590 



FARMERS' REGISTER. 



[No. 10 



on its surface. ' This will happen in warm dry 

 weather in five or six hours, but in moist weather, 

 some days may elapse belbre the cement acquires 

 a pro|)er degree of consistence, l^lie mass is tlien 

 broken up by the pickaxe, and intimately mixed 

 lor the second time by ao-itation. No water need 

 be added to the mass, but it will regain ils fluidity 

 by stirring. When the water in which the struc- 

 ture is to be built is deep, the mixture is plunged 

 info it by mens of a wooden case of cubical pha[)e. 

 This is managed l^y means of a windlass mo\'ea- 

 bie lipon a rail road, and has a sliding bottom, or 

 a shutter fiistened by hinges. Wlien this has 

 been lowered until no more space is left tium just 

 suffices lor the opening of the shutter, the latter is 

 permitted to open, and the cement t;\lls to the bot- 

 tom. A second case full is lowered and deposite 

 beside this, and the surface of the two masses 

 levelled by rakes and other appropriate instru- 

 ments. Wiien a unilbrm bed, of about a loot in 

 thickness over the bottom of the whole space in- 

 closed by the wooden partition has been thus de- 

 posited and spread, blocks of stone of not more 

 than eight inches cube are thrown upon the ce- 

 ment, until an entire layer of such stones has been 

 spread over the cement, in which they are capa- 

 ble of partially embedding themselves by their 

 own weight. Upon these a second layer of ce- 

 ment is spread by means of the case, which is fol- 

 lowed by a second layer of stones, and thus the 

 level of the surlace of the water is reached. The 

 case however becomes useless when the depth of 

 water is less than twice tlie vertical dimensions of 

 the case. Alter the structure has been raised thus 

 high, the cement is thrown in by baskets and 

 hods, and the last courses may even be laid by the 

 trowel. 



In Europe, the wood which encloses this struc- 

 ture is usually removed, and may be employed 

 again for the same purpose, but when wood is 

 abundant it would probably be belter to leave it 

 as a protection to the structure, until it decays, 

 when the masonry will probably be perfectly con- 

 solidated. 



Terras, both native and artificial, may be used in 

 the same way. So also may the powder of burnt 

 clay or brick, of calcined ochre, and roasted clay 

 slate. 



Terras is prepared from a columnar greenstone 

 or trap rock found near Andernach on the banks 

 of the Rhine. This is roasted and reduced to 

 ])owdcr. A similar stone is found on the bank of 

 the Hudson near Fort Lee, and might no doubt 

 be used for the same purpose. Otlier varieties of 

 trap rock or basalt may be prepared for a similar 

 use, by heatinjx them until they begin to fuse, and 

 grinding them to powder. 



IJijdraiikc Lime. — Hydraulic lime is calcined in 

 tfie same manner as common limestone. It is 

 prepared by grinding it in a mill to a fine powder, 

 and ought to be kept for use in tight casks. Any 

 limestone which contains from 9 to 10 per cent, of 

 argillaceous matter is slighter hydraulic, and it 

 possesses tfiis projjerty in perfection wdien the pro^ 

 portion of that compound amounts to 20 or 30 per 

 cent. 



An artificial cement may be prepared by mix- 

 ing 3 parts of chalk with one of clay, tempering 

 the mixture with water, forming it into bricks, cal- 

 cining, and grinding to powder. Care must be 

 taken, that, while the heat must be sulIIcieiUly in- 



tense not only to drive oU' the carbonic acid from 

 the chalk, but also the last portion of water from 

 the clay, the mixture does not begin to fuse, for, 

 after this stage is reached, the hydrate can no 

 longer be formed. 



It was long supposed that the hydraulic limes 

 and artificial cement could not be used in building 

 in a mass of water, by tlirowing in loose stones 

 upon a bed of cement mixed with cjiip stone, as 

 described under tiie head of Puzzolana. But re- 

 cent exp^eriments in France liave sliown that tliis 

 idea is untbunded, and that tlie hydraulic limes 

 mixed with common sand, have all tlie properties 

 of the cements of which Puzzolana or Terras 

 form a portion. It is necessary however, to ex- 

 amine experimentally the length of time which 

 they take to set beneath the surlace of the water, 

 for this will differ with the different varieties of the 

 natural mineral ; and where the rate of setting is 

 not such as to render the mixture hard within a 

 lew hours, the mixed cement and chip stone must 

 be allowed to lie in lieaps until it becomes hard at 

 the surlac % before it is plunged into the water. 



Homan Cemml. — This celebrated article is pre- 

 pared in England from a stone found in nodules 

 in the geological formation called the London 

 clay. It is a compact substance of a brown color, 

 susceptible of high polish, it is usually divided 

 into irregular masses by vains of crystilized carbo- 

 nate of lime. The quantity of silica and alumina 

 contained in the brown portion is sufficient to form 

 the cement without any further addition, when 

 it Is to be used beneath the surface of water. 

 When thus unniixed it will .set, either in the open 

 air or in contact Avith water, in not more than fif- 

 teen minutes. Its properties in the two cases are 

 however different, lor it does not, if used unmixed, 

 increase in hardness aiier it has once set, when 

 merely exposed to the air; but if immersed in 

 water, or in damp position, it: gradually acquires 

 the firmness of tlie strongest native limestone. It 

 should therefore never be employed pure, except 

 when it is to be exposed to the action of water. 

 Where it is used merely in a moist place, two 

 parts of good sharp sand should be tnixed with 

 three of cement ; if in a position exposed to frost, 

 three parts of sand to two of cement ; while in a 

 dry and warm climate or in covering walls exposed 

 to the sun, at least five parts of sand should be 

 mixed with two of cement. It is probably owing 

 to the Roman cement, when applied as a stucco, 

 having been used pure, and laid upon dry brick, 

 that its use has been attended with little success in 

 this country, tor when properly prepared and aj)- 

 plied, it has borne e(|ually well the extreme cli- 

 mate of (yanada, and the torrid air of the West 

 Indies. Its use also requires an experienced work- 

 man. When if is to be mixed with sand, the two 

 materials must be tlioroughly incorporated before 

 water is added. 



A stone, identical to that which the Roman ce- 

 ment is prepared, has been found at Boulogne, in 

 France, and one similar in texture, and in being 

 veined with carbonate of lime, at Cumberland in 

 Maryland. The poor calcareous ores of iron, 

 found in coal formations, have also been used in 

 preparing a cement, which has all the properties 

 of the iloman. and goes by the same name. The 

 material wlience Roman cement is prepared Jias^ 

 also been used in England in the preparation of 

 artificial stone. For this purpose the cement 



