CALCIUM CARBONATE 207 



chalk is obtained by the interaction of calcium chloride 

 and sodium carbonate. It is a dull-white, micro-crystalline, 

 tasteless powder, adheres to the tongue, owing to its porosity 

 and its affinity for water, and effervesces with acids. Calcium 

 carbonate is a constituent of the bones of animals, of shells, 

 and of corals. It is the common source of hardness in drink- 

 ing water, which, when pure, holds about two grains dissolved 

 in the gallon ; but carbonic acid increases the solvent power 

 of the water. Sixteen grains are sometimes taken up, and 

 in chalk districts much more ; but when such hard waters 

 are boiled, the carbonic anhydride is driven off, and calcium 

 carbonate is deposited in the kettles and boilers. 



ACTIONS AND USES. Chalk is a cheap and convenient 

 antacid, much used for the domesticated animals in the 

 treatment of indigestion and chronic diarrhoea. It resembles 

 lime, but is less irritant, and its effects extend beyond the 

 stomach, throughout the intestines, neutralising acidity, and 

 leaving a protecting film of carbonate, thus acting much in 

 the same way as the bismuth salts. It is an antidote for 

 oxalic, carbolic, and the mineral acids. In a dry and finely- 

 divided state it is used as a desiccant and astringent for 

 abraded skin surfaces, burns and ulcers. 



DOSES, etc. For horses, i. to ij. ; for cattle, ij. to 

 iv. ; for sheep, 3ij. to 3iv. ; for pigs, 3i. to 3ij. ; for dogs, 

 grs. viij. to grs. xxx. It is conveniently given in bolus, or 

 suspended in milk, gruel, or mucilage. When administered 

 in large or frequently-repeated doses the bowels should be 

 kept open, in order to prevent its accumulation in the in- 

 testines. It is frequently conjoined with catechu, kino, and 

 other vegetable astringents to arrest excessive discharges ; 

 with ginger and other carminatives, to control indigestion 

 and diarrhoea ; with opium or belladonna, to diminish 

 irritability or pain ; and with salicylic acid, or bismuth, in 

 diarrhoea and hsemorrhagic gastritis in dogs. The following 

 formulae prove serviceable as antacids, carminatives, and mild 

 astringents: For horses, half an ounce each of chalk, 

 gentian, and ginger is made up in the usual way with linseed 

 meal and treacle, or with glycerin ; or chalk i., opium 3i, 

 and creosote TT\x., are made into bolus ; or again, half an 

 ounce each of chalk, catechu, and ginger are conjoined with 



