ITALY. LETTER XVII. 24^ 



of travertine, a proof of neighbouring limeftone. 

 Likely they fetch this travertino from Rapolana.-. 



Behind 



Vegnl, in a Letter to ProfefTor Gaetano Monti at Bologna j 

 printed at Bologna, 1761, 410. Dodtor Vtgni has efta- 

 blifhed there a manufaftory, to precipitate this fine tufo on 

 medals and bas-reliefs, and to get by that means the fineft 

 impreffions. He caufes this hot incruftating water to fall 

 from on high into a large vefTel, and to break upon a wooden 

 crofs ; whereby it is feparated into drops, and diredled again ft 

 the fides of the veffel, on which all around, the medals or 

 bas-reliefs, or their mouldings or forms, are hanging. The 

 falling and breaking of the water imparts a greater impulsion 

 to its drops, and to its tufo or tartaro; which, without this 

 manipulation, would be but farinaceous, friable, and fpungy. 

 The above-mentioned agaricus mineralis, in Montagna di S. 

 Fiore, feems to be the very calcareous earth, and fubftance of 

 this fine tufo. The hills about the Bagni di S. Filippo, at the 

 foot of S. Fiore, confift likewife in this tufo and its various 

 jncruftations. Profeflbr BaldaJJari at Siena told me of a na- 

 tural white and downy fait. This he confiders as a concen- 

 trated and compaft, or rather congelated, vitriolic acid (oleum 

 vitrioli glaciate naturale), entirely pure and free from any 

 phlogifton. Filtering the hot water through red brazil-wood 

 the tufo gets by it a fine red colour. If it be precipitated in 

 glafs- mouldings or forms, itsfurfaceis extremely fmooth and 

 fplendent. By thefe principles they make not only impref- 

 fions of medals, but likewife of greater bas-reliefs ; which, 

 refembling to marble-work, are even fuperior to them on 

 account of the finer colour. Mr. Vegni has fucceeded already 

 in calling bufls of this tufo, and he foon hopes to cafl ftatues 



