L. MECHANICS AND ENGINEERING. 465 



made of it. It is said to resist fire and the atmosphere, and 

 also to be well adapted to water-walls. 8 C, Dec. 17, 1874, 

 449. 



PRESERVATION OF CLAY PAVING-BRICKS. 



According to experiments made in Stuttgart, it was found 

 that bricks that had been coated three times with linseed- 

 oii were less smeary, from wear, in wet weather, as well as 

 more free from dust in summer, than those that had not 

 been so treated. The cheaper petroleum residues were also 

 employed instead of the linseed-oil. Saturation of paving- 

 bricks, sandstone, etc., about manufactories, with hot tar, is 

 also highly recommended where the black color is not objec- 

 tionable. 5 C, XXXIL, 255. 



INCREASING THE ADHESIVE POWER OF CEMENT. 



According to Walters, the force of cohesion in cement may 

 be increased in three ways : by pressure from without ; by 

 increase in the volume of single constituents; and by dis- 

 placement of single constituents, produced by their solubil- 

 ity, taken in connection with attraction and crystallization. 



The first of these actions may be greatly facilitated by the 

 workman with his trowel ; the absorption of water and car- 

 bonic acid from the air produces an increase of volume ; and 

 the solubility of some constituents effects their transporta- 

 tion to places where the pressure is comparatively small, 

 and where, on subsequent solidification, they serve to bind 

 the whole more firmly together. The second of these proc- 

 esses is the most important, but unless the proportion be- 

 tween the space left for expansion and the expansion itself 

 be regarded, the mortar will not hold. 



According to the author, the chief desideratum of a good 

 mortar is that it shall become impervious to moisture on the 

 outside. This is best fulfilled by Portland cement, which, in in- 

 creasing in volume, becomes almost entirely indifferent to the 

 action of carbonic acid and moisture. 21 A, July^ 1874, 671. 



PRESERVATION OF TIMBER. 



Several notices have recently appeared in regard to the 

 merits of the patent process of Rev. Dr. Jones, of Tavistock, 

 England, for rendering timber uninflammable, and prevent- 



F2 



