L. MECHANICS AND ENGINEERING. 521 



placed in a suitable impregnating vessel, filled with thick, 

 heated coal-tar, under pressure, until thoroughly saturated, 

 and are placed upon and strewed with screened sand, coal- 

 ashes, or the like, and dried. When perfectly dry, they are 

 examined to see whether they are coated thickly enough, 

 and every crack filled with the tar ; if not, this is remedied 

 by brushing with hot tar. The impregnating composition 

 should be similar to that employed in the manufiicture of 

 roofing-paper namely, condensed coal-tar, with the addition 

 of natural asphaltum and some sulphur, the latter imparting 

 a tendency to harden more raj^idly. The spikes, when driv- 

 en, should be dipped in hot coal-tar, and any split opened 

 should be well coated with it. 14 C\ CCYIL, 514. 



UTILIZATIOX OF FUENACE-SLAG. 



Improvements continue to be made in the methods of util- 

 izing furnace-slag, and in converting what was formerly a 

 nuisance into a valuable article of commerce, and one profit- 

 able to its manufacturer. At the Tees Iron-works, in Great 

 Britain, the slag, as it leaves the furnace, spreads itself over 

 a revolving table, and water being poured over it, it is then 

 pushed into the wagons beneath. When cold, it readily 

 breaks into pieces, and forms a useful material for making 

 concrete buildinojs. At the Tees Works some YOOO or 8000 

 tons have been made in a few months past, all of which has 

 been employed in building and drainage works, and it has 

 also been used as a top-dressing for roads over which there 

 is a heavy trafiic. By a special process the slag is converted 

 into sand, from which bricks and cement of an excellent qual- 

 ity are made. 18 A, May 9, 1873, 191. 



COMPAKISOX OF ANCIENT MOETAKS. 



Dr. Wallace, of Glasgow, has been paying some attention 

 to the character of the mortars used in ancient buildings, 

 and, among others, refers to specimens from the Great Pyra- 

 mid, from the Island of Cyprus, from the ruins of Athens, and 

 also from ancient ruins in Rome, and elsewhere in Italy. In 

 a recent communication to the Philosophical Society of Glas- 

 gow, he mentions the remarkable differences between them. 

 In some edifices, as at Baalbec, and some ruined cities in Tur- 

 key, buildings are met with constructed of immense blocks 



