Milling Yellow 3G

Property Data
Common name
Suggested name
Other names
C.I. number
C.I. name
Class
Ionisation
Solubility aqueous
Solubility ethanol
Absorption maximum
Colour
Empirical formula
Formula weight
Milling yellow 3G
Acid yellow 40
Numerous others
18950
Acid yellow 40
Azo
Acid
3%
4%
412
Yellow
C23H18ClN4NaO7S2
584.99

A dye named milling yellow 3G was specified in Slidders’ fuchsin-miller technique for fibrin. It is not possible to identify the dye with certainty as there are three dyes with that name recorded in the second edition of the Colour Index. Those dyes are acid yellow 40 (CI 18950), acid yellow 42 (CI 22910) and acid yellow 56 (CI 24825).

The commercial name milling yellow 3G was listed as a designation for acid yellow 40. However, it was noted in the addendum for additions and alterations that the name milling yellow 3G was to be removed as a designation for acid yellow 56. It was also noted that it was to be added to the list of names for acid yellow 42.

To complicate the issue, Gurr lists milling yellow 3G but gives the formula for acid yellow 56, despite the Colour Index specifying that the commercial designation of milling yellow 3G should not be applied to that dye (it should be milling yellow H3G).

To complicate it even further, the commercial name milling yellow is applied to a large number of other dyes. Milling is a dyeing process for wool and yellow is a popular colour, so it is not surprising. The letter designations following the name vary considerably for different dyes, but occasionally dye manufacturers coincidentally use the same designation. This is perhaps a case where the CI name should have been used.

So, which dye is the one meant? The most likely choice is acid yellow 40. This is noted to be soluble in both water and cellosolve (2-ethoxethanol), the common solvent used in techniques similar to the fuchsin miller. It is also very similar in structure to tartrazine, another dye which is commonly used for a similar purpose in a technique from which the fuchsin-miller is derived. The formula and data above are for acid yellow 40. Information about the other dyes is below.

The other dyes

Acid yellow 42, CI 22910

Property Data
Common name
Suggested name
Other names
 
C.I. number
C.I. name
Class
Ionisation
Solubility aqueous
Solubility ethanol
Absorption maximum
Colour
Empirical formula
Formula weight
Milling yellow 3J
Acid yellow 42
Sulphon yellow R
Numerous others
22910
Acid yellow 42
Azo
Acid
3%
Less than 0.1%
410
Yellow
C32H24N8Na2O8S2
758.69

Acid yellow 56, CI 24825

Property Data
Common name
Suggested name
Other names
C.I. number
C.I. name
Class
Ionisation
Solubility aqueous
Solubility ethanol
Absorption maximum
Colour
Empirical formula
Formula weight
Milling yellow H3G
Acid yellow 56
Airedale yellow 3GM
24825
Acid yellow 56
Azo
Acid
Moderate
Moderate
391 (Gurr)
Greenish yellow
C41H32N8O8S2Cl2Na2
946

 

Reference
Edward Gurr, (1971)
Synthetic dyes in biology, medicine and chemistry
Academic Press, London, England.

Colour Index, Ed. 2. (1956)
Society of dyers and colourists, UK.

Green, F (1990)
The Sigma-Aldrich handbook of stains, dyes and indicators
Aldrich Chemical Company, Milwaukee, Wisconsin, USA

 


 

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