On The Testing And Strength Of Railway Materials, &C.

occupying the larger portion . All timber trees increase by addition to the external surface , and it therefore follows that the AVOOC ! of oldest growth is found in the centre of the tree , ancl that the several concentric layers are younger in proportion as they recede from tho centre . Around the perfect Avood there is seen a concentric belt of younger growth , Avhich has not yet attained to the maturity of the heart-wood . Tliis belt is called the alburnemor sap-wood ; around it is the liber or inner

barksur-, , rounded again by the outer bark . The centre of the heart-wood is occupied by the pith , ancl there is a communication betAveen the pith and the bark that is maintained b y the medullary rays , which , as their name expresses , radiate from the pith , in the C 9 ii tre of the perfect Avood , to the external coating of the wood , or bark . When cut in a sloping direction , they produce the beautifully varied appearance called " figure " in ornamental woods .

MINERAL CONSTITUENTS OF TI . AIBEK . These vary very much with the nature of the soil on which it is grown , but consist chiefly of the carbonates of potash , soda , lime , ancl magnesia , with generally a small portion of the sul phates , chlorides , ancl phosphates of the same substances . The folloAving table exhibits the Aveight of mineral ash remaining after the combustion of 1 , 0001 b . Avei ght of different Avoods , all equally dry Avhen Aveighted : —

1 , 0001 b . of elm yielded 191 b . of ash „ poplar „ 201 b . - „ „ Avillow „ 4 | lb . „ „ beech „ 21 b . to 6 lb . >¦ birch „ ,. ' . 3 | lb . „ „ oak . „ 21 b . „ „ pine „ lJlb . to 31 b . „ ash „ 51 b . to 61 b .

SAPWOOD . The sapAvood in all fir timber is useless , and very generally there is a large proportion of it in comparison to the heartAvood . It is rather a curious fact that there appears to be a difference between the pines and the generality of the hard Avood timber in this , that a small proportion of sapwood in fir is indicative of the inferiority of the timber . Thus the red pine of Scotland has fewer layers of sapAvood than either the red ine of

p Canada or of the Baltic . As a general remark , it may be stated that the greater quantity of sapwood there is about a tree of any description of fir timber , the better will be the quality of the '• ' spine , " Avhich is the technical term given to the mature wood . It should be an object Avith consumers of wood to see that their purchases include as little sapwood as possible , but it is quite impossible for deals ancl timber to be imported quite free from it .

I noticed , during the construction of Blackfriars Bridge , tAvo Avhole baulks of timber were tested as to their compressive resistance with the following results : Crippled Reduction Length . Size . with per foot . in length . Ped 20 ft I 3 in . by 13 in 118 tons or 112 tous Sin White ... „ „ 147 „ 126 „ ... | in .

CEEOSOTING TIMBER . Throughout Grimsby Docks the timber used Avas perfectly dried and creosoted by Betbell ' s process , ancl care Avas exercised to ascertain that the due amount of creosote was employed , each piece of timber being accurately Aveighed after it had undergone the creosoting process . Without for a moment doubting that chemistry may some day supply a cheap and efficient preservative against the attacks of the Avhite-ant and " rot , " still there can be no doubt Avhatever that " Betbell ' s process " is by far the most efficient yet brought to light . Thorough saturation is what is wanted , and " Betbell ' s process " can accomplish tliis .