224 Application of Dialysis to the Preservation of Building Stones. 



APPLICATION OP DIALYSIS TO THE PEESEEVA- 

 TION OP BUILDING STONES. 



The discoveries of Mr. Graham regarding the process of dialysis 

 were described in a paper by Mr. Tegetmeier in our last volume. 

 The prognostic of the speedy application of the process to the 

 useful arts has been rapidly verified in a practical application 

 of very considerable interest. 



The ease with which, by the aid of dialysis, solution of 

 silica (flint) of almost any strength can now be prepared, has 

 suggested its use as a cementing material for binding together 

 the particles of porous and perishable stones, and other similar 

 materials. This application was originally proposed by Mr. 

 W. Crookes, but it has been found that there are some draw- 

 backs to its employment. The flint solution, in many cases, 

 gelatinizes on the surface of the stone, and, drying up, scales 

 off, bringing with it the outer particles of the stone surface. 

 Mr. A. H. Church, whose researches on the formation of certain 

 silicious minerals we have already noticed in the Intellectual 

 Observer, has improved this process so as to obviate its defects. 

 He attains this result by the use of a solution of baryta in the 

 first place, the flint solution being applied afterwards ; in some 

 cases where the nature of the materials to be operated upon 

 requires it, the order of application of these solutions is reversed. 

 The effect of the completed process is very marked. Porous 

 stones become almost non-absorbent ; their hardness is greatly 

 increased, and their liability to injury from atmospheric in- 

 fluences, almost, if not entirely, removed; brick, terra-cotta, 

 and many other materials are likewise rendered nearly water- 

 proof, while plaster of Paris casts are greatly improved in 

 durability and appearance by this treatment. 



The rationale of the process is very simple. The successive 

 application of solutions of baryta and of silica causes the de- 

 position within the substance of the stone of the insoluble and 

 unalterable silicate of baryta ; no soluble, and therefore un- 

 necessary and injurious, salt being produced, as is the case in 

 other processes for the preservation of stone from decay. 

 Where, for instance, silicate of soda and chloride of barium are 

 successively applied, not only is silicate of baryta formed, but 

 also an equivalent proportion of chloride of sodium or common 

 salt. By the washing out of this soluble compound by the 

 action of rain, the continuity of the protective coating is im- 

 paired; and if the salt be not removed more serious con- 

 sequences may ensue by its crystallization, deliquescence, or 

 efflorescence. 



