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their own； according to the most approved
and expensive formulas。
〃Manuscripts of the eleventh and twelfth centuries
now in the state paper office of Great Britain；
are apparently as bright as when first written；
while those of the last two hundred years are more
or less illegible； and some of them entirely obliterated。〃
While the information sought to be conveyed in the
last statement may be in some respects correct； it must
be remembered that most of the MSS。 extant dating before
the thirteenth century were written in 〃Indian〃
ink； while the great majority of those of the last two
hundred years were not； and this fact alone would
account to some extent for the differences mentioned。
The German （Prussian） government in 1859； as the
result of an investigation； employed what they termed
〃Official Ink of the First Class；〃 i。 e。； a straight tanno…
gallate of iron ink without added color； and if permanence
were required as against removal by chemicals；
it was accomplished by writing on paper saturated
with chromates and ultramarine。
In 1871 Professor Wattenbach of Germany published
a treatise entitled 〃Archives during the Middle
Ages；〃 which has some valuable references to the color
phenomena of inks。
William Inglis Clark in 1879 submitted to the Edinburgh
University a thesis entitled 〃An Attempt to
Place the Manufacture of Ink on a Scientific Basis；〃
and which very justly received the commendation of
the University authorities。 His researches and rational
deductions are of the greatest possible value
judged from a scientific standpoint。 The introduction
of blue…black ink is a phase of the development towards
modern methods which he discusses at much
length。
The object of adding a dye in moderation； he
asserts； is to give temporary color to the ink and
where indigo…paste is used； it has been assumed that
it kept the iron gallo…tannate in solution； whereas any
virtue of this kind which indigo…paste possesses is
more likely due to the sulphuric acid which it contains
than to the indigo itself。 The essential part of the
paste required is the sulpho…indigodate of sodium； now
commonly called indigo…carmine。 He further remarks
that the stability of an ink precipitate depends upon
the amount of iron which it contains and which on no
account should be less than eight per cent； he adds
rightly； if gallic acid be preferably used in substitution
for tannin； 〃no precipitate is obtained under
precisely similar conditions。〃 This point followed up
explains in a measure why a gall infusion prepared
with hot water is not suitable for a blue…black； while
a cold water infusion is。 In the latter case a
comparatively small percentage of tannin is extracted
from the galls； while much is extracted with hot water
and the consequence is； on adding the indigo blue the
color is not brought out as it should be。 Substantially
the same thing occurs with ink made with the respective
acids； although the blue color remains for a time unimpaired
in the tannin ink； apparently due to the fact that
ferrous…tannate reduces indigo blue to indigo white； a
change which the low reducing power of ferrous…
gallate does little to effect。 The vegetable matter in
common inks facilitates the destruction； or rather
alteration and precipitation of the indigo； for the dye
appears in the iron precipitate and may be extracted
from it with boiling water。
Dr。 Clark's investigations seek to demonstrate the
superiority of tannin and gallic acid over infusions of
the natural galls； and he undertakes to determine the
correct ratio of tannin and sulphate of iron to be used
as ink。 His experiments in this line show that：
1。 The amount of precipitate increases as the proportion
of iron to tannin is increased。
2。 The composition of the precipitate is so valuable
as to preclude the possibility of its being a definite
body。 Increase of iron in the solution has not at first
any effect on the composition of the precipitate； but
afterwards iron is found in it in greater but not proportional
amount。
3。 At one point the proportions of iron in the precipitate
and in solution are the same； and this is at
between 6 and 10 parts of iron to 100 parts of tannin。
4。 The proportion of iron in the precipitate varies
greatly with the length of time the ink has been exposed。
At first the precipitate contains 10 per cent
of iron； but by and by a new one having only 7。5
per cent is formed； and in from forty to seventy days
we find one of 5。7 per cent。 Simultaneously iron increases
in the ink （proportionate to the tannin）。
5。 The results show； and practice confirms； that
16 parts of iron （80 ferrous sulphate） and 100 parts of
tannin are best for ink manufacture。
The research now travelled in a direction which
accumulating experience showed to be obligatory。
Blue…black tannin ink lost color； and the reducing
nature of the tannin tended to the formation of a
highly objectionable precipitate in the ink； which
made writing anything but a pleasure。 These two
faults were doubtless linked together in some way
and seemed not to exist when gallic acid was used；
for ink so made was found to precipitate only after
a long exposure； it required no free acid to keep the
precipitate in solution； and retained the indigo blue
color for a long time； alkalis did not decompose the
ink； and provided blacker and more permanent writing。
Determination of the correct proportions of
gallic acid and ferrous…sulphate was the subject of prolonged
experiments conducted on similar lines to those
already detailed。 The conclusions as to precipitation
were also similar。 Thirty parts of iron （150 of ferrous…
sulphate） and 100 parts of gallic acid were found to
be the most suitable proportions for ink…making。 It
is advisable； however； not to discard tannin altogether；
owing to the slow blackening of the gallic acid ink；
and a little tannin gives initial blackening and body；
while it is absolutely necessary for copying ink。
Initial blackness can also be ensured by oxidizing
21 per cent of the ferrous…sulphate without adding
the extra acid necessary to the formation of a ferric
salt。
The concluding portion of his research is devoted
to the influence of sugar upon the permanence of ink；
and the results of the experiments are summed up in
the following sentences： 〃It would be injurious to
add 3 per cent of sugar to a tan in ink； while from
4 to 10 per cent would be quite allowable。 Most
copying inks contain about 3。5 per cent of sugar
not far from the critical amount。 With gallic acid
more than 3 per cent of sugar hardly varies the precipitate；
but the importance of this point is somewhat
diminished by the fact that the presence of sugar is
by no means necessary in a writing ink。 Dextrin is
a much superior substance to use。 Curiously this
body rapidly precipitates a tannin ink； hence it is
useless for