Writing ink* 
237 
that the strokes made with it by the pen are more clean. To 
me, however, logwood has always seemed to give additional 
body or fulness to the colour of ink, though it cannot be sup- 
posed to render it more lasting ; for, by many experiments, I 
have found, that neither on paper, or parchment, any more 
than on linen, or cotton, or, indeed, wool, was the black re- 
sulting from a combination of logwood and iron, of equal du- 
rability with that from galls and iron. And it may, therefore, 
be best in making ink, to employ, as Chaptal advises, only half 
as much in weight of logwood as of galls. He thinks, also, 
that the addition of sulphate of copper, in the proportion of 
one ounce to every fifteen ounces of galls, produces a good 
effect 3 that the bluish tint which accompanies ink when first 
made, even in the most suitable proportions, (until sufficient 
oxigene has been absorbed) will be sooner overcome by this 
addition, and that it will also contribute to render the ink more 
lasting. 
But of this last effect I am very far from being convinced 5 
because it has been fully ascertained, by experiments which I 
have repeatedly made, that the colouring matter of logwood 
cannot be made so durable upon either paper, wool, silk, linen, 
or cotton, when united to an oxide of copper, as it is with 
that of iron 3 and though, by producing a dark llue with 
copper, it may improve the shade of black resulting from the 
iron and galls, this blue, by fading sooner than the black which 
logwood produces with iron, (when no copper is present,) must 
render the ink so much the less durable. I have here supposed 
the effect of copper to result exclusively from its union with 
the colouring matter of logwood 3 for with that of galls it can 
produce neither blue nor black. 
(To be continued J 
