* 
Ws 
° 
; ‘Method of checking Decay in Trees. 307 
* Other experiments have proved the prefence in this mi- 
neral of filex and alumine; fo that C. Vauquelin and Taflaert 
believe it to be compofed of the following fubftances : 
Chromic acid - - 43 
Oxyd of iron ~ - a4ry 
Argil = - = 203 
Silex - - -— 2 
_ They ate of opinion alfo, that, the chromic acid being in 
fuffictent quantity to faturate the oxyd of iron, this araetal 
is a triple combination of the chromic acid, the oxyd of 
iron, and argil. 
8. The oxyds of chrome, er the chromic acid, may be 
employed in the porcelain manufaéture. When pure, they 
give an emerald green, more beautiful than that of copper ; 
and, mixed with lead or antimony, a canary-bird green. 
They may be employed alfo in painting, by feparating the 
acid from the iron, and combining it afterwards with differ- 
ent metallic oxyds by double affinities. 
METHOD OF CHECKING DECAY IN TREES. 
The chefinut lives a long time, and often attains to an 
‘extraordinary fize; but unfortunately the texture of its wood 
alters under certain circumftances: it becomes foft, falls 
_ into duft, a cavity 1s gradually formed in the heart of the 
tree, and this cavity, by the progrefs of the decompofition, 
becomes fti!l larger; fo that, at laft, the trunk feems to 
tonfitt of nothing but bark ; and being too weak to fupport 
the branches, and refift the violence of hurricanes, it cannot 
Jong exift. It is by fimilar changes and decompofitions of 
the ligneous principle, that trees, which have been: growing 
for ages, are feen to perifh in a very little time. 
C. Chaptal, in travelling through different parts of France, 
and particularly the Cevennes and the department of Allier, 
ebferved, that a great number of cheftnut-trees were hollow, 
and charred over the whole internal furface.. He was told 
by the inhabitants of the country, that this procefs was em- 
ployed to ftop the progrefs of the caries, which otherwife 
would deftroy the whole tree. When they obferve that this 
Rr 2 difeafe, 
