'204 ANNUAL OF SCIENTIFIC DISCOVERY. 



ARTIFICIAL STONE. 



The following is an abstract of a paper on the above subject, com- 

 municated to the British Association, in 1862, by Prof. Anstead : 

 My object in the present communication is to direct the attention of 

 the section to the different classes of the material that have been 

 found available ; to point out the principles involved in each, and the 

 special advantage and disadvantage each possesses ; to refer to a new 

 and I believe an important material ; and to suggest the bearing of 

 the whole subject on that of the preservation of stone from decay. 



The artificial stones hitherto used may be grouped under one 

 of three heads. They are either (1) terra cotta, or manufactures 

 of plastic clay burnt in a kiln ; (2) cements manufactured from a 

 certain kind of limestone containing foreign ingredients of such a 

 nature, that, when converted into lime by burning, the lime thus made 

 possesses the property of setting very rapidly and firmly when wet- 

 ted ; (3) silicious stone, obtained by burning in a kiln, sand, and other 

 substances, moulded with a solution of silicate of soda, which is con- 

 verted into a kind of glass, firmly connecting the particles. I omit 

 plasters, as rarely exposed to the weather. 



Terra Cotta. The advantages of this material are, (1) its cheap- 

 ness and the universal distribution of the clavs of which it can be 



ft 



made ; (2) the facility with which it can be moulded to any required 

 form ; and (3) the pleasant color of the material when uninjured by 

 long exposure to weather. The disadvantages of terra cotta are, (1) 

 the uncertainty of the result, owing to the great and unequal con- 

 traction of all clays in burning ; (2) its want of power to resist damp 

 and frost whenever there is the slightest flaw, whether produced be- 

 fore or after burning ; (3) its brittleness and want of strength ; (4) 

 its exposure to a disagreeable green vegetation in damp air after a 

 few years' weathering. Terra cottas are better adapted to a dry than 

 a moist climate. 



Cement. Whether of the kind called Pozzuolana, Roman, or Par- 

 ker's, or Atkinson's, or any modification of these, all the cements are 

 similar in their nature. The advantages of cements used as an artificial 

 stone are, (1) its cheapness when made, and its ready transport; (2) 

 its not requiring the kiln, but setting at once without contraction ; 



(3) the facility of moulding, and in making up the material from the 

 manufactured cement supplied ; (4) its great strength when well 

 made. The disadvantages are, (1) that it cracks and peels badly 

 when exposed to frost and damp air; (2) that it is very irregular, 

 some samples yielding a much harder, better, and more lasting stone 

 than others, without apparent reason ; (3) that it is subject to a green 

 vegetation, like terra cotta. These disadvantages do not all apply to 

 its use in making concrete, for which it is admirably adapted. 



Silicious Stone. This product, known in England as Ransonie's, 

 is extensively used. The advantages are, (1) the extreme uniformity 

 of its texture ; (2) the almost entire absence of contraction, and its 

 freedom from cracks and flaws produced during burning ; (3) its com- 

 plete, resistance to all kinds of weathering, to which may be added 



( 4) its pleasing color and tint. 



On the other hand, among the disadvantages are, (1) its cost, which 



