iO On a Colour Jor markhig the J^nds cj Cottofi 



rendered caustic with half a part of quicklijne. The pre- 

 cipitation of the oxi'.le of manganese from marks, by one 

 or the other of these alkahnc leys, will take place (allowing 

 for its coloration by the lamp black) under the colour of a 

 yellowish while, which will gradually turn brown by the 

 attraction of the oxvgcn of the atmospheric air. The al- 

 teration of these maiks to brown will take place very spee- 

 dily, and even with a stronger intensity, approaching to 

 black, if you bleach by means of an alkaline oxygenated 

 muriatic ley, the cloths, the ends of which have been 

 plunged for a few minutes into any kind of alkaline ley 

 whatever. These marks of brown oxide of manganese re-, 

 sist, not only all the processes of bleaching, and all acids 

 of the strencth required by them, but likewise the more 

 complicated processes employed in printing cloths. 



Exp. II. Had not acetic acid more affinity for manga- 

 nese than for iron, and were it not disengaged as easily 

 from acetate of manganese as from the acetic solution of 

 iron, by evaporation and desiccation, inalterable marks 

 miffht be procured in the most simple manner, by causing 

 ihe oxide of manganese to adhere to stuffs by means of 

 acetic acid, and afterwards exposing that oxide to the at- 

 traction and saturation of the oxygen of the atmospheric 

 air. The acetic tikissolution of manganese may very 

 speedily be obtained by mixing, in suitable proportions, 

 acetate of lead with a solution of sulphate of manga- 

 nese; but as this acetic solution possesses no advantage 

 over the sulphate of manganese for marking stuffs, as it is 

 necessarv, before it can be used, to subject it in every re- 

 spect to the treatment described in Exp. I., and as it is 

 nuich dearer, it is not adviseable to en)ploy it. 



Exp. III. Two ounces of sulphate of manganese dis- 

 solved in eight ounces of acetic solution of iron, concen- 

 trated to twenty decrees, furnish, when thickened with 

 one-fortitth part of gum-dragon, a deep yellow colour, 

 which graduallv turns to a brown if treated exactly in the 

 manner described in pLxp. I. The acetic solution of iron 

 affords for the rest no other advantage than that of causing 

 the colour of the marks to dry rather more speedily ; for the 

 oxide of iron dissolves more or less rapidly in acids, in pro- 

 portion to its state of oxygenation or oxidation. I prefer 

 gum-dracon for thickening marking colours to the other 

 gums and to starch, because those substances weaken the 

 colours too much by their interposition : if, how ever, in 

 the marking of coarse cloths, gum-dragon should be at- 

 tended with any difficulties, it would then be necessary to 

 have recourse to starch, 



Exp. 



