COLOUR 893 



Journal of Medical Science, but they failed in procuring the cotton in a state in which 

 it could be dissolved in ether. It appears that these experimentalists had employed a 

 mixture of nitric and sulphuric acids ; but M. Miallie ascertained, after many trials, 

 that the collodion in a state fitted for solution was much more easily procured by 

 using a mixture of nitrate of potash and sulphuric acid. 



For the information of our readers, we give here a description of M. Miallie's 

 process for its preparation. It appears from the results obtained from this chemist, 

 that cotton in its most explosive form is not the best fitted for making the ethereal 

 solution : 



Parts by weight 



Finely-powdered nitrate of potash . . .40 



Concentrated sulphuric acid . . . .60 



Carded cotton . . . . .2 



Mix the nitrate with the sulphuric acid in a porcelain vessel, then add the cotton, and 

 agitate the mass for three minutes by the aid of two glass rods. Wash the cotton, with- 

 out first pressing it, in a large quantity of water, and when all acidity is removed 

 (indicated by litmus paper), press it firmly in a cloth. Pull it out into a loose mass, 

 and dry it in a stove at a moderate heat. 



The compound thus obtained is not pure fulminating cotton ; it always retains a 

 small quantity of sulphuric acid, is less inflammable than gun-cotton, and it leaves a 

 carbonaceous residue after explosion. It has, however, in a remarkable degree the 

 property of solubility in ether, especially when mixed with a little alcohol, and it forms 

 therewith a very adhesive solution, to which the name of collodion has been applied. 



Preparation of Collodion, Prepared cotton, 8 parts; rectified sulphuric ether, 125 

 parts ; rectified alcohol, 8 parts : all by weight. 



Put the cotton with the ether into a well-stopped bottle, and shake the mixture for 

 some minutes. Then add the alcohol by degrees, and continue to shake until the whole 

 of the liquid acquires a syrupy consistency. It may be then passed through a cloth, 

 the residue strongly pressed, and the liquid kept in a well-secured bottle. 



Collodion thus prepared possesses remarkable adhesive properties. A piece of linen 

 or cotton cloth covered with it, and made to adhere by evaporation to the palm of the 

 hand, will support a weight of twenty or thirty pounds. Its adhesive power is so great 

 that the cloth will commonly be torn before it gives way. The collodion cannot be 

 regarded as a perfect solution of the cotton. It contains suspended and floating in it 

 a quantity of vegetable fibre, which has escaped the solvent action of the ether. The 

 liquid portion may be separated from these fibres by a filter, but it is doubtful whether 

 this is an advantage. In the evaporation of the liquid these undissolved fibres, by 

 felting with each other, appear to give a greater degree of tenacity and resistance "to 

 the dried mass. 



Small balloons for holding gas are also made of collodion by pouring it into a 

 glass globe, and turning it about, so that every part is covered with the fluid. As 

 the ether evaporates, a thin film is left on the surface of the glass. To remove this, 

 a glass tube is inserted into the neck of the flask, so that the collodion film may 

 adhere ; the air is sucked out, and the collapsed film is easily withdrawn. 



For the application of collodion to photography, see PHOTOGRAPHY. 



COLOCYNTH. Citrullus Colocynthis. The Coloquintida, bitter cucumber or 

 bitter apple, a drastic medicine. 



COLOGNE EARTH. A brown pigment, prepared from lignite or brown coal. 



COLOGNE YELLOW. This pigment consists of a mixture of chromate and 

 sulphate of lead with sulphate of lime. It is prepared by precipitating a mixture of 

 nitrate of lead and nitrate of lime, with sulphate of soda and chromate of potash. 



COIiOXVXBA. Cocculus palmatus. A climbing shrub, a native of the intertropical 

 regions of the earth. It is now cultivated in the Mauritius and the Isle of Bourbon. 

 The root is of a large, fleshy, deep yellow colour, and divided into many irregular 

 forks. These are cut off, sliced, strung on cords, and hung to dry in the shade. 



COLOPHONY. Black resin, the solid residuum of the distillation of turpentine 

 when all the oil has been worked off. 



COLORINE. An alcoholic extract of garancine, when evaporated, is known in 

 commerce as colorine. It contains the colouring principles of madder (alizarine and 

 purpurine), together with fatty matter and other components of the garancine, which 

 are capable of extraction by alcohol. 



COLOUR. In Physics, a property of light, producing peculiar impressions 

 through the eye. Every surface, differing in its mechanical structure or chemical 

 character, acts differently towards the light falling on it, and according to the amount 

 of absorption, or reflection, or refraction, so is the colour of the ray. White is an 

 entire reflection, and black & total absorption of all the rays, and consequently are 

 not colours. The following Table is by Mr. William Linton : > 



