240 LECTURE XIV. 



Other methods, I succeeded in doing this in the following manner: — Since it is 

 impossible to fill all the cavities in a large piece of wood with water, cross slices 

 0-I-0-2 millimetre thick were taken of the wood of Firs and ordinary foliage trees : 

 since now the wood cells are several millimetres long, all the elements in these cross 

 slices must be opened and cut through transversely. They were then boiled for a long 

 time in salt solutions, to remove any bubbles of air. These solutions were of calcic 

 nitrate and zinc nitrate. The result was that the cross slices mentioned sank in such 

 solutions, though extremely slowly, when the areometer indicated a specific gravity of 

 1-56. This number thus expresses almost exactly the specific gravity of the wood cell- 

 walls ; or, in other words, if one had a cubic centimetre consisting entirely of the substance 

 of the wood cell-walls, it would weigh 1-56 gramme, whence results immediately that 

 one gramme of wood cell-wall occupies a space of o'64i cubic centimetre. Furnished 

 with this number, it is easy now to calculate in any piece of wood cut from a living 

 tree how large the spaces occupied by the lignified walls, by the water, and by the 

 cavities filled with air must be. First is determined the volume and the weight of 

 the fresh wood; it is then dried at 100°, and the weight of the dry wood determined. 

 The difference in weight obviously gives the weight of the evaporated water, from 

 which its volume follows immediately, since one cubic centimetre of water is exactly 

 one gramme. The specific gravity of the wood found above now allows us to 

 calculate from its absolute dry weight the volume of the cell-walls, since we divide 

 that weight by the specific gravity, and all else follows. To illustrate this by an 

 example — a cylindrical piece of wood, consisting of five annual rings, was taken from 

 the stem of a living Fir on the 2nd of January: the piece was 105 millimetres long 

 and 33 millimetres thick. From these dimensions the calculated volume is 89*8 

 cubic centimetres, and it was found, by immersion in mercury, to be 90 cubic centi- 

 metres. That the wood, though containing much water, still contained air, was clear 

 at once from the fact that it floated in water. 



Weight of the fresh wood 87-60 grammes. 



Weight of the dry wood 34'83 grammes. 



Water in the fresh wood 52"77 grammes. 



From the dry weight of the wood we get ~ = 2 2'33 cubic centimetres as 



the cubic contents of the cell-walls. ^ 



From these data it is calculated that 100 cubic centimetres of fresh wood 

 consist of — 



24-81 cubic centimetres = mass of wall (calculated dry). 

 58-63 ,, = water (in the cavities, and imbibed). 



16-56 ,, = air cavities. 



Since intercellular spaces and vessels do not exist in the wood of the Fir, the 

 16*560/0 air cavities were thus contained in the wood-cells themselves ; and since the 

 wood-walls, as we shall see, absorb by imbibition only about half their volume of water, 

 they thus contained only 12*4 cubic centimetres of water, the remaining water (viz. 

 46-23 cubic centimetres) must have been contained in the cell-cavities. 



