BUILDING MATERIALS. 



203 



or the more permanent gums and resins. Fi- 

 nally, they think that only the test of some 

 years of experiment and actual use can decide 

 the questions of the actual or comparative 

 merits of these various processes. In these 

 views the general committee coincide; and 

 they accordingly recommend no general coat- 

 ing, painting, oiling, or washing of the build- 

 ing, but only precautions though by what 

 means they scarcely make clear to arrest de- 

 cay where it actually commences, or in the 

 worst cases the cutting out of the decaying 

 stone, until more definite knowledge shall sup- 

 ply a remedy on which full reliance can be 

 placed. 



"IV. The qualities of the stones to be rec- 

 ommended for future use in public buildings in 

 London." This head may here be briefly dis- 

 posed of; since, the London atmosphere being 

 among the most destructive to which building 

 materials can be exposed, and the air of most 

 cities in this country being much more dry and 

 less corroding, the interest in this part of the 

 subject must be for American architects main- 

 ly that of comparison. . The committee con- 

 demn the magnesian limestones as an unsafe 

 material for public buildings in London. The 

 Portland stone, not so hard as the Anston, and 

 yet with a power of withstanding the London 

 atmosphere shown in many buildings from the 

 date of St. Paul's downward, they fully rec- 

 ommend ; though even with this, a careful se- 

 lection at the quarries is necessary. The car- 

 bonates of lime used for buildings in the com- 

 paratively pure atmosphere of Paris, and where 

 wood is largely used as fuel, also suffer decay, 

 which, thus far, the French architects and 

 chemists appear to have been no more success- 

 ful than others in preventing or arresting. The 

 committee close by recommending a persever- 

 ing trial of the various probably valuable pre- 

 servative materials and agents, expressing a be- 

 lief that a large portion of the stone of the new 

 palace is very durable, and that a remedy suf- 

 ficing to arrest or control the decay in the af- 

 fected portion will soon be found. The full 

 report may be consulted in the " London Build- 

 er,'' Xo. 97-4 ; and " Journal of the Franklin In- 

 stitute," Phila., Jan. 1862. 



In a paper read before the Architectural As- 

 sociation (London "Mechanics' Magazine," Feb- 

 ruary, 1862), Mr. A. H. Church laid down cer- 

 tain principles as likely to be practically effec- 

 tive in accomplishing the preservation of stone, 

 among them the following: 1, Any process, to 

 be practically useful, must be easy of applica- 

 tion, and moderate in cost ; 2, It must render 

 absorbent stone less porous, and counteract 

 also the influence of injurious bodies in the 

 air ; 3, It must consolidate stones, the particles 

 of which are loosely aggregated, and harden 

 such as are easily abraded by mechanical 

 means; 4, It must not materially change the 

 color, surface, or texture of the stone ; 5, The 

 protecting material must not remain as a film, 

 but must penetrate the material ; not, however, 



contracting the surface, or otherwise separat- 

 ing particles from the stone ; 6, The material 

 must be less soluble in water and less subject 

 to atmospheric agents than the material of the 

 stone ; 7, Its application must leave no soluble, 

 and especially no efflorescent or crystallizing 

 salt, as one of its products, in the surface or 

 substance of the stone. As a result of some of 

 the so called preservative processes, a sulphate 

 of soda or of magnesia is formed in the super- 

 ficial parts of the stone, which effloresces upon 

 the surface ; and it is curious to note upon the 

 summit of each hair-like crystal a minute frag- 

 ment of stone, torn off and carried forward by 

 the force of the crystallization. Again, when 

 a strong aqueous solution of silica is applied to 

 chalk or a soft limestone, the silica glutinizes 

 on the surface ; the film formed scales off, and 

 the scales bring away with them adherent par- 

 ticles of the chalk or stone upon their inner sur- 

 face. The principles and remarks here offered 

 have doubtless a reference to Mr. Church's pro- 

 cess of preservation, presently to be named. 



At a stated meeting of the members of the 

 Franklin Institute, Philadelphia, December 19, 

 1861, Mr. A. L. Fleury read a paper on the sub- 

 ject of preserving building stone by applying a 

 pure aqueous solution of silica, adding other 

 uses of the same solution. He first referred to 

 the very elaborate and quite exhaustive paper 

 by Mr." J. M. Ordway, on "Water Glass" 

 ("American Journal of Science," Sept. and Nov. 

 1861, and Jan. 1862), or the various forms of 

 soluble alkaline silicates, originally investigated 

 by Fuchs, Kuhlmann, Liebig, and others. For 

 these alkaline silicates he would substitute the 

 aqueous solution just mentioned ; a sugges- 

 tion made also in the same year by Mr. W. 

 Crookes, editor of the " Chemical Xews.'' Mr. 

 Fleury proceeds to quote from the last named 

 journal, Xo. 100, giving several modes of pre- 

 paring the soluble silica. The difficulty which 

 besets many of the processes of silicification is, 

 that along with the needful silica, so much 

 superfluous, and indeed injurious matter is 

 often introduced, that the valuable qualities of 

 the silica are in a great measure counteracted. 

 Of the four modes given for preparing the pure 

 solution, which at least has the merit of ex- 

 cluding these useless or hurtful intermixtures, 

 we name the two which appear to prove most 

 satisfactory: 1. By dissolving pure sulphide of 

 silicium in water; sulphuretted hydrogen is 

 given off, the silicium is oxidized, and the re- 

 sulting silica remains completely dissolved, in 

 such proportion, moreover, that the liquid 

 gelatinizes upon attempting to evaporate it. 

 2. By Prof. Graham's new method of Dialysis. 

 (See CHEMISTRY.) In this, a solution of silicate 

 of soda, supersaturated with hydrochloric acid, 

 is placed on one side of a parchment paper 

 septum, pure water being on the other side : in 

 a few days the hydrochloric acid and chloride 

 of sodium will be found to have completely 

 passed through the diaphragm, leaving the 

 silica in aqueous solution, and so pure that acid 



