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all ages been associated with beauty and riches is nothing but the 

 brilliant sarcophagus of a worm." From the shells of the pearl- 

 oyster comes the substance known as mother of pearl. The north 

 and north-west of Australia and the Straits Settlements are among 

 the localities from which European supplies come. The annual 

 value of that imported into England amounts to ^"300,000 or so, 

 and many persons find employment in working in this material. 

 It is used for inlaid-work of various kinds, for cutlery handles, 

 buttons and many other such purposes. 



Thus far we have been dealing with the uses of various 

 forms of Calcium Carbonate dependent upon physical and 

 mechanical properties. Thus the hardness of marble is neither 

 too great nor too small for the purposes of the sculptor, purposes 

 for which its evenness of texture and capability of taking a high 

 polish further adapt it. The softness and whiteness of chalk are 

 the properties upon which most of the uses already mentioned 

 depend. Bath-stone and other calcareous building-stones are 

 easily quarried and worked into shape and harden by exposure, 

 coral and pearl are fitted by colour in the one case and iridescent 

 lustre in the other for purposes of personal adornment. But there 

 are equally numerous uses dependent upon chemical properties. 

 When any form of Calcium Carbonate is heated to a sufficiently 

 high temperature it is split up into two substances. One of these 

 is lime, a white or whitish solid, the other an invisible gas, carbon 

 dioxide. In the first lecture of the course the process of lime-burn- 

 ing and the use of lime in making mortar were described. Refer- 

 ence was also made to hydraulic mortars and to cements. There 

 is a kind of loosely coherent volcanic sand found at Pozzuoli, near 

 Naples, which gives a good hydraulic mortar when mixed with 

 ordinary lime. Roman cement is made from a peculiar kind of 

 impure limestone containing a certain proportion of clay and 

 known as cement-stone. This is burnt in kilns, then ground, 

 sifted and mixed with sand. Portland cement is made from chalk 

 mixed with the clayey mud of the Thames and Medway. These 

 are ground with water to a creamy consistence and the cream 

 allowed to stand for a few weeks in reservoirs. The excess of 

 water is drawn off and the mixture dried, burnt in kilns and finally 

 ground to powder. This is the wet process, but this cement is also 

 made by a dry process from other kinds of limestone than chalk 

 and other kinds of clay. The cement is generally mixed with sand 

 and gravel or broken stones. It has great strength, whilst its 

 power of hardening under water renders it useful for dock work, 

 breakwaters and the like. 



A mass of stones, sand, gravel, etc., held together with 

 cement or ordinary mortar is known as concrete. 



The use of lime in building is immense. Limestone from the 

 quarries is used in certain districts for building purposes and the 

 finer varieties are carried to distant places for facing or otherwise 

 ornamenting houses and other buildings constructed in the main 

 of other materials. Only a few persons, except in Dreamland, 



