K. MECHANICS AND ENGINEERING. 401 



mixture are to be applied successively, while hot, but only in 

 dry, warm weather. 5 (7, Tin., 64. 



PEEVENTION OF MOISTUEE IX TUNNELS. 



By a system of tubes and pipes laid between the masonry 

 of a subterranean tunnel and the mountain wall, and connect- 

 ing with other drain-tubes leading to the exterior, an Austrian 

 engineer has succeeded in rendering the tunnel completely 

 dry. 6 C, August 11,322. 



COMBUSTION OF COAL-DUST. 



An enormous amount of coal in the form of dust and small 

 fragments is every year wasted in our coal mines, and, al- 

 though many propositions have been made to utilize it by 

 consolidating it into bricks, it has been found that the expense 

 of this is greater than that attendant upon the extraction of 

 large coal, and consequently the waste has still continued. 

 It has been ascertained, however, that by taking fine coal-dust 

 and placing it in a furnace, with the exact quantity of air 

 which is requisite to effect the combustion of the coal, a mass 

 of flame is obtained of the highest temperature, which does 

 its work effectually, and emits no smoke whatever from the 

 chimney. The results promised from this method of using 

 fuel are so striking as almost to render it probable that, when 

 dust can not be obtained, the coal itself will be reduced to 

 powder for the purpose before being placed in the furnace. 

 15 A, Jem. 28,117. 



CONCEETE FOE BUILDING PUEPOSES. 



Such of our readers as are unacquainted with the value and 

 importance of a new concrete, invented by a French engineer 

 M. Coignet and bearing his name, will probably be sur- 

 prised to learn that, at a comparatively small cost, works of 

 the greatest magnitude are now made, as well as those pos- 

 sessing the utmost durability. An elaborate report on this 

 subject has lately been printed by the State Department 

 among its series of reports on the Paris Exposition of 1867, 

 and, if no other service had been rendered in return for the 

 expenditures made by the United States in connection with 

 the Exj)Osition, this one work alone would be more than an 

 equivalent in bringing to our notice so important a material. 



