STONE, PKESERVATION OP 919 



&c., as the material produced is very regular, and nothing escapes tho jaws of this 

 particular machine larger than |-inch cube, of which size it is capable of producing 

 about 25 tons of material per day. The crushing jaws are arranged on each side of 

 the main shaft, and at every revolution two strokes are given, which renders it double 

 acting ; and, if found necessary or requisite, one pair of jaws may be set to such a 

 gauge as to produce larger material than the others, or both may be set either to a fine or 



1915 



coarse gauge (fig. 1915). In practice it is found necessary to reduce large pieces to about 

 2-inch cubes in one side of the machine. They are then placed in the other and reduced 

 to fine material, and by this means a very large amount of work is done with very little 

 power. The action of this machine will be readily understood without a drawing. 

 All the bearings are protected from dust, and the apparatus is so simple that every 

 part may be got at with ease. The machine does not weigh more than 30 cwts., and 

 for mining enterprise, colonial or otherwise, this is of importance. There is no over- 

 flow, and all pieces of stone put into the hoppers are reduced in equal proportions. 

 There are only three bearings in the whole apparatus. The crushing surfaces do not 

 weigh more than 1 cwt. each, and are easily replaced. 



A powerful stone-crushing machine has also been introduced by Mr. Goodman. 



STONE, PRESERVATION OP. The attention of the scientific world has for 

 some time past been directed to the importance of providing a means for protecting 

 the stone of our public buildings from the ravages of time and the injurious effects 

 of the polluted atmosphere of our manufacturing and populous districts. 



The principal cause of the ruinous decay which is so apparent in the national 

 edifices, churches, mansions, &c., of this country, is generally admitted to be the 

 absorption of water charged with carbonic or other acid gases, which by its chemical 

 action either decomposes the lime or argillaceous matter forming the combining 

 medium uniting the several siliceous or other particles of which the stone is composed, 

 or mechanically disintegrates those particles by the alternate expansion and contrac- 

 tion caused by variations of temperature. 



Many processes have from time to time been suggested, and several patents secured, 

 for filling up the pores of the stone, and thus preventing the admission of these dele- 

 terious agents, but they have been mostly if not entirely composed of oleaginous or 

 gummy substances or compounds, which, although possessing for a time certain pre- 

 servative properties, become decomposed themselves upon exposure, and constantly 

 require to be renewed ; whilst from the nature of these applications the discoloration 

 necessarily produced is highly objectionable. 



The process of silicatisation introduced by Kuhlmann has the disadvantage of 

 requiring some considerable time before tho atmosphere can do its work of effecting 

 the necessary combination between the silica applied in solution to the stone, and tho 

 lime contained in it, and therefore when it is applied to the external parts of any 

 building it is liable to be washed out before solidification has been secured. Mr. 

 Frederick Eansome, advancing from his siliceous-stone process a step farther, meets 

 the condition by effecting a chemical change at once within the stone. Mr. Rausome 

 thus describes his process : 



The mode of operation is simply this : The stone or other material, of which a 

 building may bo composed, should be first cleaned by the removal of any extrane- 

 ous matter on the surface, and then brushed over with a solution of silicate of 

 soda or potash (the specific gravity of which may bo raised to suit the nature of 

 the stone or other material) ; this should be followed by a solution of chloride of 

 calcium, applied also with a brush; the lime immediately combines with tho silica, 

 forming silicate of lime in the pores of the stone ; whilst the chloride combines with 

 the soda, forming chloride of sodium, or common salt, which is removed at once by 



