CAO 



CAP 



its properties. From experiments he con- 

 cluded, that caoutchouc exists ready form- 

 ed in the juice of the tree, and is capable 

 of being separated in the concrete form ; 

 but that a portion also exists, not suffici- 

 ently perfect to be deposited with its 

 elastic property ; that it acquires this, to- 

 gether with its inspissation, from the ac- 

 tion of oxygen; and that, by this opera- 

 tion, exposure to the atmosphere influ- 

 ences the concretion of caoutchouc in the 

 usual process in which it is brought to 

 the solid form. 



The purest caoutchouc Fourcroy sup- 

 poses to be that which separates sponta- 

 neously from the juice in close vessels. It 

 is white, or of a slight fawn colour. The 

 properties of caoutchouc have been de- 

 termined, principally, from the state in 

 which it exists in the elastic bottles which 

 are imported to Europe ; and in this state 

 its properties do not seem to have under- 

 gone any important change, or to be dif- 

 ferent from those of the pure caoutchouc. 

 Its colour is a dark brown ; its external 

 surface is smooth ; its internal texture 

 is rough, and presents a fibrous appear- 

 ance. Its specific gravity is nearly the 

 same with water, being from 9.3 to 10.0. 

 It is inodorous, and is also destitute of 

 taste. 



The most remarkable physical property 

 of which this substance is possessed, and 

 which eminently distinguishes it, is its 

 high elasticity. It can be stretched out 

 to a great length, and when the force 

 that has been applied to it is withdrawn, 

 it instantly returns to its former dimen- 

 sions. Its pliancy is increased by heat, 

 while it is rendered more rigid by cold ; 

 and its softness, which is connected with 

 the former quality, is so much increased 

 by warmth, that it can be moulded into 

 any form, and two parts newly cut may 

 even be pressed together, so as to be in- 

 timately united. 



Caoutchouc, exposed in a dry state to 

 a high temperature, softens, swells up, 

 and emits a fetid odour, similar to that of 

 animal' substances : as the heat is in- 

 creased, it melts into a viscid matter, and 

 remains in this state when cold. If heated 

 sufficiently high, it takes fire, and burns 

 with a vivid light and dense smoke ; in 

 the countries in which it is produced it 

 has been used for torches. It is perfectly 

 insoluble in water and alcohol, but is dis- 

 solved in either. 



This substance is capable of being ap- 

 plied to important purposes, from its 

 softness and flexibility, its elasticity, and 



particularly its indestructibility, and not 

 being affected by air, water, or indeed 

 the' greater number of chemical agents. 

 Tubes for conveying gases, and other 

 chemical instruments, are accordingly 

 prepared from it ; and bougies, catheters, 

 and similar surgical instruments of ca- 

 outchouc, are much preferable to what 

 can be prepared from any other sub- 

 stance. 



The solution of caoutchouc in some of 

 the oils has been used as a varnish, to 

 render flexible substances, as silk, &c. 

 impermeable to water or air. It has the 

 advantage of being perfectly flexible; but 

 it is long before it dries, and is liable to 

 be softened by a very moderate heat. 

 To render it less viscid, it is generally 

 prepared from a mixture of volatile and 

 expressed oils. 



CAP of maintenance, one of the rega- 

 lia, or ornaments of state, belonging to 

 the kings of England, before whom it was 

 carried at the coronation, and other great 

 solemnities. Caps of maintenance are also 

 carried before the mayors of several cities 

 in England. 



It is of crimson velvet, faced with er- 

 mine, and was formerly esteemed a badge 

 and symbol of dignity, and suitable to a 

 prince of the blood, being worn by King 

 Edward III. and succeeding sovereigns 

 down to Edward VI. but of late it has 

 been granted to private families. It is 

 frequently to be met with above the hel- 

 met, instead of a wreath, under gentle- 

 men's crests. 



CAP, in a ship, a square piece of tim- 

 ber put over the head or upper end of 

 any mast, having a round hole to receive 

 the mast. By means of these caps the 

 top-masts and top -gall ant-masts are kept 

 steady and firm in the tressel-trees where 

 their feet stand. 



CAP of a gun, a piece of lead which is 

 put over a touch-hole of a gun, to keep 

 the priming from being wasted or spoiled. 



CAPACITY, in a general sense, an ap- 

 titude or disposition to retain or hold any 

 thing. 



CAPACITY, in geometry, is the solid 

 contents of any body ; also our hollow 

 measures for wine, beer, corn, salt, &c 

 are called measures of capacity. 



CAPACITY, in the modern doctrine of 

 heat, signifies the proportional capabi- 

 lity of a given quantity of any substance 

 to absorb and retain caloric, or that dis- 

 position or property, by which various 

 bodies respectively require more or less 

 of this fluid to superinduce any given 



