i88i.] 
A Safety Paper for Cheques. 105 
put the question in such a manner that the applicant’s 
purpose would never be suspected. When once the writing 
in the body of the cheque has been effaced, the paper is 
re-sized and such a sum filled in as amply repays the operator 
for his trouble. 
It must not be supposed that bankers have made no at- 
tempts to defend themselves against this fraud. Colouring 
matters calculated to be affedted by any agent supposed 
capable of discharging writing inks have been mixed with 
the paper pulp, and applied in various designs to the 
face and the reverse of the documents. Before us lies a 
cheque which has been filled up experimentally for the pur- 
pose of testing those supposed safeguards. The paper itself 
contains Prussian blue, produced by successively treating 
the pulp with potassium ferrocyanide and with a per-salt of 
iron. This tinting is intended to detedt the application of 
any alkali which would decompose the Prussian blue and 
produce in the place of a blue tint a rusty yellow. On the 
reverse side of the cheque is a design in ultramarine, a pig- 
ment easily destroyed by acids, while on the face the name 
of the bank and the space to receive the writing are executed 
in an aniline violet. It may perhaps surprise the non-chemical 
public to be told that these precautions can be overcome. 
Such, however, is the case. The words “ eighty-seven 
pounds,” and the figures, “ £87 o o,” for which sum the 
cheque was filled up, have been completely effaced, leaving 
the name of the payee and the word “ Specimen,” written 
where the signature would stand, untouched. Not only so, 
but the general tone of the paper, the ultramarine design, 
and the violet tinting on the face are unaltered. A gentle- 
man of great experience in the tindtorial arts, and accus- 
tomed to detedt the slightest difference in colours, declares 
on comparing the effaced cheque with one in its original 
condition that he could not detect any alteration. 
The invention which we are endeavouring to expound, and 
which is due to the ingenuity of Mr. A. A. Nesbit, F.C.S., 
takes a point of departure at once novel, and yet as simple 
as the egg of Columbus. Every chemist knows that there 
are colours, of which litmus may be taken as a type, which 
are capable of being modified both by acids and by alkalis, 
but in a different manner. Suppose the cheque is first 
coloured a pale uniform greyish blue with neutral litmus. If 
we then print upon this with a dilute acid we shall produce 
red letters, lines, or devices. By a second application, of 
an alkaline liquid, we produce decided blue lines or devices, 
which may be interwoven with the former. We then fill 
VOL. III. (third series.) 1 
