The proportion of sulphur may vary between 12 and 33 per cent., but with more the luminosity is considerably diminished. The texture of the sulphide is important, if hard and stony it is non-luminous. There is no connection between colour photo-sensitiveness and phosphorescing power. Finally, the presence of a reducing agent, for example 4 per cent, starch, is advantageous, although larger quantities may completely destroy the phosphorescence.

Mourelo observed that some specimens of calcium sulphide change colour under the influence of light and that, although the phosphorogen is also the phototrope, this phototropic property is apparently independent of the phosphorescing power of the compound. The change in colour is confined to the surface exposed to light, and no regularity can be observed between the colour assumed and the composition. The intensity of phototropy increases as the percentage of phosphorogen diminishes from 0.1 to 0.0001, but beyond this it decreases and soon disappears.

Lenard and Saeland regard photo-electric action as intimately connected with the phosphorescence of sulphides and as localised in certain centres which are also centres of light emission. Excitation by light or cathode rays consists in the loss of an electron from an atom of the foreign metal, and the resulting phosphorescence is due to the recombination of the metal with electrons. In this connection Perrin's view is interesting. He considers that chemical reaction takes place under the influence of the exciting rays, and that this is reversed in the dark with the emission of energy as phosphorescent radiation.

The electrical conductivity of calcium sulphide is affected by exposure to light, and there appears to be a connection between conductivity and phosphorescence.

Observations on phosphorescence spectra at temperatures down to -259° C. show that the bands become sharper and narrower as the temperature falls, and that different bands belong to different temperature ranges.
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