PRESERVATION OF TIMBER, &c. 



567 



These, when calcined and reduced to 

 powder, and mixed with fine sharp 

 sand, are fit for use. These three 

 cements harden speedily under water, 

 and are very durable. " The art of 

 mixing earths so as to form mortars which 

 will set or solidify, either by themselves 

 or in conjunction with stones and bricks, 

 can only be scientifically understood 

 through some knowledge of chemistry. 

 All lime mortars depend for their 

 strength on their quality of absorbing 

 carbonic acid gas and water, and solidify- 

 ing them. All cements are rapidly 

 solidifying mortars, though they depend 

 for their strength on the same qualities 

 as lime mortar, owe their power of rapid 

 solidification to the presence of some 

 metallic oxide, the value of which prin- 

 cipally results from its capacity of absorb- 

 ing oxygen." — Villa Architecture. Much 

 of the value of all mortars and cements 

 depends on the purity and quality of the 

 sand used; indeed, for such purposes it 

 should almost invariably be washed, to 

 free it from earthy matter. 



Water cement of Dihl. — Pure clay, dried 

 by a gentle heat, and powdered, mixed 

 up to the consistence of a paste with 

 boiled linseed oil, may be used with 

 advantage for covering the walls of 

 houses, the roofs of verandahs, &c. It 

 may be coloured to fancy by the use of 

 any of the ochres, and may be thinned 

 by turpentine. 



Patent antonica, an invention of Mrs 

 Marshall, and lately brought into notice 

 by her, is a valuable discovery. Of its 

 component parts we are of course igno- 

 rant, as well as of the mode of manufac- 

 turing it. That the first is of cheap 

 materials, and the latter easily accom- 

 plished, may be concluded from the 

 extremely low price at which very beau- 

 tiful articles of it are sold. It can be 

 moulded into any form, however elabo- 

 rate, and made very closely to resemble 

 all kinds of marbles, granites, &c. 



Oropholite cement has been pretty exten- 

 sively used as a substitute for lead, zinc, 

 slates, tiles, &c, for covering roofs, and 

 also for lining cisterns and tanks. When 

 employed for the former purposes, it is 

 spread on thick canvass, and either laid 

 on the rafters in webs, or cut into smaller 

 pieces, and laid on in the form of tiles. 

 It has been recommended as being both 



cheap and durable, — a non-conductor of 

 electricity, resisting oxidation, perfectly 

 waterproof, and preventing damp from 

 passing through walls. When laid on 

 large surfaces, the joining should be 

 covered with the cement of which it is 

 made, so forming the roof entirely in one 

 piece, preventing alike the entrance of 

 water and the displacement of any part 

 of it by the wind. We have seen it 

 employed as a cement laid on walls in 

 the ordinary manner, like plaster, and 

 also for covering the sides and bottoms 

 of tanks, where it appears to stand well ; 

 but we doubt its durability as a roofing 

 material when laid on canvass, as the 

 latter is so liable to decay. To our 

 enumeration of building cements, we 

 may add the following as being much 

 used in Scotland, and manufactured 

 there — viz., Calderwood cement, Borrows- 

 townness cement, Broxburn cement. This 

 latter is of inferior quality. 



Cements are valuable for garden 

 purposes, such as building pits where 

 the walls are necessarily narrow, yet re- 

 quiring strength, building or pointing 

 garden walls, making tanks and cisterns, 

 and various purposes in connection with 

 the imitations employed in ornamental 

 gardening. 



§ 10. — ON THE PRESERVATION OF TIM- 

 BER USED IN HOTHOUSE-BUILDING, 

 AND ON THE DURABILITY OF MATE- 

 RIALS. 



Unseasoned timber, and that of trees 

 cut before they have arrived at full 

 maturity, are equally liable to premature 

 decay. The alburnum or immaturely 

 formed portion of the wood undergoes, 

 in consequence of the moisture or sap 

 contained in it, a process of fermenta- 

 tion, which affords food highly relished 

 by a certain class of microscopic insects, 

 whose keen perception leads them to find 

 out its presence. These insects perforate 

 the wood in all directions, and in so 

 doing make innumerable cavities, into 

 which the air and moisture enter. A 

 combination takes place with these and 

 the nitrogen existing in the fermenting 

 alburnum, producing ammonia and its 

 compounds, highly favourable to the 

 growth of the various species of minute 



