1 82 OF VIOLET PURPLE DYES. 



both probably It is highly ptobable, thdt these are tannates of iron, diffcr- 



tan nates of ing merely in the proportion of oxigen which they contain, 

 especially as the blue is changed into the black by exposure 

 to the air. 



Ink not well The nature of ink is at present not well understood ; but it 

 is not my intention to undertake its investigation, I leave that 

 task to an abler hand. I beg leave, Sir, to conclude, by pro- 

 posing a few queries for your consideration, and for that of 

 your correspondents. 



Queries res- * n what do new and old writings differ ? 



pectmg its na- I s the difference in consequence of the particles of the old 

 writing having become more firmly united together by time; 

 or is it on account of their having undergone some chemical 

 change*? If the latter, in what does this change consist?. 



Is it the tannate ofiron, which has suffered an alteration ? or 

 is it the gum, which all inks contain ? 



Is it there any substance capable of dissolving, without de- 

 composition, the black tannate of ironf ? 



ture 



VII. 



Of Violet Purple, and the different Tints that may be derived 

 from it; by John Michael HaussmanJ. 



Water not the yy ATER is not the sole menstruum capable of extracting 

 «ruumofdyes. tne colouring parts of plants, in order to enable them to ad- 

 here to alumine or oxide of iron fixed in any cloth. There 

 are vegetables, as alkanct root, which give out their colouring 



* That it is not on account of a chemical action having taken place 

 between the tan and the gelatine of the paper, will appear from this, that 

 unsized paper yields a copy no easier than any other. 



•f From the experiments of Bouillon Lagrange, which render it pro- 

 bable, that strictly there is no such thing as gallic acid, and from the 

 manner in which ink is generally prepared, viz. by long boiling, which 

 must dissipate the acid if it exist, I have been induced to omit taking it 

 into account. 



% Annales deChimie, vol. lx. p, 288, December, 1806. 



matter 



