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Journal of Agricultural Research 
Vol. II, No. 6 
which observed results depend on wood substance and on air space is 
calculated. The porosity of wood, then, is an important item in the 
study of its heat conductivity. 
The porosity of wood is also of importance directly in the practice of 
impregnating wood with preservatives, since the capacity of the cavities 
fixes an upper limit to the quantity of preservative which may be injected. 
PREVIOUS INVESTIGATIONS 
The first published statement of the density of wood substance appears 
to be that of Hofmeister, 1 who assumed a density of at least 1.45. His 
assumption was based on measurements of the density of flax fibers, 
which have a very small lumen. Subsequently other writers assumed 
a density of 1.55. 
In 1879, Sachs 2 published a careful study of the density of wood sub¬ 
stance. By washing the air from wood in a current of water and then 
using Archimedes’s method, Sachs obtained a density of 1.5 for Pinus 
pumilo and 1.4 for Abies pectinata. Wood boiled in water to expel the 
air gave somewhat higher densities, and when washed in alcohol the 
results were still higher—viz, 1.523. 
Finally, Sachs suspended thin sections of wood, from 1/10 to 1/5 mm. 
thick, in solutions of calcium nitrate and zinc nitrate. The density of the 
solution was adjusted until the sections of wood sank very slowly. It is 
evident that when the wood remains suspended in the solution the two are 
of the same density. Sachs read his solution densities from a hydrometer. 
Sachs found no difference between determinations made with these two 
nitrates. He evidently experienced difficulty in reaching exact equilib¬ 
rium, and was satisfied when his sections sank very slowly through his 
solutions. He found that sections of Prunus cerifera and Populus dilitata 
sank in calcium nitrate solutions of 1.54 density, while Abies pectinata 
sank in a zinc-nitrate solution of 1.56 density. His results were not 
final, but were merely a somewhat closer approximation than any of his 
predecessors had secured. 
Three years later Hartig 3 determined the density of wood substance for 
five additional European species—viz, birch, beech, oak, spruce, and 
Scotch pine. He followed Sachs’s method, using calcium nitrate, and 
apparently met with greater success in establishing equilibrium between 
his solutions and the wood sections. He found the same value, 1.555, for 
the density of all five species. 
1 Hofmeister, Wilhelm. Ueber Spannung, Ausflussmenge und Ausflussgeschwindigkeit von Saften 
lebender Pflanzen. In Flora, Jahrg. 45 (n. R. Jahrg. 20), No. 7, p. 105, 1862. 
2 Sachs, Julius. Ueber die Porositat des Holzes. In Arb. Bot. Inst. Wfirsburg, Bd. 2, p. 291-332, 2 fig., 
1879. 
* Hartig, Robert. Ueber die Vertheilung der organischen Substanz, des Wassers und Luftraumes in 
den Baumen, und fiber die Ursache der Wasserbewegung in transpirirenden Pflanzen. 112 p. Berlin, 
1882. (Untersuch. Forstbot. Inst. Mtinchen. Bd. 2.) 
