MECHANICS AND USEFUL ARTS. 103 



also offers a prize to those who intrcduc? a new branch of industry into 

 the department of the Haut- Rhino. This last prize was taken by MM. 

 Moerhlin and Stoll, who manufacture sal-ammoniac from the ammoniacal 

 liquid of gas works. The main difficulty in the operation consists in sep- 

 arating the tar-like material which it contains. The following is the 

 process adopted : 



The ammoniacal liquid is mixed with slaked lime ; then submitted to 

 distillation in a boiler heated by steam ; the parts volatilized pass into a 

 worm, in which the larger part of the tar is deposited ; the ammonia 

 passes on into a Wolff's apparatus, where it leaves the foreign substances 

 present, and finally is carried into cold water, where it is condensed. In 

 this state it is nearly free from its impurities ; it is neutralized with chlo- 

 rohydric acid, and evaporated in a lead boiler. As it deposits, it is with- 

 drawn by means of a wooden rake ; it is allowed to drain, and then 

 introduced into a brick mould, and subjected to strong pressure. Blocks 

 of sal-ammoniac are thus obtained, which are dried in an oven heated by 

 part of the heat furnished by the evaporating furnace. 



IMPROVEMENTS IN PAVING. 



Messrs. Parker & Co., Engineers, England, have recently introduced a 

 novel system of construction for the pavement of roads, bridges, &c. Pro- 

 ceeding 011 the principle that the inequalities in the best of pavements are 

 first caused by the partial collapse or sinking of the foundation, or sub- 

 strata, they have to a certain extent rendered the finished portion of 

 the road independent of the homogeneity and solidity of the concrete 

 beneath. The plan consists in easting in sections of three feet square a 

 series of iron boxes, beds, or chambers, eight inches long, three broad, 

 and four deep, into each of which a block of wood is placed, with the 

 grain in a vertical position, or a block of granite, made to fit with moderate 

 exactness, and standing about two inches above the iron framework. By 

 this arrangement the total rmrnber of sectors being made to break joint, 

 and firmly keyed together, gives great solidity, avoids all tendency to par- 

 tial sinking in holes, secures a good foot-hold for the horse, whether gravel 

 is used as an upper casting or not ; and as one or more blocks, more soft 

 than others, show signs of wear or decay, they may be instantly and with 

 great facility removed and replaced by others. Another peculiar feature 

 may be noticed, which will prove a source of economy ; it is proposed to 

 make the compartments for streets of the greatest thoroughfare the deepest, 

 and for secondary streets less deep, and for third class more shallow 

 still. By this means, when the blocks are so worn as to require removal 

 in a first-class street, they may be removed to another street. London 

 Mining Journal. 



