TRANSACTIONS OF SECTION B. 643 



blue colour, wliicli upon gradual dilution Avith water slowly changes to a red, the 

 colouring matter being reprecipitated in red Hakes by excess of water. Although 

 insoluble in water it is slightly soluble in dilute sulphuric and also in acetic acid, 

 and silk may be dyed a fine crimson shade in baths acidified with these acids. If 

 the colouring matter is dissolved in strong sulphuric acid and a single drop of con- 

 centrated nitric added to the solution the colour immediately changes from a dark 

 blue to a claret shade. The latter reaction and the behaviour of the sulphuric 

 acid solution upon diluting with water are two equally characteristic and delicate 

 tests. 



The action of alkaline-reducing agents, viz., of sodium ethylate and methylate, 

 sodium amalgam and ammonium sulphide in alcoholic solution upon tetra-nitro-a- 

 pyrocresol oxide, gives rise to the formation of varying quantities of amido- and of 

 azo-compounds. The action of ammonium sulphide is particularly interesting. 

 If a small quantity of the nitro-compound is heated with alcohol and a few drops 

 of ammonium sulphide, the supernatant liquid assumes a reddi.sh-brown colour, 

 and upon the addition of hydrochloric acid and warming a red precipitate is 

 formed, insoluble in water, but soluble in chloroform, alcohol, ether, benzene, and 

 acetone with a reddish-violet colour. It is practically insoluble in carbon disul- 

 phide, and thus may be separated from any admixture of sulphur. With strong 

 sulphuric acid it yields a yellowish solution, and upon diluting the colourino- 

 matter separates unchanged as a red precipitate. It dyes silk a reddish shade, but 

 only in strongly acid baths. 



By protracted treatment of the nitro-compound with excess of alcoholic 

 ammonium sulphide a solution is obtained which with hj-drochloric acid no loncer 

 yields a red colour. On adding water a yellow precipitate is formed, insoluble in 

 hydrochloric acid, slightly soluble in cold water, and a little more soluble in hot 

 water, the hot aqueous solution dyeing silk a fine yellow. The colouring matter 

 is only slightly soluble in alcohol, ether, chloroform, and almost insoluble in benzene. 



We have not had sufficient time to determine the composition of the red and 

 _yellow colourmg matters which have only quite recently been prepared. From 

 their mode of formation it would appear that the red body is an azoxy- or else 

 oxyazo-derivative, whilst the yellow substance would be azo-pyrocresol oxide ; 

 still this is a mere conjecture, and their composition may turn out to be of a more 

 complex nature. 



It is proposed to apply the above reactions to the /3- and y-isomerides of pyro- 

 cresol, and, by sulphonating or otherwise, to prepare the colouring matters in a 

 pure and soluble condition, and to study their special qualities as dyes. Experi- 

 ments are also in progress to obtain direct nitro-substitution products of the 

 pyrocresols, of which only the nitrated oxides are known, and to prepare the 

 phenols corresponding to the sulphonic acids. 



Of nitrated derivatives of the pyrocresols only the tetra-nitro-compounds of 

 the respective oxides had been obtained, no intermediate product being known. 

 A dinitro-a-pyrocresol oxide, C,jH,o(NO,)20o, has, however, been lately prepared 

 by treating a-pyrocresol oxide with cold concentrated nitric acid and extracting 

 the product with boiling alcohol to remove unaltered oxide. It forms yellowish- 

 white crystals melting at about 235°. 



The main work being still progressing, little can be added to the views 

 expressed in the pre\dous paper on the structure of the pyrocresols. The funda- 

 mental question as to the position of the oxygen atom in the molecule of pyro- 

 cresol, C,-Hi^O, thus still remains open. An argument in favour of the existence 

 of the carbonyl group in the molecule of a-pyrocresol at least might be found in 

 the formation of the reduction product O,.!!.,"., ; but we have formerly stated our 

 reasoiis against this supposition, tstill adhering to the belief that a-pyrocresol 

 contains the oxygen atom linked to two carbon atoms, the production of the 

 compound C,jri„., necessitates the assumption of a closed ring instead of two 

 separate chains ; thus : 



CrlLrO. 



I >o. 



CyllyC/ 



