Sigg C0MPARIS6T^ OF DIFFfiRENT KINDS OF ALUM. 



After they were dyed,' we found in the series of tints ex- 

 . peiiments 56 aiid 57> produced by our pare alum rendered 

 more or less ferruginous, colours perfectly similar to those 

 of our ordinary alums. Thus ^^V^ part of sulphate of iron 

 added to this pure alum, afforded us with weld and cochineal 

 , the same colours as Roman alum ; -■^'^tt the same as the 

 alums of Bouvier and Curaudau; ttVit ^^^ same as that of 

 Javelle; and tAtt the same as that of Liege. 

 J he different We can no longer therefore ascribe the differences we ob- 

 ow^ncto 1^"^ *^^"^^ ^^ clyeing with different alums to. any other cause, 

 than these infinitely small quantities of sulphate of iron ; 

 since, by adding this substance, we converted purified and 

 Roman alum into alums, which gave us the same results 

 with reagents as the most impure kinds of the shops; and. 

 On the contrary, by abstracting the sulphate of iron, we could 

 make at pleasure, from the most impure kinds, alums pro- 

 ducing as fine or finer colours than those obtained with 

 Roman alum. 



Art. IV. Experiments on the injiuence of sulphate of ammo^ 

 nia, and of alum with an nmmoniacal base. 



Experiments Many distinguished chemists have asserted on the autho- 

 with sulphate ^^^ ^^ Ber^rman, that alums with an ammoniacal base are 

 «>t ammonia. ... . . . rn • i i i • • • 



mjurious m dyemg. 1 o ascertam whether this opinion were 



well founded, we treated wool and silk with several propor- 

 tions of sulphate of ammonia, which we added to Roman 

 alum, and with alum without potash, having its base entirely 

 of alumine and ammonia, 

 it produced no _».^ and j^y of sulphate of ammonia produced no percep- 

 fcjtec , tible change in silk or wool with weld or cochineal colours, 



unless in consi- ^i^.^ „>_., x, and V of this salt produced a regular degrada- 

 Vtv^ ^ quan- ^-Qj^^ -j^ which the colour with Roman alum and -y its weight 

 of sulphate of ammonia was two or three shades weaker than 

 t^iat with Roman alum alone. 

 Common Hence we had reason to expect evident changes from alum 



alums not in- with an ammoniacal base, but we found no difference in its 

 iured by this. ^^^^^ ^^^ ^^,^^ ^^ Roman alum. 



Wool 



