July 



1919 



HARDWOOD RECORD 



19 



Chestnut ^s Characteristic Grain 



TWO TYPICAL CHESTNUT TREES 



That on the left with spiral grain grew from the seed, and the other 

 with straight grain originated in a sprout. 



Few woods have grain more characteristic than chestnut 's, but 

 nsually the grain adds little to the value of the wood, because it is 

 not very attractive. It is coarse and common in appearance. 



Two distinct grains occur in this timber, straight and spiral. If 



the wood is spiral, the bark is nearly always spiral also, running 

 round the trunk like a winding stair. This characteristic makes it 

 possible for a person walking through a chestnut forest to pick 

 out the straight-grained and the spiral-grained trees without making 

 many mistakes. The entire stand is divided in the two classes. 

 Trees of no other species show this peculiarity in so high a degree. 



Whether the grain of a chestnut tree is to be straight or spiral, 

 seems to be determined very early in the tree's history. Apparently, 

 it depends upon whether the tree originates in a seed or in a sprout. 

 The seedling produces the spiral grain, the sprout's grain is straight, 

 in most cases, at least, and when the kind of grain has once been 

 determined, it never afterward changes. A tree centuries old betrays 

 its origin, whether it came from a nut or from a sprout. At any 

 rate, it is believed that such is the case. Why it is so, is a question 

 not yet answered. 



It has been many times observed that very old and very large 

 chestnut trees usually possess the spiral grain. That fact has been 

 used as an argument to prove that the grain changes as age comes 

 on, and that what was straight in a tree 's youth becomes spiral as the 

 period of decline approaches. 



The facts do not warrant the conclusion, though it is usually true 

 that in a young chestnut stand a majority of the trunks have str^iglit 

 grain, while in a very old forest, the spiral individuals out-numbcr 

 the others. 



The explanation ought to be sought in the fact that trees which 

 spring from seeds (spiral) live longer than sprouts (straight); and 

 in the course of time the higher death rate among the sprouts lessens 

 their number uutil those remaining in old age are fewer than the 

 others. There is no proof that a tree vrith straight grain ever becomes 

 spiral. 



Warping of Aircraft Propellers 



One of the greatest troubles experienced with airplane pro- 

 pellers during the war was caused by the warping and twisting of 

 the blades near the tips, and a large percentage of the propellers 

 received at the front were rejected on this account. 



In order to determine the causes and to develop methods of 

 preventing this trouble, a number of experimental propellers were 

 manufactured for the War and Navy Departments by the Forest 

 Products Laboratory at Madison, Wis. 



The propellers were made of Central American and African 

 mahogany using carefully selected stock uniform in density and 

 moisture content, and were stored under uniform atmospheric con- 

 ditions for thirty days between the roughing out and final carving 

 operations. After the standard finish, consisting of five coats of 

 spar varnish, had been applied, they were again stored under the 

 same conditions for observation as to warping and twisting. 



These propellers were made up and handled much more care- 

 fully than the commercial product, and every possible effort made 

 to produce perfect results. After exposure to a very damp or 

 humid atmosphere for three or four months, it was found that 

 every propeller had warped or twisted or otherwise changed shape 

 to an extent that made them unacceptable for use. They had all 

 absorbed about five per cent of moisture through the five coats 

 of spar varnish, and this moisture caused all the trouble. The 

 treatments to which these propellers were exposed, namely, being 

 manufactured in a relatively dry condition and later exposed to 

 moist atmosphere, is very similar to that which is normally re- 

 ceived by propellers made in the United States and shipped to 



France. Frequently propellers are made in a relatively moist 

 climate and shipped to a drier one, and trouble from change of 

 shape due to drying out is almost sure to result. 



There is only one way in which trouble from change of shape 

 due to changes in moisture may be obviated, and that is to prevent 

 these moisture changes. The experiments just outlined show that 

 it is impossible even under ideal manufacturing conditions to 

 produce propellers which will not warp or twist with changes in 

 moisture. 



These changes may be prevented either by applying a moisture- 

 proof coating or by keeping the propellers under uniform atmos- 

 pheric conditions throughout their life. At present, the aluminum 

 leaf coating developed by the Forest Products Laboratory is the 

 only practicable moisture-proof coating which has been successfully 

 applied to propellers. It is not possible to keep propellers under 

 absolutely uniform atmospheric conditions during manufacture 

 and service, but these conditions can be approached by making up 

 the propellers at the moisture content which they will normally 

 reach in service. Propellers made up this way and coated with 

 aluminum leaf have the best possible chance of giving high eflS- 

 eiency and long service. 



Poison sumac and poison ivy should not be confused. They are 

 wholly different though closely related in plant kinship. Poison 

 sumac is a bush or tree and looks much like any other sumac; but 

 poison ivy is a vine that may be on the ground and send up short 

 branches, or it may climb trees, rocks; or walls. 



