COL 



COL 



ers 

 ole 



with the point of a needle, after which 

 the papers thus marked were put away, 

 and afresh paper substituted for other ex- 

 periments, the measurement or compari- 

 son of the lengths of the intervals occu- 

 pied byeach colour on the different pap 

 being purposely deferred, until the wh 

 course of experiments was completed, in 

 order to prevent any preconceived opi- 

 nions from operating, in making the ex- 

 periments : the results are represented 

 as agreeing, in the spaces, , T ^, _!_, 



T5> TT TfV and TV c c "P ied b y ^e vio- 

 let, indigo, blue, green, yellow, orange, 

 and red colours, being the very same, as 

 to arrangement, as those by refraction 

 above mentioned. 



COLOUR of office, signifies some unjust 

 action, done under countenance of an of- 

 fice, and is opposed to virtute ojfficii, which 

 implies a man's doing a right and just 

 thing in the execution of his office. 



COLOURS, in the military art, include 

 the banners, flags, ensigns, &c. of all 

 kinds, borne in the army or fleet. See 

 ENSIGN, FLAG, PENDANT, and STANDARD. 



COLOURING, in painting, one of the 

 great component and essential parts of 

 painting, is the art of giving to every ob- 

 ject in a picture its true and proper hue, 

 as it appears under all the various circum- 

 stances or combinations of light, middle- 

 tint, and shadow ; and of so blending and 

 contrasting the colours, as to make each 

 appear with the greatest advantage and 

 beauty, at the same time that it contri- 

 butes to the richness, the brilliancy, and 

 the harmony of the whole. It likewise 

 possesses powers, which, when judicious- 

 ly applied, render it highly conducive to 

 the character and expression of the sub- 

 ject represented. See PAINTING. 



COLOURING matter. It has been sup- 

 posed that a peculiar proximate princi- 

 ple exists in vegetables, in which their 

 colour frequently resides, and which has 

 hence received the name of colouring 

 matter. 



The colouring matter of vegetables is 

 scarcely ever found insulated, but is mix- 

 ed or combined with other principles. In 

 this state it exists in the leaves and 

 flowers, in the bark, and in the wood of 

 the stem and roots. It is extracted, and 

 obtained more pure, by the action of those 

 agents which are capable of dissolving it. 

 In many cases, water, cold or warm, is 

 sufficient for this purpose. If logwood, 

 brazil wood, madder, weld, or querci- 

 tron bark, for example, be macerated in 

 water, the matter on which the colour 

 depends is dissolved ; a transparent solu- 



tion, more or less deeply coloured, is ob- 

 tained ; and, by repeating the macera- 

 tion with water sufficiently, nothing at 

 length remains but the mere ligneous fi- 

 bre. Sometimes, however, the colour- 

 ing matter is not soluble in water : it is 

 then frequently soluble in alcohol ; and, 

 in a few substances, is even best dissolved 

 by oils essential or expressed. 



When the colouring matter is in solu- 

 tion, it may be attracted from the solvent 

 by other substances with which it enters 

 into combination : and this, in some mea- 

 sure, gives it a more appropriate charac- 

 ter. There are some substances even 

 which appear in general to exert strong 

 affinities to colouring matter, particular- 

 ly alumina and some of the metallic ox- 

 ides. If alumina be diffused or boiled in 

 a coloured vegetable infusion, it often 

 happens, that the colouring matter com- 

 bines with it, and leaves the water of the 

 infusion perfectly colourless. Or if alum 

 be dissolved in a coloured infusion, and it 

 be decomposed by the addition of an al- 

 kali, the alumina, in the moment of its 

 precipitation, attracts the colouring mat- 

 ter, forms a coloured precipitate, and, if 

 the due proportions have been observed, 

 the liquid w ill remain colourless. In like 

 manner, if a coloured infusion be boiled 

 with a metallic oxide, it often happens, 

 that the colouring matter is attracted by 

 the oxide. Thus Berthollet obtained 

 combinations by this process of the co- 

 louring matter of logwood, and other dye- 

 stuffs, with oxide of copper, and oxide of 

 tin. Or if certain metallic salts be dis- 

 solved in the infusion, and be then de- 

 composed by an alkali, the oxide, in pre- 

 cipitating, equally attracts the colouring 

 matter. It is from similar affinities to the 

 colouring matter that it is often attracted 

 by linen, cotton, silk,' or wool, from its 

 solutions ; and even where the affinities 

 of these are not sufficiently powerful, 

 they may be rendered capable of attract- 

 ing it, or the combination may be render- 

 ed more permanent by their being im- 

 pregnated with another substance, which 

 has towards it a still stronger attraction. 

 See DYEING. 



COLPODA, in natural history, a genus 

 of the Vermes Infusoria : worm, invisible 

 to the naked eye, very simple, pellucid, 

 flat sinuate. There are seven species, of 

 which C. lamella, in water, resembles a 

 long, narrow, pellucid membrane, narrow- 

 er and obtuse behind, curved towards 

 the top, with aridge orfold going through 

 the middle : it moves to and fro on its 

 edge, and not so on the flat side. 



