268 ANNUAL OF SCIENTIFIC DISCOVERY. 



silicate of potash was sufficient to effect a superficial consolidation of the 

 stones, varying with their porosity. 



Upon sulphate of lime or plaster of Paris the action of silicate of potash is 

 essentially the same; but it is more rapid, and has the disadvantage of giving 

 rise to tlie formation of sulphate of potash, which, on crystallizing, disag- 

 gregates the surfaces. Consequently, the silicious solution ought to be more 

 diluted, so as to render the action slower; the consolidation, however, must 

 be sufficient to avoid the effects of the crystallization of sulphate of 

 potash. 



Mode of Application. In what way does Mr. Kiihlmann apply the silicate 

 of potash upon monuments and buildings in general? He takes silicate of 

 potash prepared in his works, and possessing the composition of soluble 

 glass, and dissolves it in twice its own weight of water. This solution is to 

 be had in commerce, and marks 35 of Beaume's areometer. All that is 

 required is to dilute this with twice its volume of water, in order to obtain 

 the degree of concentration most convenient for the process of hardening. 

 In recent buildings it may be applied at once; older constructions require to 

 be cleansed by washing with a hard brush, or by means of a solution of 

 caustic potash, and most frequently by smart scraping. Large surfaces are 

 sprinkled with the silicious solution by means of pumps or large syringes 

 with divided jets. The latter have been employed in Germany since 1847. 

 Care must be taken to collect the excess of liquid by means of gutters of 

 glazed earthenware placed at the foot of the walls. For sculptures and 

 certain portions of buildings, soft brushes are employed, and with great 

 advantage, also the painting-brush. Experience has shown that three 

 applications of silicate, on three consecutive days, suffice to harden stone. 

 The quantity of solution which is absorbed varies with the nature of the 

 stone and its porosity; the cost of silicate does not exceed seventy-five cen- 

 times (fifteen cents) per square metre for the most porous stones. 



Dyeing of Stones. Mr. Kiihlmann, observing that the silicification of 

 buildings and sculptures gave rise to various colorations, which rendered, 

 for instance, the joints more marked, was led to seek a remedy for these 

 colorations. By means of a double silicate of manganese and potash he 

 obtained a dark solution, which could be applied to very white limestones. 

 By suspending some artificial sulphate of baryta in the silicious solution, he 

 was able to introduce a little of this sulphate into the porous stone, together 

 with the silica, in such a manner, as to whiten surfaces of too dark a hue. 

 He proved experimentally that porous limestones, when boiled in solutions 

 of metallic sulphates (the oxides of which are insoluble in water), give rise 

 to the fixation, to a certain depth, of these oxides in intimate combination 

 with the sulphate of lime. With sulphate of iron he obtained a rust-color of 

 more or less intensity; with sulphate of copper, a magnificent green tint; 

 with sulphate of manganese, brown tints; with a mixture of sulphate of iron, 

 and sulphate of copper, a chocolate tint, etc. He observed, at the same 

 time, that the double sulphates thus formed penetrated into the stones, and 

 likewise increased their hardness. 



Silicious Painting. There was but one step from silicification to silicious 

 painting. Fuchs, Professor of Mineralogy at the University of Munich, had 

 already, in 1817, given the famous German painter, Kaulbach, all the advice 

 neee.-'sary to enable him, by means of a sprinkling with silicate of soda, to 

 fix the fresco-paintings which were then executed in the new museum at 

 Berlin. Mr. Kiihlmann went further, and applied the colors directly by 



