BLO 



BLO 



BLOCKS, on ship-board, is the usual 

 name for what we call pullies at land. 

 They are thick pieces of wood, some 

 with three, four, or five shivers in them, 

 through which all the running 1 ropes run. 

 Blocks, whether single or double, are 

 distinguished and called by the names of 

 the ropes they carry, and* the uses they 

 .serve for. 



Double blocks are used when there is 

 occasion for much strength, because they 

 will purchase with more ease than single 

 blocks, though much slower. 



Block and block, is a phrase signifying 

 that two blocks meet, in haling any tackle 

 or halliard, having such blocks belonging 

 to them. 



The blocks now used in the navy are 

 made in Portsmouth by means of circular 

 saws and other machinery, which have 

 been lately erected by a most ingenious 

 mechanician. This machinery performs 

 the several operations, from the rough 

 timber to the perfect block, in the com- 

 pletest manner possible. The whole is 

 worked by means of a steam-engine ; the 

 manual labour required is simply to sup- 

 ply the wood as it is wanted to the seve- 

 ral parts of the machinery, so that the 

 commonest labourer almost may be made 

 to act in this business with very little in- 

 struction. 



Fish block is hung in a notch at the end 

 of the davit ; it serves to hale up the 

 flooks of the anchor at the ship's bow. 



Snatch block is a great block with a 

 shiver in it, and a notch cut through one 

 of its cheeks, for the more ready receiving 

 of any rope ; as by this notch the middle 

 part of a rope may be reeved into the 

 block without passing it endwise. It is 

 commonly fastened with a strap about 

 the main mast close to the upper deck, 

 and is chiefly used for the fall of the 

 winding tackle, which is reeved into this 

 block, and then brought to the capstan. 



BLOCK house, a kind of wooden fort or 

 battery, either mounted on rollers, or on 

 a vessel, and serving either on the water 

 or in counterscarps and counter approach- 

 es. The name is sometimes also given 

 to a brick or stone fort built on a bridge, 

 or the brink of a river, serving not only 

 for its defence, but for the command of 

 the river both above and below ; such was 

 that noted block-house anciently on the 

 bridge of Dresden, since demolished on 

 enlarging the bridgs. 



BLOCKADE, in the art of war, the 

 blocking up a place by posting troops at 

 all the avenues leading to it, to keep sup- 

 plies of menaadprgv>siQns from 



YOJt. Iv. 



into it ; and by these means proposing to 

 starve it out without making any regular 

 attacks. 



To raise a blockade, is to force the 

 troops that keep the place blocked up 

 from their posts. 



BLOOD is a well known fluid, which 

 circulates in the veins and arteries of the 

 more perfect animals. It is of a red co- 

 lour, has a considerable degree of consis- 

 tency, and an unctuous feel, as if it con- 

 tained a quantity of soap. Its taste is 

 slightly saline, and it has a peculiar smell. 

 The specific gravity of human blood is, 

 at a medium, 1.05. Mr. Fourcroy found 

 the specific gravity of bullock's blood, at 

 the temperature of 60, to be 1.056. The 

 blood, does not uniformly retain the same 

 consistence in the same animal, and its 

 consistence in different animals is very 

 various. It is easy to see that its specific 

 gravity must be equally various. When 

 blood, after being drawn from an animal, 

 is allowed to remain for some time at rest, 

 it very soon coagulates into a solid mass, 

 of the consistence of curdled milk. This 

 mass gradually separates into two parts, 

 one of which is fluid, and is called serum ; 

 the other, the coagulum, has been called 

 cruor, because it alone retains the red co- 

 lour which distinguishes blood. This se- 

 paration is very similar to the separation 

 of curdled milk into curds and whey. 

 The proportion between the cruor and 

 serum of the blood varies much in different 

 animals, and even in the same animal in 

 different circumstances. The most com- 

 mon proportion is about one part of 

 cruor to three parts of serum. 1. The 

 serum is of a light greenish yellow colour: 

 it has the taste, smell, and feel of the 

 blood, but its consistence is not so great. 

 It converts syrup of violets to a green, 

 and therefore contains an alkali. On ex- 

 amination, Roulle found that it owes this 

 property to a portion of soda. When, 

 heated to the temperature of 156, the 

 serum coagulates. It coagulates also 

 when boiling water is mixed with it, but if 

 serum be mixed with six parts of cold 

 water, it does not coagulate by heat. 

 W T hen coagulated, it has a greenish white 

 colour, and is not unlike the boiled white 

 of an egg. If the coagulum be cut into 

 small pieces, amuddy fluid may be squeez- 

 ed from it, which has been termed the 

 serosity. After the separation of this fluid, 

 if the residuum be carefully washed in 

 boiling water and examined, it will be 

 found to possess all the properties of co- 

 agulated albumen. The serum, therefore, 

 contains a considerable proportion of al 





