398 



THE AGRICULTURAL NEWS, 



Devembee 9, lyiL 



FUNGUS NOTES. 



THE ROTTING OF TIMBER AND ITS 

 PREVENTION. 



It is a well-known fact that all kinds of timber, when 

 they are exposed unprotected for any length of time to the 

 action of the weather, gradually decay and become useless. 

 This is particularly observable in tropical countries with 

 a heavy rainfall, though it occurs also, and to an equal extent, 

 in temperate climates, the diflference being that the rate of 

 decay under the drier, cooler conditions is not as rapid. The 

 rotting is usually attributed, in a vague way, purely to the 

 action of the weather, but in reality it is due primarily to two 

 sets of definite cause.s, namely, fungi and insects. In tem- 

 perate countries, the former are probably the more important, 

 but in the tropics the latter are at least of equal moment, 

 owing to the occurrence there of the different species of wood- 

 destroying ants. 



The attacks of the numerous forms of timber-destroying 

 fungi are directly dependent upon two important factors — the 

 presence of moisture and free access of air; while their rate 

 of growth is influenced by the quantity of moisture usually 

 present, and by the prevailing temperature. Timber that is 

 exposed freely to the air, Imt is only wetted by moderate 

 rains, and is usually practically air-dry, does not as a rule rot 

 rapidly, since the water-supply, particularly within the 

 timber, is insufficient for the growth of the destroying fungi. 

 That this is the case is shown by the comparatively long life 

 of the upper parts of telephone posts, or of gate posts, in all 

 but very damp localities. Again, timber will not rot under 

 damp conditions when air is excluded, as is shown by the 

 fact that planks stored in water last better than those kept 

 in any other way. These factors are of far less importance 

 in the case of insect attacks, especially those of wood ants. 



One other important matter, infiuencing the occurrence 

 and rate of rotting of timber, is the thoroughness with which 

 it is seasoned. Badly seasoned timber is damp internally, 

 and thus affords a possibility of growth to fungi that would 

 be unable to live on really dry wood. Furthermore, such 

 timber contracts and expands unevenly with the changes in 

 temperature of the surrounding atmosphere, so that larger and 

 more serious cracks form in it than appear in well-seasoned 

 wood. These cracks afford a means of entrance for insects 

 and fungi, and often negative the effects of protective treat- 

 inent.s, when they appear after such have been applied. The 

 reason for this will be explained below. 



Since both moisture and air are neces.^ary for the growth 

 of wood-destroying fungi, it is natuial that timlur should decay 

 most rapidly in that part immediately above the point where 

 it comes in contact with the soil. Thu.s, posts of all kinds 

 that are burie<l in the soil are liable to rot through the foot or 

 two of their length that is immediately above the soil surface. 

 The wood in this part ab.sorbs moisture continually from the 

 earth, while there is also free access of air to it. The portion 

 higher up is dry, while that in the soil receives but little air. 

 For a similar reason, railway sleepers are rapidly destroyed 

 when unprotected. Other timbers that do not come in contact 

 with the earth are far less quickly disintegrated by fungi, 

 £xcept where the rainfall is very heavy, and fairly uniformly 

 distributed throughout the year. The sanu' does not apply 

 to the attacks of insects, especially wood ants, since they may 

 be found in any timber, however dry. 



In order to reduce the loss occasioned by the rotting of 

 wood, that is to prolong its period of service to the 



greatest possible extent, use is made of various substances 

 that are poisonous or distasteful to insects, and poisonous to 

 fungi. The.se are always employed in the liquid form and 

 are either applied to the surface or made to penetrate the 

 wood itself. Examples of the first class of substances are 

 paints and varnishes, and of the second various solutions of 

 chemicals such as bluestone (copper sulphate), zinc chloride, 

 and corrosive sublimate and liquids such as heated creasote, 

 heated tar, andcarbolineum preparation. There are also others, 

 some of which will be mentioned below. 



In either of the classes of treatment just mentioned, the 

 object aimed at is to cover the timlier with a protective skin 

 that shall completely enclose the inner substance. In the 

 first case, this skin is composed of the paint or varnish itself; 

 inthe second it consists of the outer layers of the wood, which 

 are rendered poisonous by the presence in them of the perme- 

 ating comi)ounds. The superficial nature of such treatment 

 makes it ea.sy to see why splits in timber that occur after it 

 is treated defeat the object of the treatment. 



There are .•■everal methods of applying permeating wood 

 preservatives. The most elementary is hand application, 

 with a bru^h. The penetration obtained by this means is 

 poor, and the method is expensive when it is employed on 

 a large scale. "Another method, especially applicable to 

 posts or poles whose butts alone need be treated under 

 ordinary conditions is, as is explained above, to stand them 

 upright in suitable ^anks of the liquid, most generally cold 

 creasote, where they are left until they are well permeated. 

 In dealing with creasote, and indeed with many other 

 substances, an extension of this method is found to give 

 better results. The wood is immersed for two or three 

 hours in hot liquid, and then transferred to a tank 

 containing cooIct liquid, or the original liquid is allowed 

 to cool over night. Tlie heating drives out some of 

 the air and moisture in the wood: so that when cooling 

 commences the liquid enters to take their place. An even 

 more elaborate system depends on forcing the preservative in, 

 under pressure. The wood is placed in a closed chamber, 

 which is partly exhausted of air. Hot preservative is then 

 allowed to enter, and the pre-jsure is increased. Such 

 a method ensures good penetration, but requires an expen- 

 sive plant, and is impracticable on most tropical estates. Of 

 the liquids used as preservatives creasote is that most com- 

 luonly employed. Various carbolineum compounds, such as 

 Carbolineuin Avcnarius are, however, frequentl)' used, as 

 well as others. A new preparation has lately been put 

 forward, namely Cresol-Calcium which consists mainly of the 

 calcium salts of certain tar acids obtained from > r.'asote. 

 These are soluble in water (sec Af/iicid/ura/ Xeirf, X.,\. IX, 

 p. 137). A somewhat diU'oront method of preserving wood 

 is the l^iwell i)roces^, in which green wood is boiled in 

 a solution containing C>0 jx'rcent. of molasses, allowed to cool 

 in the liquid, iind finally dried in specially constructed 

 chambeis. Further particulars of this are to be found 

 in the AqricuKural X'H'S, Vols. VIII, pp. 2-49 and 408; 

 and IX, p. 201. 



The primary advantage derivab'c from the u.se of pro- 

 tcctives for timber of all kinds is that its period of useful- 

 ness is doubled or even trebled; while the cost of treatment, 

 though far from negligible, is considerably less than that 

 involved in replacing decayed structures made of unprotected 

 wood. In India and in other parts of the tropics, protection 

 of some sort is practically essential for all wood-woik in 

 hou.ses on account of the attacks of termites, and it is probable 

 that much money could be saved in the West Indies if timber 

 was rendered less liable to dsstruction by wood ants, liail- 

 way sleepers, and telephone and electric power posts are regu- 



