48 BULLETIN 448, V. S. DEPARTMENT OF AGEICULTURE. 



ture divided into two portions. To one is first added a few drops of 

 alcoholic alpha-naphthol solution, then excess of sodium carbonate; 

 to the other, sodium carbonate only. With azo compounds sodium 

 formate may be substituted for the hydrazin salt. 



The reactions obtained are referred to classes as follows : 



Class A — Azo dyes. — These yield on oxidation in acid or neutral 

 solutions a diazo compound corresponding to the "first component" 

 of the dye.^ The azo group remains attached to the nonhydroxy- 

 lated or nonaminated residue, and it is noteworthy that with Chryso- 

 phenin (No. 329), the one azo color described in the table contain- 

 ing neither hydroxyl nor amino groups, the usual reaction is not 

 obtained. With dis-azo colors of the type of cotton scarlet, CgHgNs- 

 CeH4N3CioH50H(S03]S[a)2, the azo group between the two non- 

 hydroxyl-containing residues is not readily attacked, so that a diazo- 

 azo compound is formed. With dyes of class A the solution becomes 

 colorless, pale yellow, or pale orange on addition of bromin. After 

 adding the hydrazin sulphate the solution is colorless or pale brown- 

 ish or pinkish, a tendency to show a slight coloration being more 

 marked, the more nearly neutral the solution. Addition of sodium 

 carbonate alone produces no marked coloration, but alpha-naphthoi, 

 followed by the carbonate, gives a pronounced color. It is advisable 

 to add some ether to the colored mixture and shake; since if the first 

 component of the original dye was an unsulphonated amin (indi- 

 cated by "e" in the table) the new coloring matter formed will be 

 taken up by ether from the alkahne mixture, giving usually an orange 

 solution that on being poured off and treated with a large excess of 

 concentrated hydrochloric acid becomes, in most cases, violet or 

 blue. If the new dye is sulphonated (indicated by "w"), it will not 

 be extracted by the ether from the mixture. When desired, the 

 alpha-naphthol derivative, after separation by a suitable solvent, 

 may be dyed on wool or silk and further identified by the ordinary 

 spot tests with acids and alkahes. See tables for solubilities and 

 reactions of Orange I (No. 85), Fast brown N (No. 101), benzeneazo-a- 

 naphthol, and cc-naphthaleneazo-a-naphthol (serial numbers in tables : 

 55, 66, 122, 123, respectively). 



Other compounds, such as a-naphthylamin, readily couphng with 

 diazo compounds, may, of course, be used instead of the a-naphthol, 

 sodium acetate being substituted for the sodium carbonate when an 

 amin is employed. With the simple monazo colors, the reaction seems 

 almost quantitative. With benzidin dyes it takes place least smootlil}^. 



Class AA — Azo dyes, reacting like {he frecedlng class in solutions 

 tJiat contain a considerable amount of free' hydrocMoric acid, (perhaps 

 one-haK normal or above). — In neutral solutions other oxidation 



1 For action of halogens on azo compounds, see M. Schmidt, J. prakt. Chem. 84 (1912), 235. Oxidation 

 by leadperoxid, Lauth, Bui. Soc. Chim. 6 (1891) HI, 94; by nitric acid, O. Schmidt, Ber. Chem. Ges. 38 

 (1905), 3201, 4022. See also Meldola, Proc. Chem. Soc. 10 (1S94), 118, and Trans. Chem. Soc. 55 (1889), 608, 

 and 65 (1894), 841. 



