A calcination of the sulphate of iron, which Chaptal, Proust, and some others have recommended, Dr. Bancroft does not regard as of much importance; for, he says, though the ink may be thereby made to attain its utmost degree of darkness, almost immediately, yet the strong disposition which ink has to absorb oxygen from the atmosphere until saturated therewith, will enable it, without such calcination, to attain an equal degree of blackness, in a day or two, according to the temperature of the air, if the latter be allowed free access to it. For reasons which he also states, he omits the sulphate of copper; though he observes that, if any portion of that metal were deemed beneficial, he should prefer verdigrise to the sulphate, the latter containing a much larger proportion of acid than even the sulphate of iron, and being, therefore, more likely to render the ink corrosive. He regards gum as highly useful to retard the separation and subsidence of its black part, or compound of colouring matter and iron, previous to its application to paper, as well as to hinder it, when used, from spreading and penetrating too far.
Indelible Writing Ink.
M. Chaptal remarks, that, since the oxygenated muriatic acid had been found capable of discharging the colour of common writing ink, both from parchment and paper, without injuring their texture, it had been fraudulently employed to efface particular parts or words of deeds, contracts, or other writings, for which others had been substituted, leaving the signatures untouched. In consequence of these frauds, the commercial parts of society, as well as governments, were solicitous for the discovery of some composition, which might be employed instead of common writing ink, without its defects; therefore Chaptal, (being then minister of the interior of France, and possessed of great chemical science,) as might be expected, occupied himself particularly with that subject; and he states, that up to the then present time, the composition which had been found most useful for this purpose, consisted of a solution of glue in water, with which a sufficient portion of lamp black and a little sea salt were intimately mixed, by rubbing them together on marble. This composition was made sufficiently thin by water, to flow readily from the pen; and he describes it as being capable of resisting the action, not merely of cold, but of boiling water, and also of acids, alkalies, and spirit of wine; and attended with no inconvenience but that of abrasion by being rubbed.
It is observed by Dr. Bancroft, that when lamp black has been incorporated with common ink, by first rubbing the former in a mortar with a mucilage of gum arabic, the writing done with it could not be rendered invisible by the application of muriatic acid; and, doubtless, such an addition of lamp black would hinder the letters from ever becoming illegible by age, at least within any length of time which the paper and parchment could be expected to last. But ink made with this addition would require to be frequently shaken or stirred, as the lamp black would otherwise be apt to separate and subside.
In the making of indelible ink, the [receipt] for lamp black before given may be of considerable importance.
Calico Printing.
Perhaps no object has more engaged “the ingenious chemist’s art” than this, and leave is craved to conclude this diversion from the mayoralty seal of London, by what may be serviceable to some who are actively engaged in an extensive branch, from whence our private chambers, and the dresses of our wives and daughters, derive continual improvement.
Prosubstantive, or Chemical Black, for Calico Printers.
“Some years ago,” says Dr. Bancroft, “I purchased of a calico printer, possessing great knowledge of the principles and practice of his art, the secret of a composition which he had employed with success, as a prosubstantive black, and which, as far as I can judge from experiments upon a small scale, deserved the high commendations which he bestowed upon it: and though I have never obtained the smallest pecuniary advantage from this purchase, in any way, I will here give the full benefit of it to the public. The following was his recipe, with some abbreviations of language: viz. Take two pounds of the best mixed galls, in powder, and boil them in one gallon of vinegar, until their soluble part is extracted, or dissolved; then strain off the clear decoction, and add to the residuum of the galls as much water as will be equal to the vinegar evaporated in boiling; stir them a little, and after allowing the powdered galls time to subside, strain off the clear liquor, and mix it with the former decoction, adding to the mixture six ounces of sulphate of iron; and this being dissolved, put to it six ounces more of sulphate of iron, after it has been previously mixed with, and dissolved by, half of its weight of single aquafortis; let this be stirred, and equally dispersed through the mixture, which is to be thickened by dissolving therein a sufficient quantity of gum tragacanth, (of which a very small proportion will suffice.) Calico, after being printed or pencilled with this mixture, should, when the latter is sufficiently dried, be washed in lime water, to remove the gum and superfluous colour, and then either streamed or well rinsed in clear water. This composition has not been found to weaken, or injure, the texture of calico printed or pencilled with it, and the colour is thought unobjectionable in regard to its blackness and durability.”