PHILOSOPHICAL EXPERIMENTS OF THE ROYAL SOCIETY OF LONDON. 
line earths produce copious precipitates, 
carrying down almost the whole of the 
tannin, gallic acid; and extract. Alu- 
mine and the oxyds of tin and zine 
have a similar effect. The soluble mat- 
ter of 500 grains of galls, when the 
water was gently evaporated, amounted 
to 185 grains, of which 130 were tan- 
nin, 22 mucilage, 31 gallic acid and 
extract, 12 calcareous earth and saline 
matter. 
Catechu, or terra japonica, is the next 
substance treated of. The discovery of 
its tanning powers is owing to Sir Joseph 
Banks, who, from the taste, suspected 
in it the presence of tannin. Its habits 
with acids, earths, and alkalis, are ex- 
tremely similar to those of the infusion 
of galls. 200 grains of the purest Bom- 
bay catechu appear to contain 109 of 
tannin; 68 of peculiar extractive mat- 
ter; 13 of mucilage, and 10 of insolu- 
ble residue, chiefly sand and calcareous 
earth. 200 grains of Bengal catechu 
afforded 97 of tannin; 73 of extract; 
1c of mucilage ; and 14 of residue. 
In the astringent barks, the interior 
white bark contains the greatest quantity 
ef tannin, the middle or coloured part 
chiefly abounds in extractive matter, 
and the epidermis seldom contains either 
one or the other. 
An ounce of the entire bark of the 
chesnut yielded 53 grains of soluble 
matter, 21 of which were tannin. The 
same quantity of oak-bark yielded 61 
‘grains, of which 29 were tannin; and 
the Leicester willow furnished 71 grains, 
33 of which were tannin. 
. An ounce of elm: bark gave 13 grains 
of tannin. 
common willow 1} grs. 
— Sicilian sumach 78 grs 
———— Malaga sumach 79 grs. 
— souchong tea 48 grs. 
a ereen; tea 41 yrs. 
_ Of all substances catechu contains the 
greatest proportion of tannin, and jor 
the common uses of the tanner, one 
pound of catechu is equal in value to two 
and a half of galls, to seven and a half 
of Leicester willow bark, to eleven of 
Spanish chesnut, to eighteen of elm bark, 
twenty-one of common willow bark, and 
thred of sumach. 
11. Account of some Experiments on the De- 
scent of the Sap in Trees. By JV. A. 
Kynieur, Esq. 
Mr. Knight showed in a former paper 
that the sap of vegetables, after having 
895 ” 
been first absorbed by the bark of the 
root, passes into the alburnum of the 
root, trunk and branches; whence, by 
means of the central vessels, it arrives 
at the succulent part of the annual 
shoot, the leaf-stalkk and leaf, from 
which, through the returning vessels of 
the leaf-stalk, it returns into the bark. 
In the present memoir he resumes this 
interesting subject, and points out the 
principal causes which influence the 
formation of wood by the descent of the 
sap through the bark. . 
Motion, according to Mr, Knight, has 
a very striking effect on the circulation 
of the sap and consequent formation of 
wood. Of two young healthy trees 
similar in every other respect, if one is 
bound to a stake so as to prevent the 
motion of the trunk, without compress- 
ing the bark, and the other is left at full 
liberty to be blown about by the wind, 
it will be found that the trunk of the 
former will enlarge very slowly in dia- 
meter, in proportion to that of the 
former. If the tree, instead of being 
bound tight, is allowed to have motion’ 
in one direction only, the enlarged dia- 
meter of the wood will be principally in 
that direction; a horizontal section of 
the trunk presenting an oval instead of a 
circle: hence trees in exposed situations 
have the greatest part of the wood depo- 
sited in the trunk and large branches, 
while those in thick woods being in part 
deprived of motion in the trunk, and alse 
excluded from the light, the principal 
nourishment will be distributed to the 
branches and leading shoots: hence old 
trees whose bark is become rigid gene- 
rate little wood; but when the outer 
bark is removed, the motion and free 
communication being restored, a very 
rapid enlargement of bulk takes place, 
If Mr. Knight’s theory of the formation 
of wood be true, tuberous roots must 
also be formed of matter that has de- 
scended from the leaves through the. 
bark. In order to ascertain this, he 
took a potatoe-plant, and carefully divid- 
ing the runners, which connect the tuber 
with the parent plant, he immersed both 
the divided ends in a decoction of log- 
wood; at the end of twenty-four hours 
he found, that the coloured infusion had 
passed along the runners in both direc- 
tions, but that it had not entered the 
vessels of the parent plant, whereas the 
vessels of the tuber were almost com- 
pletely penetrated by this coloured in- 
jection. 
