•STIJCCO FOR PRESERVING STONE. J5 



their acid, to give it a sort of covering, that would render it 

 as unalterable as the stone of Logozan in Estrainadura, It 

 is equally known, that sulphate of barytes resists all agents 

 in the humid way; and we might certainly coat the stone 

 with this earthy salt, by first impregnating it with a solutioa 

 of sulphate of iron, zinc, magnesia, alumine, &c., and im- 

 mediately washing it over with barytes water *. The inso- 

 lubility of oxalates and tartrates of lime, and the adhesioa 

 they contract by deposition even on polished substances, 

 suggest processes for washes not less solid ; as the acids added 

 to these salts to render them temporarily soluble, saturating 

 themselves with their base from the substance of the stone 

 itself, would not fail to connect together all the grains, fill 

 up their intervals, and completely close the pores. Trials 

 made with a view to ascertain the justice of this reasoninjr 

 have conBrmed the expectation of a successful result; since 

 on the most porous stones they have produced a surface, oa 

 which the eye could see no appearance of coating, but which, 

 being rubbed with wet black cloth till the cloth showed signs 

 of wear, was not in the least soiled by it. 



Preparations of this kind however would be much more The lat»er to» 

 expensive than Bachelier's stucco, so that their use must be expensive, 

 restricted to the preservation of sculpture of extreme deli- 

 cacy. 



For farther satisTaction trials have been made with diffe- General re- 

 rent kinds, of stone, and stucco made in imitation of Bache- ^"^** ^ **P'^ 

 Uer's. These have given rise to the following observations. 



1. All the compositions in which alum water was employ- 

 ed soiled the fingers, and were washed off by water. 



2. The cheese that acquires the greatest consistency with 

 dry substances is that which is almost entirely deprived of 

 the butyraceouj* and wheyey parts. Mr. d'Arcet, in the 

 paper already quoted, had remarked, that these were more 

 detrimental than useful, that painting with milk would not 

 resint water, and that the cheese called/roDifl^e d la pie might 



♦ Accident furnlihed Mr. d'Arcet with a striking proaf of the readi- Fikering stone 

 ness with which this change Of bases by superior affinity will fill the pores spoiled by *c- 

 •f the most porous stones. A capsule full pf stiontian water happening cideat. 

 to be overturned inie a filtering 8t«ne, it never after let throwf b a sis jie 

 dr»p of water, 



be 



