CEMENTS. 



565 



iron-work in the open air — namely, \ oz. 

 of aquafortis, 1 gallon of gas-tar, and \ 

 -pint of spirits of turpentine, gradually and 

 well mixed together in an iron vessel, and 

 over a slow fire. The colour of the gas- 

 tar predominating, renders this paint more 

 fit for field fences than for garden build- 

 ings. 



§ 9. — CEMENTS. 



The most useful cement, and conse- 

 quently the one in general use, is the 

 Roman cement, of which there are two 

 kinds — Parker's, and Atkinson's or Mid- 

 grave's, which is the same thing. Parker's 

 is the oldest, and is said to have been 

 accidentally discovered by a person of 

 that name. Parker's cement is made of 

 the nodules of indurated and slightly 

 ferruginous marl, called by mineralogists 

 septaria, and also of some other kinds of 

 argillaceous limestone. These are burnt in 

 conical kilns, in a similar manner to 

 other limestone ; great care is, however, 

 taken not to use too much fire, as, if the 

 slightest degree of fusion takes place, it 

 will be rendered useless. When properly 

 roasted, it is then ground to fine powder, 

 and packed in air-tight barrels, and kept 

 quite dry. 



Atkinson's or Mulgrave's is next in pri- 

 ority, and has long been manufactured on 

 the Mulgrave estate near Whitby. It 

 became known as Atkinson's cement in 

 consequence of that eminent architect, the 

 personal friend of the late Lord Mulgrave, 

 introducing it into more general use. He 

 also superintended the sale of it in Lon- 

 don for many years, and had a depot near 

 Blackfriars' Bridge — " Atkinsons Cement 

 Wharf." At Lord Mulgrave's death he 

 gave up all connection with it, and since 

 that time it has been generally known as 

 Mulgrave's cement. There is a consider- 

 able difference in the quality of these two 

 varieties, Mulgrave's being' of a lighter 

 colour and more ochrey than Parker's, 

 much higher in price, and proportionably 

 superior in strength and durability. Both, 

 however, are easily destroyed by being 

 kept in damp places and exposed to the 

 air, in which cases neither are much better 

 than good lime ; and hence the disrepute 

 they often fall into from improper keep- 

 ing. Mulgrave's is manufactured in the 



same way as Parker's cement, noticed 

 above. 



Bailey's cement. — This is a hard and 

 durable material, and is formed of stone- 

 lime recently burnt, and, immediately 

 after being slacked, mixed with clean 

 sharp sand. The usual proportions are 

 three of sand to one of lime. 



Frosfs cement is better calculated to in- 

 durate with lime than Roman cement, 

 because it does not set so fast. The in- 

 ventor has stated in " The Repertory of 

 Arts " that lime, even chalk lime, burned 

 in a close kiln, and cooled without coming 

 in the slightest degree in contact with the 

 atmosphere, will, when afterwards slacked 

 and mixed with sharp sand, set as rapidly 

 as Roman cement, and this even under 

 water. 



Frosfs cement is made by grinding 

 chalk very finely in a mill, water being 

 mixed with it during the process, which 

 carries off its lightest particles to a reser- 

 voir. The same machinery is employed 

 at the same time grinding clay, which is 

 also washed with water, and the lighter 

 particles also conveyed to the same reser- 

 voir. This combination of chalk and 

 thirty per cent of clay is evaporated till 

 quite dry, then burnt in a kiln and ground 

 to powder, when it is fit for packing by 

 in air-tight casks to keep, or for imme- 

 diate use. It is much cheaper than Ro- 

 man cement, and requires no sand to set it. 



Puzzolano earth cement, and tarras ce- 

 ment, like Frost's, indurate freely w 7 ith 

 lime, and do not set so quickly as Roman 

 cement does. 



Gypsum, like Roman cement, sets al- 

 most instantaneously, whether mixed with 

 sand or not. 



Mastic is a calcareous cement, consist- 

 ing of earth and other substances almost 

 insoluble in water, to which, when pul- 

 verised, are added any of the oxides of 

 lead, and also a quantity of glass or 

 pounded flints ; the whole, when finely 

 pounded, is mixed with any cheap vege- 

 table oil. This cement, when made, may 

 be kept in casks for years without injury, 

 and is of all others the best for producing 

 an imitation of stone, but it is much too 

 expensive to be brought into general use. 



Metallic cement is formed of scoriae 

 from the copper-works and stone-lime, 

 both finely pounded. It sets rapidly, and 

 takes a fine polish. 



