Artificial organic colouring matters

Eosin is detected by treating the carmine with dilute sulphuric acid, shaking with ether and evaporating the ethereal solution the eosin may then be identified in the residue. 

Biebrich s scarlet is recognised by boiling the substance with ammonia in presence of this colouring matter the liquid assumes an orange-red tint, whilst with pure carmine a purple-red liquid is obtained. 

The ash of genuine carmine usually varies from 5 to 9% and consists mainly of alumina and lime, with small proportions of magnesia, alkalies and phosphoric acid often, however, it contains traces of copper and tin oxides derived from the vessels used in its preparation. 

The colouring matter is contained in carmine to the extent of 30-65%, but more commonly 45-56%. 

These (commonly termed coal-tar colours) are classified, according to their chemical constitution and to the atomic groupings characteristic of each colouring matter, into various groups, the principal ones being  

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Extraneous Organic Colouring Matters.—Tests are made especially for artificial organic colouring matters by the methods indicated for liqueurs and wines (q.v.). 

If, however, the coloration is feeble or uncertain, the woollen thread is treated with 50 c.c. of water and 10 drops of ammonia (D 0-910), the colour being refixed, by the exact procedure described above, on a fresh woollen thread 6-8 cm. long. If this third fixation yields even a feeble pink coloration, the presence of artificial organic colouring matter is indicated with certainty. 

If the wine is genuine, the ether remains colourless even after addition of acetic acid coloration of the ether before or after acidification indicates the. presence in the wine of artificial organic colouring matters of basic character (fuchsine, etc.). 

Cognac may also be coloured by addition of other substances, especially caramel or artificial organic colouring matters. 

To ascertain if the cognac is coloured with artificial organic colouring matters, the alcohol is evaporated off, ammonia solution added and the liquid extracted with amyl alcohol evaporation of the amyl alcohol gives the colouring matters, which may be detected by their characteristic reactions and by dyeing tests with wool in acid or alkaline solution (see also Wine, and Colouring Matters). 

The coloured materials most frequently added are gamboge, dragon s blood, turmeric, indigo, and especially artificial organic colouring matters. For some varnishes mineral colours are used, such as ferric oxide, white lead, minium, lamp black, etc. 

Some artificial organic colouring matters, in the form of lakes, may be insoluble, in the. above, solvents in such cases they are identified after decomposition of the lake with alkali or acid. 

The qualitative examination is completed by testing for artificial organic colouring matters by treatment in the hot with alcohol, either alone or in presence of acetic acid or ammonia (see also General Methods, p. 371). 

The artificial organic colouring matters form the large class known as coal-tar dyes. 

Artificial organic colouring matters may be in powder, crystals, lumps or more or less aqueous paste. They exhibit various tints often different from those they impart to the fibre they frequently show iridescence and metallic lustre, especially if crystallised. 

Analysis of an artificial organic colouring matter may be required for various purposes (i) to determine its nature (2) to ascertain the purity and any adulteration (3) to determine its value as regards tintorial properties. 

Of the extraneous substances which may be found n artificial organic colouring matters (besides water, especially in pasty materials), some may be derived from the manufacture, such as sodium chloride and sulphate others, such as zinc and ferric chlorides, may form integral parts of certain colours, which are prepared as double salts with these chlorides others may consist of mordants mixed with the colouring matter, such as aluminium, iron, chromium, antimony and copper salts, cream of tartar, tannin, etc. 

For the Identification of Artificial Organic Colouring Matters on Cotton... 

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