No more interesting illustration of the effect of the composition of old inks upon the permanency of writing can be found than in the various names written in Milton's family Bible, to be seen in the British Museum. It will be noticed that all the entries of the births of himself and the members of his family are in the handwriting of Milton, and that with one exception all the inks are of a good dark tone. The exception is seen in the entry relating to the birth of his daughter Deborah "on the 2nd of May, being Sunday, somewhat before three of the clock in the morning, 1652." Here the ink has faded to a faint brown tint. Considerable variations are possible in the proportions of galls and iron that may be used without interfering with the blackness of the pigment, but a deficiency of tannin outside those limits will cause the writing to turn brown. A lack of tannin to combine with the excess of iron present is probably the explanation of this faded entry in Milton's Bible. It is very probable, too, that tests applied to the freshly-written entries would have shown that the ink in this entry was of different composition from that of the inks in the other entries. Lovibond's tintometer, an instrument which enables slight differences of colour to be distinguished more accurately than is possible with the naked eye, has been used in matching the colour obtained in chemical reactions with those given by the colour scales prepared from known or suspected inks. For recording colour, strips of glass graduated so as to form a series of colour scales are employed in this instrument, and in this way a note can be taken of any given tint. [Illustration: The Tintometer] The first occasion upon which this instrument was employed in criminal work was in the Brinkley poisoning case, in which the colours of the different inks upon the will and other documents were examined by its means. The problem of determining the age of an ink in writing is much more difficult than that of deciding whether two writings are in the same or in a different kind of ink. It is, as a rule, possible to distinguish, with the aid of the microscope and tintometer, between freshly-written and old writing up to about the sixth day, after which the black pigment has attained sufficient intensity to prevent further differentiation until after the lapse of two or three years or more, when the provisional pigment will have faded or have become fixed by the iron tannate. In most cases the provisional pigments used offer greater resistance to the action of chemicals, but are infinitely less stable than the iron tannate when exposed to the action of light and air, and eloquent testimony to this difference is given by the comparison of certain manuscripts of the seventh and eighth centuries with typewritten matter in aniline ink, which has been put aside for a few years.