574 INDUSTRIAL USES OF WOOD. 



B. Dankelmann gives the following data as regards the use 

 of various woods for pit-props ; oak, greatest strength and 

 durability, but too dear ; beech stands pressure, but has low 

 transverse strength, not durable ; impregnated sprucewood 

 is better than pinewood owing to its more suitable shape ; 

 pine has greater strength and durability, but bad shape; 

 robinia is equal to oak, but dear. Vide p. 106, where the 

 latest French tests for pit-props are given. 



With the exception of beams used vertically, dovetailed 

 together in shafts, ladder-wood, and some other pieces, wood 

 for mines is required chiefly in round logs free from bark. 

 Different forms also of sawn wood are in demand for lining 

 shafts, generally in the form of inferior coniferous boards and 

 planks. Wood may be supplied in full-lengthed logs, which 

 the mining carpenter reduces to the required dimensions; or in 

 the form of pit-props, in which the chief bulk of mining timber 

 is comprised, and which vary from three to eight inches in 

 mid-diameter (not less than 2J inches at the smaller end), and 

 12 to 30 feet long, and even longer. Only about 15 to 20 per 

 cent, of the mining-props are required in pieces measuring 12 

 to 16 inches, mid-diameter. 



[Scots pine will yield pit-props when 40 years old, and birch 

 at 25 years, and for British coal-mines over 600,000 tons of 

 Cluster pine are imported annually from Bordeaux, where 

 this tree is grown and tapped for resin in the extensive forests 

 of the Landes and Gironde. This gives about 1 ton of wood 

 for 30 tons of coal, the wood costing about 15/- a ton. Tr.] 



Wood is put to some other uses where it is subject to similar 

 conditions as wood used in mines ; for instance, well-frames, 

 for which purpose resinous coniferous wood, especially that of 

 larch, black pine, and Scots pine are suitable ; also in cellars, 

 for bottle-racks, for which oakwood, good pinewood (or iron) 

 are chiefly used. 



SECTION IV. WOOD USED IN CONTACT WITH WATER. 



1. Bridges, etc. 



Wood used in watercourses and bridges is under very much 

 the same circumstances as wood in contact with the ground, 



