1896.] G. S. A. Ranking — A Note on Indigo Manufacture. 53 



probably one of the so-called " Indigo-browns " of which as I shall 

 shew there appear to be at least two. 



This Sodium-silver-indigo compound is like the potassium-silver- 

 indigo compound in appearance, but is browner, and does not detonate 

 when heated, nor does it yield a sublimate of Indigo-blue. It is insolu- 

 ble in water, alcohol, or ether, partially soluble in dilute nitric acid with 

 decomposition of the acid. Partially soluble in NH 4 HO dilute, with 

 which it forms a dark brown solution leaving a black residue in powder ; 

 less easily soluble in Na OH or KOH to brown solution. Sodium 

 chloride gives no precipitate. The ammoniacal solution is brown by 

 reflected light, deep vinous red by transmitted light, it passes through 

 filter paper unchanged (A), leaving a fine black powder on the filter (B). 



(1) A. Filtrate of NH 4 HO solution. Added HC1 in excess, no 

 ppt. With HN0 3 dil. decolorized on boiling, and gives with HC1 a white 

 ppt. sol. in NH 4 HO ; HN"0 3 driven off by evaporating to dryness, con- 

 firmed with K 2 Cr0 4 . 



(2 ) Portion of filtrate evaporated to dryness over a water bath 

 was greenish black with metallic lustre, when heated gave a faint 

 brown sublimate not yielding Indigo-blue on treatment with H 2 S0 4 

 cone, and subsequent addition of water. This lustrous residue dissolved 

 in HNOg dil. on boiling, and gave the reactions of silver with HC1 and 

 with K 2 Cro 4 . 



(3) Portion dried in a crucible and ignited gave a dark violet 

 residue with metallic lustre. 



Washed with strong H 2 S0 4 the violet portions turned green (trace 

 of Indigo) ; then washed well with H 2 and then digested the residue 

 in NH 4 HO, but nothing was dissolved .\ no Ag 2 0. 



Again washed with H 2 and dissolved in HN"0 3 the solution be- 

 came turbid on adding HC1 dil. and cleared up on adding AmO .-. Ag, 

 confirmed by K 2 O0 4 . 



It thus appears that the portion of the ppt. of the Sodium-silver- 

 indigo compound which is soluble in Ammonia, contains traces of Indigo- 

 blue but the majority of the Indigo is present as one of the Indigo-browns 

 to be hereinafter referred to, decolorizing with HN0 3 with characteristic 

 smell of hyperoxidized Indigo products. 



B. The portion of the Sodium-silver-indigo ppt. which does not dis- 

 solve in NH 4 HO is left on the filter in the form of a fine black powder. 

 This portion was thoroughly washed with weak Ammonia solution and 

 finally with H 2 and dried at 100°C. When dry it formed a very fine 

 grey powder, so fine as not to be capable of being scraped off the filter. 

 Filter digested in boiling HN"0 3 dil. 10% the grey ppt. dissolves to a 

 colourless solution giving the reactions of Ag. No residue left. The 

 ppt. insoluble in NH 4 HO is thus proved to be metallic silver. 



