408 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



eral witherite or natural carbonate of baryta. 5 C, xlvii., 

 1870,380. 



RENDERING WALLS WATER-TIGHT. 



It is proposed by Mr. F. Ransome, of London, to render 

 stone and brick walls water-proof by coating them to satura- 

 tion with a solution of silicate of soda, which is superficially 

 decomposed by the further application of chloride of calcium. 

 The surface thus obtained consists of silicate of lime, which 

 is perfectly insoluble, while it does not alter the appearance 

 of the wail. 10 6 r ,rv., 1871, 28. 



ASPHALT FOR PAYING. 



The subject of the best material for paving streets is, of 

 course, one of great importance to all the larger towns and 

 cities, and the favorite at this time in London seems to be as- 

 phalt. The London Mechanics' Magazine is inclined to be- 

 lieve that experiments now being made in London will have 

 a satisfactory result, although it thinks that a heavy bed of 

 concrete, of at least six inches or more in thickness, should 

 be first laid in the more frequented streets of the city. Over 

 this a thickness of two or three inches of asphalt is thought 

 to be sufficient. For small towns both the layer of asphalt 

 and of subjacent concrete may be considerably less in thick- 

 ness perhaps not more than half of that suggested. 3 A, 

 March 24, 205. 



UTILIZATION OP IRON SLAG. 



The utilization of the slag of iron furnaces, which is pro- 

 duced in such immense quantity, has long been a problem, 

 although of late years many attempts have been made to 

 solve it. Methods have been suggested for extracting vari- 

 ous substances of value in the arts ; and in some countries, 

 Belgium especially, the material is cast into moulds of a defi- 

 nite shape, and used, without farther preparation, for build- 

 ing purposes. All persons familiar with the iron districts 

 where this substance is produced are aware of the excellent 

 Macadamized roads it makes in the neighborhood of the iron 

 furnaces; and it is now transported to considerable distances 

 in England for a similar purpose. The best method of ap- 

 plying it is said to be by breaking it up into cubes of about 



