402 



BLOOD 



screw cut within the piece, upon which the saw is fixed, and which gives the ring or 

 hook of the saw sufficient stability to perform its office. Both the pulleys and saw 

 revolve together upon a truly cylindrical tube b, which is stationary, being attached by 

 a flanch c to a fixed puppet w, and on this tube as an axis the saw and pulley turn, 



and may be slid endwise by a collar 



\^. v _ , s~ ^ fitted round the centre-piece of the pulley, 



and having two iron rods (only one of 

 which can be seen at d in the figure), 

 passing through holes made through the 

 flanch and puppet B. When the saw is 

 drawn back upon its central tube, the 

 end of the latter projects beyond the 

 teeth of the saw. It is by means of this 

 fixed ring or tube within the saw, that 

 the piece of wood e is supported together 

 during the operation of sawing, being 

 pressed forcibly against it by a screw D, 

 acting through a puppet fixed to the 

 frame of the machine. At the end of 

 this screw is a cup or basin which applies 

 itself to the piece of wood, so as to form 

 a kind of vice, one side being the end of 

 the fixed tube, the other the cup at the end 



'^^ of the screw D. Within the tube A is a 



collar for supporting a central axis, which 



is perfectly cylindrical. The other end of this axis (seen at /) turns in a collar of 

 the fixed puppet E. The central axis has a pulley F, fixed on it, and giving it motion 

 by a strap similar to the other. Close to the latter pulley, a collar g is fitted on the 

 centre-piece of the pulley, so as to slip round freely, but at the same time confined 

 to move endwise with the pulley and its collar. This collar receives the ends of the 

 two iron rods d. The opposite ends of these rods are, as above mentioned, connected 

 by a similar collar with the pulley A of the saw a. By this connection, both the 

 centre-bit, which is screwed into the end of the central axis /, and the saw sliding 

 upon the fixed tube b, are brought forward to the wood at the same time, both being 

 in rapid motion, by their respective pulleys. 



10. The coaking-engine. This ingenious piece of machinery is used to cut the three 

 semicircular holes which surround the hole bored by the crown saw, so as to produce 

 a cavity in the centre of the disc. 



11. Face-turning lathe. The sheave is fixed against a flat chuck, similar to that in 

 the coaking-engine, except that the centre-pin, instead of having a nut, is tapped into 

 the flat chuck, and turned by a screw-driver. 



A complete set of this block machinery has since been made, by Messrs. Maudslay 

 and Field, for the Spanish Government, from the original drawings and models. 



Iron blocks and sheaves have been introduced with great advantage by Messrs. 

 Brown and Lenox, and are used extensively in the naval and merchant sen-ices. See 

 IEOX. 



BLOCK TIN. Metallic tin cast into a block, the weight of which is now about 

 3.J cwts. Formerly, when it was the custom to carry the blocks of tin on the backs of 

 mules, the block was regulated by what was then considered to be a load for the mule, 

 at 2% cwts. Subsequently, the block of tin was increased in size, and made as much 

 as two men could lift, or 3 cwts. It was the custom to order so many blocks of tin, 

 and the smelter, being desirous of selling as much tin as possible, continued to in- 

 crease the size of the block, so that, although 3 cwts. is the usual weight, many 

 blocks are sold weighing 3| cwts. The term is also applied to articles made of tinned 

 iron. See TIN. 



BZiOND METAL A Clayband ironstone found near Wednesbury. It is used, 

 when smelted, for making tools. 



BliOOD. (Sang, Fr. ; Blut, Ger.) The liquid which circulates in the arteries 

 and veins of animals ; bright red in the former and purple in the latter, among all 

 the groups whose temperature is considerably higher than that of the atmosphere. Its 

 specific gravity varies with the nature and health of the animal, being from 1-0527 to 

 1'0570 at 60 F. It has a saline sub-nauseous taste, and a smell peculiar to each 

 animal. It consists of a transparent, nearly colourless liquid, called the liquor san- 

 guinis, or plasma, in which vast numbers of microscopic corpuscles are suspended. 

 These corpuscles are of two kinds, some being white or colourless transparent cells, 

 whilst others, far more numerous, are of a red tint, and impart the characteristic 

 colour to the blood. The red corpuscles are present only in the blood of vertebrated 



