418 SECTIONAL TRANSACTIONS.— K*. 



density, rate of growth, percentage summerwood and moisture content and produced 

 results which, while having some application in problems of design, produced strength 

 values which could be quite misleading, and become dangerous when published as 

 general engineering tables on strength of timbers. Engineers or architects in using such 

 tables were confronted with the possible alternatives of loss in efficiency or loss in 

 «conomy in their designs. 



The modern methods described are those originated at Madison, Wisconsin, and 

 through the co-operation of Canada, India, and other parts of the Empire became an 

 international code for obtaining comparable strength values of timber grown in the 

 different countries. 



The need for material with a complete history beginning in the forest was empha- 

 sised, and this was followed by a general outline of the procedure of tests, including 

 collecting the material, preparing and sawing the logs, and testing the specimens. 



It was pointed out that the tests are designed to determine the inherent fibre- 

 strength with relation to the natural characteristics. The variable of moisture content 

 is eliminated by first testing the timber green and again when dried to a uniform 

 standard moisture content of 12 per cent. The comparison of the relative strength 

 values of the different species indicates their values as mechanical timbers. It was 

 explained that the results of these tests on clear material form the basis for the study 

 of the influence of defects in structural sizes, leading to systematic grading. 



Over 3,000 tests on clear material of home-grown timbers have been done since 

 the work began in the Timber Research Laboratory in April of this year. No work 

 on the influence of defects will be done until some time later, when the tests on the 

 small clear specimens are well advanced. Tests on the comparative strengths of home- 

 grown and imported pit-props are being carried on, and several minor investigations 

 on the strength of manufactured articles are in progress. 



The work already begun at the Forest Products Research Laboratory, Farnborough, 

 Hants, will be continued, and extended when the laboratory is transferred to its 

 permanent site at Princes Risborough. 



19. Mr. S. T. 0. Stillwell.— TAe Seasoning of Timber. 



After a brief introduction the seasoning process was described under two headings, 

 the first of which concerns the moisture in the wood itself, and the second the necessary 

 factors external to the wood. 



So far as the moisture in the wood is concerned, it was shown that the difficulty 

 of seasoning is due to a shrinkage of the structure which takes place as certain of th» 

 moisture dries out, together with the fact that moisture does not move freely from 

 pomt to point inside the timber itself. 



To obviate this difficulty it is necessary, in seasoning a piece of timber, to limit 

 the rate of evaporation from its surface to correspond approximately with the rate 

 of moisture movement from the interior portions to the surface. 



Exterior to the wood, three factors are involved. Firstly, heat, which is taken 

 from the surrounding air, is necessary to evaporate the moisture in the wood. 

 Secondly, the temperature and humidity condition of the surrounding air determines 

 the rate at which evaporation from the wood surface takes place. Thirdly, a 

 circulation is required to ensure continual replacement of air which has given up 

 heat and taken up moisture in drying the wood, so that the process may proceed 

 continuously. 



In considering the application of these factors in practice, it was sho^wn that in 

 air-seasoning conditions, the temperature and humidity of the air is variable and 

 uncontrolled. The rate of drying, therefore, can only be regulated in a rough fashion 

 by means of sheltering and other expedients. In temperate climates, however, the 

 rate of drying is at most comparatively slow, and it is on this account rather than 

 from precision of control, that serious damage is avoided. The necessity for circula- 

 tion influences the form of pile, and not only is it necessary to build the boards with 

 transverse sticks between each layer, but it is best to limit the width of the pile in 

 the direction in which the air travels. It is also good practice to raise the pile well 

 above ground level, and to provide good ventilation of the space below it. 



In kiln-seasoning, the same factors and conditions enter into the drying process. 

 At the higher temperatures of the kUn the internal moisture movement is more rapid, 

 but the surrounding air has relatively greater evaporative powers, so the necessity 

 for control is greater. 



