152 



EXPERIMENTS UPON TANNING MATERIALS. 



of the lower parts of the trunk (up to 3 meters from the ground) is always greater 

 than it is above. 



11. The specific weight of green wood peeled, is always greater than when the bark 

 is on, and varies between 0.97 and 1.04, and the specific weight of the wood alone is 

 always greater near the ground than it is higher up. 



12. Green bark is always lighter than green wood. The specific weight of green 

 bark diminishes in proportion as the tree grows older. 



13. Bark dried in the forest is naturally specifically lighter than green bark, and this 

 also diminishes as the tree grows older. The facts stated in paragraphs 12 and 13 are 

 shown as follows : 



Specific weight. 



Glossy bark from the branches 



Average bark from the branches 



Glossy bark from trees 16 years old , 



Glossy bark from trees 24 years old 



Glossy bark from trees 36 years old 



Glossy bark from trees 55 to 62 years old 



Although the above experiments upon bark in its green state, or dried in the forest, 

 are of most importance, we should not neglect the conditions of bark dried in the open 

 air, and for this end the process was conducted as follows : 



From the various kinds of bark used in the preceding experiments, there was weighed 

 from six to eight kilograms that had been dried in the forest, and its volume was 

 ascertained. Each of the specimens, carefully labeled, were then collected and sent in 

 a sack to Hohenheim, and there kept irom the end of May, 1874, to the end of April, 

 1875, in a small house, upon planks, perfectly dry, and well exposed to the air. When 

 completely dry they were again weighed, piece by piece', on a warm, dry day, with 

 bright sunlight, and their value was ascertaiued with great exactness by a xylometer. 

 The results may be easily stated in a few points : 



1. Both "glossy" and "average" bark from the trunk lost, in passing from forest- 

 dried to exposure in open air, 4 per cent., and from the branches 5 per cent., of water.- 

 This is further shown in the first column of the next table. 



2. The change in volume in passing from the condition of forest-dried to drying in 

 the free air was much greater, while from green to forest-dried the percentage lost by 

 g een bark was much more than the relative loss of volume, the results being oppo- 

 site. The difi'erence which for forest-dried bark exists between the loss of weight and 

 loss of volume was found to be sufficiently compensated in its further drying in free 

 air, so that for the latter the volume agrees approximately with the percentage of 

 weight lost by evaporation. It disai>peais, in fact, in its passage from forest-dried to 

 full drying, the amount being shown in the second column of the following table : 



lis 



Ei:: 



-§52 



For glossy bark from the tmnk 



For aver.Tjie bark from the trunk 



For glossy bark from the branches. 

 For average bark from the branches 



',r cent 

 -16 

 36 

 54 

 50 



Percent 

 11 

 11 



19 

 20 



Per cent 

 51 

 3-2 



00 

 56 



3. The specific weight of the older " glossy bark" from the trunk (38 years), dried 

 in the free air, agrees very nearly with that'dried in the forest (0.74, instead of 0.75), 

 but young " glossy bark," on the' contrary, has a little greater density, it being 0.80 per 

 cent, at the age of 24 years, 0.86 per cent, at 16 years, and 0.83 for branches. In like 



