494 CALCIUM. 



as common mortar, or in covering buildings to imitate stone. 

 From the minute division of the silica and alumina in this 

 mortar, their combination with lime is more likely to occur 

 than in ordinary mortar. Still the first setting of hydraulic mor- 

 tar seems to be due simply to the fixation of water, and forma- 

 tion of a solid hydrate like gypsum. Hydraulic mortar is 

 sometimes made by mixing together clay and chalk, and cal- 

 cining the i mixture, or more frequently by adding to hydrate 

 of lime puzzolano ground to fine powder. The latter is a sub- 

 stance of volcanic origin, composed principally of pumice, of 

 which a stratum is excavated in the neighbourhood of Pozzuoli 

 near Naples. The mortar which it makes with lime has ob- 

 tained the name of Roman cement. 



The hydrate of peroxide of calcium precipitates on adding 

 lime-water, drop by drop, to a solution of peroxide of hydrogen. 

 It contains, according to Thenard, 2 eq. of oxygen. 



The proto sulphur et of calcium is procured by decomposing 

 sulphate of lime at a red heat, by hydrogen or charcoal. When 

 newly prepared, it phosphoresces in the dark. It is sparingly 

 soluble in water. When hydrate of lime is boiled with sulphur 

 and water, and the liquor allowed to cool before it is com- 

 pletely saturated with sulphur, yellow crystals separate from it, 

 which are a bisulphuret of calcium, combined with 3 HO, ac- 

 cording to the observations of Herschel. W r hen lime, or pro- 

 tosulphuret of calcium is boiled with excess of sulphur, it 

 dissolves sulphur till a pentasulphuret of calcium is formed, which 

 resembles in properties the corresponding degree of sulphuratiori 

 of potassium. 



Phosphuret of calcium Small fragments of quicklime being 

 heated to redness, by a spirit lamp, in a small, mattrass with a 

 long neck, and fragments of phosphorus dropt into the same 

 vessel, a mixture is obtained of phosphate of lime and phos- 

 phuret of calcium. The compound has a chocolate brown 

 colour. When the temperature is raised too high, the affinities 

 change, and phosphorus escaping in vapour, nothing but lime 

 remains. This substance decomposes water, when thrown into 

 it, with effervescence, from the escape of phosphuretted hy- 

 drogen, which takes fire spontaneously, while hypophosphite 

 of lime is dissolved by the water. 



Chloride of calcium ; Ca Cl ; 698.7, or 55.98. Obtained by 

 neutralising hydrochloric acid with carbonate of lime, or as a 



