140 Mr. Knight on the office 
Pieces of the external, or last formed layer of the albur- 
num, and of the heart wood, were taken from the trunk (near 
the ground) of an oak of forty years old, and of very vigo- 
rous growth, in the first week of December. These were 
slowly dried in a temperature not exceeding at any time a 
hundred and twenty degrees ; under which circumstances 
1000 parts of the alburnum lost 4 6g parts, and an equal 
quantity of the heart wood 500 parts, or precisely half its 
weight. Upon the 24th of April, similar pieces of the albur- 
num and heart wood were taken from the same tree, and 
dried in the same manner ; when 1000 parts of the alburnum 
lost in drying 532 parts, and an equal quantity of the heart 
wood 307 parts. 
The alburnum and heart wood of a poplar tree of about 
80 years old were subjected to similar management in 
December ; when 1000 grains of the alburnous substance 
lost 335 grains, and an equal quantity of the heart wood 626 
grains. On the first of March, 1000 grains of alburnum 
being taken from a tree of similar age and habit with the 
preceding, lost in d i-ying 337 grains ; and the same quantity 
of heart wood 684 grains. Not only the cellular substance 
of the heart wood, but the tubes also, which are usually quite 
empty in the alburnum, were perfectly filled ; so that the 
heart wood of the poplar exhibited nearly the semi -transpa- 
rency of horn ; and in subsequent experience I have found 
that it contains nearly the same quantity of water in every 
part of the year. 
This abundant fluid in the heart wood was some years ago 
first observed by M. Coulomb, when felling poplar trees iti 
