410 Prof. Baphaei Meldola on the 



difficulty of forming diazo-salts. When once diazotized this 

 and analogous orthoamidoazo-compounds form tetrazo-salts, 

 which differ in so many ways from the corresponding com- 

 pounds of the para- or a-series that Zincke has suggested* the 

 closed chain formula : — 



.N— N .X' N : N . X' 



X"(| | instead of X"( 



N-N.C1 N:N.C1 



It would be out of place here to discuss the evidence in 

 favour of this formula, and I have only to express my con- 

 currence therewith. 



The relationship of orthoamidoazo-compounds to the 

 azimides is shown at once by the formula now proposed. The 

 oxidizing agent simply removes the two H-atoms : — 



/ N \ N 



IT- X H ^ 



These oxidized products are very stable and are not acted 

 upon by reducing-agents, a fact also expressed by the formula. 

 With reference to the azimides, theory indicates the existence 

 of two isomeric series derived from 



x"T I ;nh and x"/ x ;n 



X W X NIT 



The first of these formulas was proposed by Griess for his 

 azimido-compounds, and the second by Kekule and Laden- 

 burg for the same compounds. I have already given evidence 

 to the effect that the latter is probably the correct formula f, a 

 conclusion which has since been confirmed by Nolting and 

 Abt J. It follows, therefore, that Zincke's oxidized products 

 are not true azimido-compounds, but belong to the isomeric 

 series. If the said products were constructed on Kekule's 

 type, the orthoamidoazo-compounds would have the formula: — 



X< >H 

 H 



* Ber. 1886, p. 1452. 



t Phil. Mag. 1887, vol. xxiii. p. 525. % Ber. 1887, p. 2999. 



