308 



BLOCK MANUFACTURE 



a general constituent of blende. The cadmiferous varieties are termed Przibramite. 

 The blende from the King William mine at Clausthal contains, according to Kuhle- 

 mann, 0'63 per cent, of antimony, 0'79 of cadmium, and 0-13 of copper, besides 1'18 

 of iron. Blende is met with in association with galena, iron-pyrites and copper-py- 

 rites, from which it should be dressed as clean as possible, although in this there is 

 some difficulty, owing to the very close approximation of the specific gravities of those 

 ores. Blende is occasionally argentiferous, and sometimes sufficiently so to allow of 

 the profitable extraction of the silver. In one of the mines in the Chivorton district, 

 near Truro, Cornwall, some very fine examples of this argentiferous blende have been 

 discovered. In one of the zinc ores of Silesia, the new metal INDIUM has been dis- 

 covered by the aid of spectrum analysis. Plattner states that blende occasionally 

 contains traces of tin and manganese. (Percy's Metallurgy.') The red varieties of 

 blende often contain from 2 to 3 per cent, of sulphide of cadmium, especially that 

 which is found at Marmato, near Popayan. Dana has quoted the following analyses of 

 varieties of blende : 



See INDIUM ; HAEMATITE. 



BLEU DE LYONS. 



BLEU 1>B PARIS. See ANILINE-BLUE. 



BIiICHT. A disease in plants frequently produced by atmospheric, or by physical 

 agencies. A peculiar blight has been referred to the action of the extra-spectral heat 

 rays. Blight is sometimes of insect origin, but more frequently it arises from parasitic 

 fungi. See PAEATHEBMIC KAYS and FUNGI. 



BLIND CO All, a name given to anthracite in some parts of Scotland. See AN- 



THBACITE. 



BLISTER COPPER-ORE. A botryoidal variety of copper-pyrites, which 

 has been found at the copper mines in the neighbourhood of Camborne, in remark- 

 ably fine masses. Of late years it has been but rarely found in those mines. See 

 COPPER. 



BLISTER-STEEL. Bars of steel which exhibit blister-like protuberances. 

 See STEEL. 



BLOCK MAITOFACTTTKE. Though the making of ships' blocks belongs 

 rather to a dictionary of engineering than of manufactures, it may be expected that 

 some account should be given of the automatic machinery for making blocks, so ad- 

 mirably devised and mounted by Sir M. I. Brunei, for the British Navy, in the dock- 

 yard of Portsmouth. 



The series of machines and operations are as follows : 



1. The straight cross-cutting saw. The log is placed horizontally on a very low 

 bench, which is continued through the window of the mill into the yard. The saw 

 is exactly over the place where the log is to be divided. It. is lot down, and suffered 

 to rest with its teeth upon the log, the back still being in the cleft of the guide. The 

 crank being set in motion, the saw reciprocates backwards and forwards with exactly 

 the same motion as if worked by a carpenter, and quickly cuts through the tree. 

 When it first begins to cut, its back is in the cleft in the guide, and this causes it to 

 move in a straight line ; but before it gets out of the guide, it is so deep in the wood 

 as to guide itself ; for, in cutting across the grain of the wood, it has no tendency to be 

 diverted from its true line by the irregular grain. When the saw has descended 

 through the tree, its handle is caught in a fixed stop, to prevent its cutting the bench. 

 The machine is thrown out of gear, the attendant lifts up the saw by a rope, removes 

 the block cut off, and advances the tree to receive a fresh cut. 



2. The circular cross-cutting saw. This saw possesses universal motion ; but the 

 axis is always parallel to itself, and the saw in the same plane. It can be readily 

 raised or lowered, by inclining the upper frame on its axis ; and to move it sidewise, 

 the saw-frame must swing sidewise on its joints which connect it with the upper frame. 

 These movements are effected by two winches, each furnished with a pair of equal 

 pinion*, working a pair of racks fixed upon two long poles. The spindles of those 

 winches-%re fixed in two vertical posts, which support the axis of the upper frame. 

 One of these pairs of poles is jointed to the extreme end of the upper frame ; there- 

 fore, by turning the handle belonging to them, the frame and saw are elevated or do- 



