Proceedings of the Polytechnw Association: 977 



various causes, and tliat amons; these is a very iniiiute litchcn, tlie 

 Lepra antupiitatis, wliicli is one of the worst enemies of stone; and 

 its action is to such an extent tliat, for instance, the beautiful marble 

 scul[)tnres of the well-known Pare de Versailles will, unless proper 

 measnres be taken fur staying- the process of decay, be nnsightly and 

 uu'Iy masses of dirt, and quite irretrievably lost, as works of art, 

 witiiiu tlie next fifty years. The antlior, taking as instances such 

 buildiiio's at Paris as tlie I>oni-1)on Pahace, the Pakvis du Corps 

 Legiskatif, the Mazarin Palace (I'lnstitut), the Mint, and otliers, 

 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 

 ]>romotes the dei)osition of dirt and dust. Various places and 

 instances are cited of the application of oxyd of copper and its salts, 

 which places are open to inspection, and the lengtli of time which 

 has elapsed since such application, seems to warrant the conclusion 

 that these compounds act as preservatives of stone. In reference to 

 granite, the author states tliat this stone is also, according to the 

 experience of Egyj^tian engineers, far more readily affected by a 

 moist climate than one w^ould be led to believe. The obelisk of 

 Luxor, brought from Ujiper Egypt to Paris, has become blanched and 

 full of small cracks, during the forty years it has stood on the Place 

 de la Concorde, although forty centuries had not perceptibly affected 

 it as long as it was in Egypt. Granite, in a moist climate, becomes 

 the seat of minute crj^ptogamic plants, which greatly aids its destruc- 

 tion ; and it is, moreover, a well-known fact, that the disintegration 

 of this stone, which is composed of three separate minerals (quartz, 

 mica and feldspar), depends very greatly upon the thorough and 

 intimate mixture, as well as the chemical composition of these three 

 ingredients, each of which, in a separate state, more easily withstands 

 tlie influence of the weather. 



Is THE Potato DisexVse IIereditaky. 



A correspondent of an English journal of liorticulture says he 

 planted in 1805 some pink kidney potatoes of a late keeping kind, 

 called Yorkshire kidneys. They ])roduced niucli liaum, and are a 

 little given to disease. Tlie crop was diseased. He selected from the 

 diseased potatoes twelve of the very worst, so bad, so rotten, as 

 scarcely to have any vitality, and planted tliem, in March, 1866, 

 on a }iiece of pour ground without any manure. The result was 



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