40 ANNUAL OF SCIENTIFIC DISCOVERY. 



water; it is so havcl tliat it scratches iron. It is formed of ninety- 

 three parts of well-l)Urne(l l)riek, anil seven i)arts of litharge, made 

 plastic with linseed oil. Tl>c l^rick and litharge are i)ulverized ; the 

 latter must always l)e reduced to a very line powder; they are 

 mixed together, and enongh of linseed oil atlded. It is then ap- 

 plied in the manner of jjlaster, the body that is to be covered 

 being i)revionsly wet witli a siv.)nge. Tins iK'ccantion is indis- 

 pensalile, otherwise the oil would (ilt<'r through the body and 

 prevent the mastie from acquiring the desired hardness. When 

 it is extended over a large surface, it sometimes happens to have 

 flaws iu it, which must be filled up with a fresh quantity of the 

 cemi-nt. In three or four days it becomes firm. If its advan- 

 tages have not l)een overrated it must be a very excellent cement 

 for making the joints of aquaria water-tight. — Brugijisfs Circular^ 

 1801'.. 



At the meeting of the Paris Academy of the 4th of December, 

 18Go, II. St. Claire Dt'ville showed that magn(!sia, kept for some 

 weeks in pure water, sealed up so that the air is excluded, com- 

 bines with water, and forms a hard and comjjact, crystalline, 

 translucent suljstanee, consisting of magnesia GS.S, water oi.7, or 

 a simple hydratt! of magnesia. lie lias made copies of medals, 

 like those of plaster, from magnesia thus hardened under water. 

 Balard's magnesia, calcined at a red heat, he says, has hydraidie 

 qualities whicli are manifested with a rapidity that is admirable, 

 though, when calcined at a white heat, tins property is almost en- 

 tirely lost. A mixture of powdered chalk, or marble and magne- 

 sia in equal parts, furnishes with water a ])aste which is slightly 

 l)lastic, but which, after being some time in water, affords prod- 

 ucts of very great solidity; and he pnjposes to make busts of arti- 

 ficial marble i'rom the mixture. Plaster mixed with the magne- 

 sia diminishes the hydraulic ])roperties. On calcining dolomites 

 rich in magnesia, the same rule as to hydraulic j)roperties is I'c- 

 marked iu regard to tempt'rature, the higher the heat the less the 

 hydraulic projierties. lie thus believes that this suljstance, now 

 so cheaj^ly and abundantly furnished by M. Balard's processes, 

 will come into extensive use in subaqueous structures. — Les 

 Maudes, Bee. 7, IBGo. 



A cement, capable of uniting into a solid mass stones, jDebbles, 

 &c.,so as to form artificial pudding-stone, conglomerates, &c., of 

 extraordinary strength and tenacit\% impervious to moisture, and 

 capable of being moulded into statues, bas reliefs, &c., ma}'^ be 

 made by finely triturating iron sponge, and mixing it with sand 

 which has been moistened with slightly acidulated water. The 

 iron is oxidiziid at the expense of the water, and the silex forms 

 with the oxide silicate of iron, which possesses a very great 

 tenacity, and is not affected by atmospheric changes, nor even by 

 acid or alkaline liquids at a boiling temiDeraturc. — Intelleclual 

 Observer, Feb., ISGG. 



CEMENT WITU A GYPSUM BASIS. 



The plaster is first burned in the usual way, in an ai^iirojiriate 

 fui-uace, to diive off the water ; after this it is broken into small 



