248 REPORT— 1872. 



The system of clarifying the sewage most strongly recommencled by his experi- 

 ence was that of allowing it to settle by simple subsidence ; the sludge is then 

 recommended to be used by itself in a solid state. 



On some Recent Improvements in tJie Manufacture of Artificial Stone, and the 

 Application of such Stone to Constructive and other Purposes. By Feedeeick 

 Eansome, A.I.O.E, 



The progressive development of the natural world, through periods which 

 occurred long before the dawn of the most remote traditions of antiquity, has 

 placed at the disposal of man materials which for the most part eminently 

 subserve the varied purposes of construction and decoration. These materials, 

 however, such as the granites, marbles, sandstones, limestones, &c., occur in 

 isolated groups, in some instances so remote from the centres of civilization as to 

 render the employment of them prohibitable for general use, excepting in local 

 situations. The requirements of man at an early period of his history demanded 

 a material which should approximately fulfil the conditions of stone ; and this 

 necessity was in the earlier ages supplied by the manufacture of bricks, concrete, 

 &c. The advantages attbrded by these substances were readily recognized by the 

 ancients, and have been fully appreciated in modern times ; but great as these 

 advantages are in a constructive point of view, they fall very far short of the 

 requirements of the present age. 



It is therefore no matter for surprise that numerous attempts have been made, 

 from time to time, to supersede the productions of nature by the imitations of art ; 

 and the importance of producing a material combining all the advanlages, without 

 having the defects, of the most useful building-stones, and jiossibly possessing 

 attributes peculiarly and specifically its own, was recofjiiized many years since by 

 the author, who set himself the task of solving the problem of manufacturing an 

 artificial stone which should economically answer the varied purposes of the pro- 

 ductions of nature. 



His investigations into the nature and properties of stone commenced nearly 

 thirty years since, and he found that, with few exceptions, the hardest and most 

 durable stones were those which contained the largest proportion of silica. 



Many geologists will doubtless recollect that some years since a siliceous 

 mineral was discovered at the base of the chalk hills in Surrey (especially in the 

 neighbourhood of Farnham) possessing some very peculiar properties, amongst 

 others that of being readily soluble in a solution of caustic soda, at a moderately 

 low temperature. Taking advantage of this peculiarity, the author commenced a 

 series of experiments, in order to determine if it were not possible, without the use 

 of chloride of calcium, to produce a stone in all respects equal in quality to what 

 had hitherto been done ; and in this he has now succeeded. 



By this latter process he combines a portion of the Farnham stone, or soluble 

 silica, with a solution of silicate of soda or potash, lime (or substances containing 

 lime), sand, alumina, chalk, or other convenient and suitable materials, which, 

 when intimately mixed, are moulded into the required form as heretofore, and 

 allowed to harden gradually, as silicate of lime is formed by the combination of 

 the ingredients present. The mass then becomes thoroughly indurated and con- 

 verted into a compact stone, capable of sustaining extraordinary pressure, and in- 

 creasing in hardness with age. 



The chemical actions which effect these results appear to be as under. When 

 the materials are mixed together, the silicate of soda is decomposed, the silicic 

 acid being liberated combines with the lime and forms a compound silicate of lime 

 and alumina, while a portion of soda in a caustic condition is set free. This 

 caustic soda immediately seizes upon the soluble silica (from Farnham), which 

 constitutes one of the ingredients, and thus forms a fresh supply of silicate of 

 soda, which is in its turn decomposed by a further quantity of lime, and so on. 



If each decomposition of silicate of soda resulted in the setting free of the whole 

 of the caustic soda, these decomposing processes would go on as long as there was 

 any soluble silica present with which the caustic soda could combine, or until 



