7 
68 On Porcelain, and the nutritive Use of Lichen iskandicus. 
riment proved to us Article [. Part IL. edly, That the 
more we reduce the friction of the regulator the nearer we 
approach to the compensation, of which we have spoken in 
the second observation. 3dly, That by the preceding we 
are very distant from this compensation in common watches 
with a dead escapement. 
[To be continued.] 
X. Extract of a Letter from M. Proust to M. Vau- 
QUELIN, wpon Porcelain, and the nutritive Use of the 
Lichen islandicus*. 
Madrid, Dec. 22, 1805. - 
W: have been to visit the porcelain manufactory of 
M. Sureda, who makes the finest biscuit china I have ever 
seen. He does not make use of kaolin, however, but of a 
siliceous-magnesian stone called sea-froth or lithomarga, 
found at the gates of Madrid +. We shall send you some 
specimens which must astonish you. M. Sureda covers 
Kis china with feldspars of Galicia, which are very elegant.. 
You may regard the above kind of stone as one of the best 
for making chemical furnaces. When it comes out of the 
quarry it is shaped like soap wedges. The lightness of these 
furnaces is extraordinary; and they never melt, however 
strong the fire may be raised. Besides’ magnesia, silex, and 
some atoms of argil and lime, this stone contains a little 
potash, which cuntributes not a little to the beauty and fine+ 
ness of tlie china. 
I have now to mention a fact perhaps as interesting as 
the foregoing. Don Mariano la Gasca, a student of Cava- 
nilles, and a young botanist of great promise, has sent me @ 
quantity of lichen islandicus, which he discovered in the 
mountains of Leon, where it grows in great abundance. 
I expected to have only found a more or less tinc- 
torial substance ; but I found that it was an excellent plant 
for eating when it was cooked, very tender, and that it 
* From Annales de Chimie, cone Ivii, p. 199. 
+ For a memoir on this substarice, see Philosophical Magazine, vol. iii. p. 165. 
ought 
