Cadmium sulfide is the inorganic compound with the formula CdS. Cadmium sulfide is a yellow solid. It occurs in nature with two different crystal structures as the rare minerals greenockite and hawleyite, but is more prevalent as an impurity substituent in the similarly structured zinc ores sphalerite and wurtzite, which are the major economic sources of cadmium. As a compound that is easy to isolate and purify, it is the principal source of cadmium for all commercial applications. Its vivid yellow color led to its adoption as a pigment for the yellow paint "cadmium yellow" in the 18th century. Production Cadmium sulfide can be prepared by the precipitation from soluble cadmium(II) salts with sulfide ion. This reaction has been used for gravimetric analysis and qualitative inorganic analysis.The preparative route and the subsequent treatment of the product, affects the polymorphic form that is produced (i.e., cubic vs hexagonal). It has been asserted that chemical precipitation methods result in the cubic zincblende form. Pigment production usually involves the precipitation of CdS, the washing of the solid precipitate to remove soluble cadmium salts followed by calcination (roasting) to convert it to the hexagonal form followed by milling to produce a powder. When cadmium sulfide selenides are required the CdSe is co-precipitated with CdS and the cadmium sulfoselenide is created during the calcination step. Cadmium sulfide is sometimes associated with sulfate reducing bacteria. Routes to thin films of CdS Special methods are used to produce films of CdS as components in some photoresistors and solar cells. In the chemical bath deposition method, thin films of CdS have been prepared using thiourea as the source of sulfide anions and an ammonium buffer solution to control pH: Cd2+ + H2O + (NH2)2CS + 2 NH3 → CdS + (NH2)2CO + 2 NH4+ Cadmium sulfide can be produced using metalorganic vapour phase epitaxy and MOCVD techniques by the reaction of dimethylcadmium with diethyl sulfide: Cd(CH3)2 + Et2S → CdS + CH3CH3 + C4H10 Other methods to produce films of CdS include Sol–gel techniques Sputtering Electrochemical deposition Spraying with precursor cadmium salt, sulfur compound and dopant Screen printing using a slurry containing dispersed CdS Reactions Cadmium sulfide can be dissolved in acids. CdS + 2 HCl → CdCl2 + H2S When solutions of sulfide containing dispersed CdS particles are irradiated with light, hydrogen gas is generated: H2S → H2 + S ΔHf = +9.4 kcal/mol The proposed mechanism