386 



FORESTRY INVESTIGATION* U. S. DEPARTMENT OF AGRICULTURE. 



Some of the disks were split to a wedge shape from center to periphery, so that each smaller 

 piece uot ouly represents a certain period of growth in quality, but also in quantity, thus simplify- 

 ing the calculations for the entire piece or disk. Other pieces were left in their prismatic form, 

 when to calculate the average density of the entire piece the density of each smaller piece is 

 multiplied by the mean distance of this smaller piece from the center, and the sum of the products 

 divided by the sum of the distances. 



Each piece is marked, first by the number of the tree, in Arabic; second, by the number of 

 the disk, in Roman numbers; and if split into small pieces, each smaller piece by a letter of the 

 alphabet, the piece at the periphery in all cases bearing the letter a. Besides the number and 

 letters mentioned, each piece bears either the letter N or S, to indicate its orientation on the north 

 or south side of the tree. To illustrate: 5 vii N a means that the piece bearing the label 

 belongs to tree 5 and disk vii comes from the north side of the tree, and is the peripheral part of 

 this disk piece. From the collector's notes the exact positiou of this piece i n the tree can readily 

 be ascertained. 



The entire prisms sent by freight are left in the original form, unless used for special purposes, 

 and are stored in a dry room for future use. 



WEIGHING AND MEASURING. 



The weighing is done on an apothecary's balance, readily sensitive to 0.1 gram with a load of 

 more than 200 grams. Dealing with pieces of 200 to 1,000 grains in weight, the accuracy of weigh- 

 ing is always within 1 gram. 



The measuring is done by immersion in an instrument illustrated in the following design : I" is 

 a vessel of iron; 8 represents one of two iron standards attached to the vessel and projecting 



FIG. 104. Apparatus for determining specific gravity. 



above its top; B is a metal bar fasteiied to the cup A, which serves as guard to the cup and pre- 

 vents it going down farther at one time than another by coming to rest on the standards S. The 

 cup A dips down one-sixteenth to one-eighth of au inch below the edge of the knee-like spout. In 

 working, the cup is lifted out by the handle which the bar B forms, water is poured into the vessel 

 until it overflows through the spout, then the cup is set down, replacing the mobile and fickle 

 natural water level by a constant artificial one. Now the instrument is set, the pan P is placed 

 under the spout, the cup is lifted out and held over the vessel, so that the drippings fall back into 

 the latter, the piece of wood to be measured is put into the vessel and the cnp replaced, and pressed 

 down until the bar B rests on the standards S. This is done gently to prevent the water from rising 

 above the rim of the vessel. This latter precaution is superfluo us where the cup fits closely, as it 



