112 Mr. Reid on Writing-ink, and on the Effects 



upon the ink, equally as much depends upon the material 

 upon which it is written ; for as ink readily suffers decomposi- 

 tion by the application of chemical agents, and as paper and 

 parchment contain ingredients which affect its composition, it 

 is necessary to attend to the circumstances connected with the 

 latter subject, as well as those which have reference to the 

 chemical constitution of the ink itself. 



With regard to the composition of ink, it appears that for- 

 merly galls, gum, and sulphate of iron had been used in ma- 

 nufacturing it. A decoction of the galls was generally made, 

 to which the gum and sulphate of iron vvere afterwards added. 

 After some time a sediment falling down, the fluid was poured 

 off, which gradually absorbed oxygen from the air; when it was 

 fit for use. 



In this manner, when the proper proportions are observed, 

 may writing-ink be made — of which it may be affirmed, that if 

 it does not keep its colour so well as we see that ink on old 

 writings does, it is owing entirely to some circumstance con- 

 nected with the material upon which it is written, the nature 

 of which I shall afterwards endeavour to describe ; and as this 

 process forms the basis of those still employed, I shall avail 

 myself of it to point out what appears to me erroneous in the 

 opinions commonly entertained on the subject, and how it may 

 be improved so as to increase the quantity of ink which may 

 be obtained from a given portion of the galls. 



If to a solution of galls, sulphate of iron with or without 

 trum is added, and the compound is excluded from the air, 

 it is dissolved ; but no change of colour results, and no preci- 

 pitate is deposited. Hence it is to be inferred, that oxygen is 

 necessary in order that that change may take place from which 

 results the peculiar compound called ink. But when the air 

 is admitted, the precipitate begins to be formed in the course 

 of a minute, and the colour gradually deepens. What is the 

 nature of the compound which remains ? Chemists have de- 

 scribed it as consisting of minute particles of colouring mat- 

 ter formed of tannin and gallic acid, combined with sulphate 

 of iron suspended in the fluid by means of the gum. But in 

 opposition to this opinion, it may be remarked, that no colour- 

 ing matter is deposited from it when gum is not used. It 

 may be filtered again and again, without the loss of any part 

 of it. It is therefore a solution. But though the gum does 

 not serve the purpose which has been supposed, it is not- 

 withstanding a useful ingredient. Ink made without gum, 

 sugar, or some other ingredient of a similar nature, is pale ; 

 but any of them, when present, combining with it, gives to it 



intensity 



