542 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



A study was made of a number of difTorent species to determine 

 the specific gravity of the actual wood substance. Results obtained 

 tlius far show it to be from 1.5 to 1.(5, the variation among species 

 being comparatively small. There are indications, however, that 

 it may be influenced by certain treatments. 



Tn the tests to determine the specific heat of wood, the chief results 

 of which were mentioned last year, a decided rise in temperature 

 with the absorption of water by the wood was indicated, and other 

 tests will be made to determine the extent and significance of this. 



The study of jihysical properties is not confined to the projects 

 just described. Information on such properties as specific gravity 

 of the oven-dry wood and shrinkage was obtained in connection with 

 the strength tests; transmission of moisture from the wood was 

 necessarily taken into account in kiln-drying experiments, while 

 special studies of the transmission of heat and pressure and of the 

 permeability of woods were carried on in connection with wood- 

 perservation work. 



DRYING OF WOOD. 



A new type of kiln, invented by Mr. H. D. iiemann, a member 

 of the laboratory staff, has proved a success experimentally, and 

 two patents covering the principles of its operation were received 

 in March. These patents were dedicated to the public. The efficiency 

 of the method in commercial practice has been tested at Berkeley, 

 Cal., and at the Madison laboratory. The kiln at Berkeley has 

 been used to dr}'^ eucalyptus lumber. It was operated during the fall 

 and winter with blue gum {Eucalyptus globulus) and manna gum 

 {EiLcalyptus viminalis), and worked admirably. A small number of 

 excellent boards were turned out, the material having been dried 

 from the green condition with practically no checking or honey- 

 combing, a thing which so far as known has never before been accom- 

 plished. The practical impossibility, however, of obtaining green 

 lumber from young trees which is neither w^arped, checked, nor 

 curled makes it very doubtful whether trees of these two species 

 under 30 or 40 years of age, such as constitutj© the greatest part of 

 the present stand of eucalyptus in California, can profitably be con- 

 verted into high-grade lumber. It seems probable, however, that 

 other eucalypts of slower grow^th may produce valuable lumber in 

 from 30 to 40 years, and experiments will be made wath several of 

 them if trees can be found sufficiently^ mature for the purpose. 



The kiln at Madison is a small w^ooden one. A number of runs 

 have been made with green wagon stock, chiefly of swamp-grown 

 red and white oaks, and birch, with results that indicate a great possi- 

 ble saving over present practice by elimination of checking and reduc- 

 tion of the time required for drying. A third kiln, at Cairo, 111., 

 will be used for drying hickory vehicle stock. 



A study of the drying of lumber at atmospheric pressure, carried 

 on in the experimental kiln described last year, brought out the need 

 in kiln operation for accurate control of humidity and temperature, 

 combined with a large amount of air circulation. In connection with 

 this study a humidity diagram was prepared for the use of dry-kiln 

 operators in determining all conditions of humidity within the kiln. 

 A field study of commercial practice in the kiln drying of Douglas 

 fir and other northwest woods was made during the year. 



