$a ON VARIOUS CIIKMICAL ACTION*^ 



acid irom its gura, I was too well acquainted with its smell, 

 ftot to have distinguished it in purifying and drying the re* 

 siduums of indigo treated with nitric acid, if my occupa- 

 tions as a manufacturer, which prevent me from gratifying 

 my iuclination for chtTinical experimenls, had not proved an 

 obstacle. Perhaps too I should not have missed the dis- 

 covery of the detonating property of the bitter portJon of 

 the residuum : but it seems I was not born to make a figure 

 I in the career of. discovery, 



Aysenical allca- With respect to the solution of indigo by means of an 

 indjffo*^"^^^" ^ alkaline solution of red arsenic, which is used in calica 

 printing, 1 no longer observe the proportions indicated in 

 my memoir. 1 simply make a caustic alkaline solution of 

 red arsenic, to which I add, while it is yet boiling, a suf- 

 ficient quantity of brayed indigo, to obtain a very deep 

 shade, which it is easy to render lighter afterward, ac- 

 cording to the object proposed, by diluting the solution of 

 indigo with a weak lixivium of caustic potash. Tliis 

 i$ preferable to pure water, because it retards in some 

 measure the absorption of oxigen froaii the al-mosph^.re, 

 and cOnseq;U<3ntIy the regeneration of the indigo. The 

 Cav.t:onsre- beauty of the blue in the ; calicoes requires, that this 

 pifcation!'^^*^^"^^^^^'***^'^ should be neither too slow nor too speedy. 

 The too slow absorptijon arising from too great exteiss ©€ 

 caustic alkali ought to be avoided in pencilling blues, as weM 

 as in the blues in block- printing, which are procured by 

 passing the goods, first printed with bra/ed. indigo miwed 

 with a gummy solutioti of sulphate of iron, alternately 

 through vats of caustic potash, water, siilphate of iron at 

 a minimum of oxidation, and lastly a vat acidulated by 

 sulphuric or muriatic acid. 



Indigo and mw- On e?[posine to a sand-heat a mixture of brayed indiffa 

 tiate of tin. . ^ . . . • ^ . . , , . . . 



With a muriatic Solution of tin oxided at a mimmum, m 



which there is an excess of acid, the colouring substance is 

 decomposed, occasioning the evolution of a gas-of an in- 

 supportable and noxious smell, whlcli deserves to be 

 examined. 

 Eulphate of in- . Jf indigo treated with the muriatie solution of tin oxided 

 mteoi^tiii" at .> minimum, without the assistance of a caustic alkali, 

 f cirinot be of. aiiy. use -in .d)dng, it is not the same with 



sulphate 



