$24 OLservations on the Use of StahVs 



coction of logwoodj without yellow berries^ gives a choco- 

 late colour. 



If this dye be diluted with a sufficient quantity of water, 

 all the oxide falls to the bottom. When edulcorated, fil- 

 tered, and brought to a white heat in a crucible, this oxide 

 polishes steel as coniplej;ely as the English colcothar. 



Linen or worsted yarn imbibed with this dye, and then, 

 immersed in a dye-liquor prepared with caustic alkali, 

 which precipitates the oxide of iron, acquires by this pro- 

 cess a much darker yellow than w hen it is left at rest for 

 twenty-four hours, and then dried and washed. 



Every drop of a solution of caustic alkali applied to this 

 dye precipitates from it a part of the oxide as it overcomes 

 the carbonic acid. By these means it is completely de- 

 composed ; and this oxide, when washed and exposed to 

 heat for a sufficient time, gives a verv tine polish to steel. 



This dye, as I have already said, is nothing else than a 

 solution of hyperoxvgenated carbonate of iron by an alka- 

 line carbonate, which serves it as a vehicle ; only care must 

 be taken not to add too much when dark colours are re- 

 quired. 



All solutions of iron sufficiently oxvgenated, treated 

 with an alkaline carbonate in the same manner as the 

 nitrous solution of iron, are capable of producing a similar 

 dye. I have convinced myself of this fact by employing 

 the acetic, muriatic, and sulphuric acids for this purpose. 

 The latter I obtained in two ways : in one I dissolved sul- 

 phate of iron in nitrous acid, and, when the effervescence 

 and disengagement of nitrous gas had ceased, subjected it 

 to evaporation : in the other, I proceeded according to the 

 process which I gave in my paper on the artificial prepara- 

 tion of volatile alkali, published in the Journal de Physique 

 for June 1787 ; that is, by suffering the solution of sulphate 

 of iron to absorb nitrous gas. By both solutions I obtained 

 a hyperoxygenatcd acetous solution of iron, as I decom- 

 posed it by acetate of lead. 



A nitrous solution of copper, prepared from nine pounds 

 green oxide of copper, nine pounds of water, and three 

 pounds cream of tartar, with a solution of carbonate of 

 potash, and treated as the nitrous solution of iron, pro- 

 duces the same effects. When mixed with gum, and im- 

 printed on woollen or cotton stufi's, it deposits the oxide of 

 copper of a beautiful green tint. A gummed ammoniacal 

 solution of copper may be employed in its stead ; for when 

 the cloth is dried the ammonia is diseneraged from it, and 



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