2,4-dinitrophenyl hydrazine test I found this reaction over here:  

   

which illustrates the carbonyl test but looks fuzzy.  

Assuming that the R in the product is a typo for H, I couldn't conserve the number of Nitrogen atoms.  

What is the correct reaction?
Is this correct?
Is there a possibility of a methyl substitution on the ring in a variant of this test?
Somebody messed up the scheme completely!

As you have already imagined, there is no magical $\ce{NO2}$ to $\ce{CH3}$ conversion in this classical reaction ;-)



In the times before modern spectroscopy, these reactions were valuable analytical tools: the melting points of the dinitrophenylhydrazones and/or other derivatives were used to identify the carbonyl compounds.