IMSBMilKtitWi^iil C' 



The Penetrability of Wood 



The preservation of timber by impregnating it with various anti- 

 septics is now well established in this country. One of the important 

 problems connected with the treatment has to do with the differences 

 in the penetrability exhibited not only by woods of different species, 

 but also by individual specimens of the same kind. There is consider- 

 able divergence of opinion as to how far it is practicable to attempt 

 to group ties and other material for each charge of the retort. On 

 one point, however, operators are generally agreed, namely, that much 

 better results are obtained when the timber treated is well seasoned. 

 When wood becomes dry its penetrability by both gases and liquids 

 is increased to a decided extent. The same piece of white oak which 

 will, while green, effectually withstand an air pressure of 150 pounds 

 per square inch, will, when dry, allow the passage of air, not only 

 through the vessels but also the other elements, under a pressure of 

 five pounds or less. According to the theory of Mr. Tiemann and 

 other investigators of the Forest Service the explanation of this is 

 that the drying of the cells causes minute checks or slits to occur 

 in the cell walls, thus allowing free passage from one cell to an- 

 other. The drier the wood becomes the larger are the slits and 

 the more permeable the wood. These slits do not entirely close 

 when wood is soaked, so that wood once dried cannot be restored 

 to its original condition of impenetrability. 



Since it is possible to observe these slits under a microscope, 

 and as their presence explains satisfactorily many of the phe- 

 nomena of drying, Tiemann 's theory has been generally accepted 

 as correct. In a recent issue of the Forestry Quarterly, however, 

 Mr. Bailey of the Harvard School of Forestry publishes the re- 

 sults of his investigations on the subject. While in some points 

 he verified the findings of the government experts, on the whole 

 he attempts to disprove their conclusions and offers a different 

 explanation for the increase in penetrability incident to drying. 

 He found, for instance, that spiral cracks in the -walls of tra- 

 cheids and fibers occur in only a small percentage of dry wood, 

 and that when present in softwoods are confined to the heavy, 

 thick-walled cells at the end of the year's growth. The most im- 

 portant finding, however, is that these cracks do not extend entirely 

 through the cell walls, but are confined to the thickened portion of 

 it, the original or primary cell wall remaining intact. It is this 

 wall which completely surrounds every cell and separates it from 

 its neighbors, preventing the passage of heavy oils and of undis- 

 solved gases. It is here that the two theories come in conflict, 

 since the government investigators held that the checks extended 

 through the primary wall as well as through the thickened portions. 

 It is also claimed in this paper that in some longleaf pine 

 paving blocks examined, when the penetration of the creosote was 

 confined largely to the dense bands of summerwood, the walls of 

 the cells composing the latter were in the majority of cases found 

 to be unruptured. It is further stated that air passes as easily 

 through dry cells whose walls are unruptured as through cells 

 whose secondary walls have been cracked in drying, while in many 

 cases air cannot be passed through dried cells whose secondary 

 walls possess well developed slits or cracks. From these tests the 

 writer of the paper concludes that Tiemann 's hypothesis regard- 

 ing the effect of the slits cannot account for the penetration of 

 gases and oils into seasoned wood. 



How then is the known increase in penetrability to be explained? 

 It is very evident that some change must have been made in the 

 wood. It is well known that conifers or softwoods are composed 

 largely of minute fibrous cells with closed ends, and are devoid of 

 open vessels such as occur in hardwoods. Liquids in passing 

 through these closed cells travel primarily in the cavities of the 

 cells and pass from one to another by means of delicately con- 

 structed valves or bordered pits in the cell walls. It has always 

 been supposed that the membranes of these bordered pits were 

 entire. The pit membrane is merely a portion of the primary cell 

 wall which has not been thickened, thus leaving a thin place 



—24— 



through which water could filter. The pit is the thin spot, and as 

 the thickened portion grows out over it to some extent it gives 

 the appearance of a border, hence the name bordered pit. 



According to this article the membranes of the bordered pits are 

 not always entire, but possess numerous minute perforations whose 

 presence may be demonstrated by careful microscopic examination 

 and by experimental means such as passing through green sapwood 

 water containing very fine particles of carbon held in suspension. 

 The particles passed through without diflSculty. 



The investigator concludes that when wood is thoroughly dried 

 no structural modification, such as the rupturing of the cell walls, 

 is essential in order to account for the penetration of gases and 

 preservatives into seasoned wood; but that whenever preservatives 

 are injected rapidly into green or seasoned wood, the penetration 

 takes place primarily through the cavities of the cells, and the 

 preservatives pass from one cell to another through the bordered 

 pits. In green wood the bordered pits and membranes are com- 

 paratively impermeable to undissolved gases and to oils > and other 

 heavy or viscous liquids. This is largely due to the fact that the 

 pit membrane is saturated with water, the surface tension of 

 which resists the gases and liquids, except in water solutions. Dry- 

 ing not only removes the water from the pit membranes but also 

 in some cases ruptures them, which accounts for the fact that 

 resoaked dry wood is less impervious to air than green material. 



K. C. D. 



Plain Oak in Furniture 



There are indications that plain oak is to have quite a run in 

 high-grade furniture. It has been featured for some time in 

 office furniture. Very attractive samples of plain oak furniture 

 in natural finish have been displayed in show windows, and there 

 is some speculation in furniture circles as to how far this idea may 

 extend, and as to whether or not it will immediately become a 

 strong feature in the high-grade furniture trade. 



Plain oak has suffered considerably from neglect for a good 

 many j'ears and it really has an inning due it in the furniture 

 trade, not merely in the cheaper and less pretentious furniture, 

 but also the high-grade furniture that is well finished. The plain 

 oak office furniture that has been shown exhibited a quality of 

 workmanship and finish that made it very attractive, and it fur- 

 nishes evidence, were evidence necessary, that plain oak is good 

 material for the finest kind of furniture, and will take on a finish 

 that makes it show off well in the best of company. 



For the past four or five years, or perhaps longer, quartered 

 oak, mahogany, Circassian walnut and gum have vied with each 

 other so much in the furniture trade and have been objects of so 

 much concentrated attention that plain oak has been neglected 

 untU the plain oak product has practically disappeared from first- 

 class furniture stores. It is getting attention now and it is in 

 such condition in this relation to furniture manufacturers that the 

 present may well be regarded as a psychological moment for boost- 

 ing and pushing plain oak. The furniture trade itself is ripe for 

 it, and is in a more or less speculative mood as to how the public 

 will take to it if it is used in the better designs of furniture, 

 and properly finished. As the case now stands, it looks as though 

 all that is needed to create a boom in plain oak in the furniture 

 trade is a bit of judicious boosting and exploiting and due care 

 on the part of the furniture manufacturers in the uses to which 

 they put it that they may not kill off its rising popularity with 

 something freakish and unsightly in design. 



Every man that has ever made oak lumber or has worked it into 

 furniture should know without being told that it is a great cabinet 

 wood, and has many elements of beauty not found in other woods. 

 It is a wood that belongs in the best classes of woodwork, whether 

 it be in the furniture or in interior trim. 



