“Although my experiments were not always carried on under the most favorable circumstances, their results were eminently satisfactory and will prove a boon to the banking and business world.  A piece of paper was handed to me for the purpose of determining if part of it had been wet and if another part of it had been manipulated for the purpose of erasing marks upon it; in other words, whether this part had been rubbed.  The sample I had to work upon had already gone through several experiments.  I had remarked that the tint of the paper exposed to the vapor of iodine differs from that which this same paper assumes when it has been wet first and dried afterwards.  In addition to this I realized that when sized and calendered paper, first partially wet and then dried, is subjected to the action of iodine vapor, the parts which have been wet take on a violet tint, while those which had not been moistened became either discolored or brown.  The intensity of the coloration naturally varied according to the length of time for which the paper was exposed to the iodine.

“There is a very striking difference also when the water is sprinkled on the paper and the drops are left to dry off by themselves in order not to alter the surface of the paper.

“Thorough wetting of the paper will cause the sprinkled spots to turn a heavy violet-blue color when exposed to vapor while the parts which are untouched by the water will become blue.

“If, after sprinkling upon a piece of paper and evaporating the drops thereon, this piece of paper is thoroughly wet, then dried and subjected to the action of iodine, the traces of the first drops will remain distinguishable whether the paper is dry or not.  In the latter case the trace of the first sprinkling will hardly be distinguishable so long as the moisture is not entirely got rid of; but as soon as complete dryness is effected their outlines, although very faint, will show plainly on the darker ground surrounding the spot covered by the first drop.

“In this reaction, water plays virtually the part of a sympathetic fluid, and tracing the characters with water on sized and calendered paper, the writing will show perfectly plain when the paper is dried and exposed to action of iodine vapor.  The brownish violet shade on a yellowish ground will evolve to a dark blue on a light blue ground after wetting.  These characters disappear immediately under the action of sulphurous acid, but will reappear after the first discoloration provided the paper has not been wet and the discoloration has been effected by the use of sulphurous acid gas.

“The process, therefore, affords means for tracing characters which become legible and can be caused to disappear, but at will to reappear again, or which can be used for one time only and be canceled forever afterwards.

“The usual method of verifying whether paper has been rubbed is to examine it as to its transparency.  If the erasure has been so great as to remove a considerable portion of the paper, the erased surface is of greater translucency; but if the erasure has been effected with great care, examining same close to a light will disclose it; the erased part being duller than the surrounding surface because of the partial upheaval of the fibers.