68 ANNUAL OF SCIENTIFIC DISCOVERY. 



placed in such a position to drip that the thickness of the varnish 

 shall be uniform. 



The coating on the pipes and castings must be tenacious when 

 cold, and not brittle, nor disposed to scale off; and when it shall 

 appear to the inspector that the coating has not been satisfactorily 

 applied, the pipe or casting shall be thoroughly scraped, cleaned, 

 and recoated. 



COATING FOR OUTSIDE WALLS. 



The following coating for rough brick walls is used by the 

 U. S. Government for painting light-houses, and it effectually 

 prevents moisture from striking through : Take of fresh Rosendale 

 cvnient 3 parts, and of clean, fine sand 1 part; mix with fresh 

 water thoroughly. This gives a gray or granite color, dark or 

 light, according to the color of the cement. If brick color is de- 

 sired, add enough Venetian red to the mixture to produce the 

 color. If a very light color is desired, lime may be used with the 

 cement and sand. Care must be taken to have all the ingredients 

 well mixed together. In applying the wash, the wall must be wet 

 with clean fresh water ; then follow immediately with the cement 

 wash. This prevents the bricks from absorbing the water from 

 the wash too rapidly, and gives time for the cement to set. The 

 wash must be well stirred during the application. The mixture 

 is to be made as thick as can be applied conveniently with a 

 whitewash-brush. It is admirably suited for brick-work, fences, 

 etc., but it cannot be used to advantage over paint or whitewash. 



PRESERVATION OF STONES. 



Dr. Robert, in the Paris " Les Mondes," maintains that the use 

 of the black oxide of copper, and its salts, will effectually prevent 

 change in stone. He shows that the decay of granite, marble, 

 limestones, sandstones, and all natural building stones, is the 

 combined effect of various causes, and that among these is a very 

 minute lichen, the Lepra antiquitatis, which is one of the worst 

 enemies of stone, and its action is to such an extent that, for in- 

 stance, the beautiful marble sculptures of the well-known Pare 

 de Versailles will, unless proper measures be taken for staying 

 the process of decay, be unsightly and ugly masses of dirt, and 

 quite irretrievably lost, as works of art, within the next 50 years. 

 The author, taking as instances such buildings at Paris as the 

 Bourbon Palace, the Palais du Corps Legislatif, the Mazarin Pal- 

 ace (V Institut} , the Mint, and others, points out that dust, spiders' 

 webs, and the action of rain, combined with the minute lichen 

 above alluded to, hasten the decay of stone, especially of those 

 parts where any sculpture or ornamental carving promotes the 

 deposition of dirt and dust. Various places and instances are 

 cited of the application of oxide of copper and its salts, which 

 places are open to inspection, and the length of time which has 

 elapsed since such application seems to warrant the conclusion 

 that these compounds act as preservatives of stone. In reference 



