480 PAPER, INDELIBLE CHEQUE 



Chrome yellow is also frequently used, as well as tbo terra di Sienna and yellow 

 ochre. 



3. Reds are almost exclusively decoctions of Brazil-wood. 



4. Blues are either Prussian blue or blue verditer. 



5. Greens are : Scheele's green, a combination of arsenious acid and oxide of 

 copper ; the green of Schweinfurth, or green verditer ; as also a mixture of blues and 

 yellows. The use of arsenic in paper-hangings has of late (1859) been the subject of 

 much discussion, and many absurd statements have been made respecting its injurious 

 effects. See ARSENIC. 



It has been suggested by Piesse that paper variously coloured in the pulp may havo 

 designs printed upon them after the same manner as calicos are printed, sometimes by 

 n discharge-mordant, or by chemical reagents applied by an engraved roller, so as to 

 modify the colour of the pulp. 



6. Violets are produced by a mixture of a blue and red in various proportions, or 

 they may be obtained directly by mixing a decoction of logwood with alum. 



7. Browns, Blacks, and Grfeys. Umber furnishes the brown tints. Blacks are 

 either common ivory- or Frankfort black ; and greys are formed by mixture of Prus- 

 sian blue and Spanish white. 



All the colours are rendered adhesive and consistent by being worked up with 

 gelatinous size or a weak solution of glue, liquefied in a kettle. Many of the colours 

 are previously thickened, however with starch. Sometimes coloured lakes are employed. 

 PAPER, INDELIBLE CHEQUE. The facility with which ordinary-written 

 characters can be expunged from paper by chemical bleaching-liquids, acids, and 

 alkalis, has led to the adoption by bankers, for their cheques and drafts, of papers 

 which present obstacles to the fraudulent alteration of the amount and intent of these 

 documents. 



Instances of this description of forgery have occasionally occurred. In the spring 

 of 1859 a cheque was paid at a branch of the Bank of England in which both the 

 amount had been altered and the crossing extracted by chemical means. 



In 1822 William Robson patented a method of securing bankers' cheques by 

 printing upon their surface vegetable colours equally fugitive with common writing-ink. 



This method, and its extension to the tinting of writing-papers in the pulp, has 

 been generally adopted by bankers. Those papers which exhibit the perfection of 

 Robson's principle are limited in practice almost exclusively to certain tints obtained 

 from logwood. 



Mr. Baildon's paper is a tinted one, from which the colour is removed. The 

 patentee states that he offers absolute integrity and security from alteration for any 

 document once issued ; and this is obtained by a fluid or ink, which, when used, 

 becomes, in fact, a permanent dye, different from any inks yet introduced for this 

 purpose, which are pigments. The least attempt to tamper with the ink or paper is 

 instantly detected by a dark stain in the paper, which can never be removed. 



As early as 1817 Gabriel Tigere patented a method of manufacturing 'writing- 

 paper from which it would be extremely difficult, if not impossible, afterwards to 

 extract or discharge any writing from such paper.' This paper was impregnated 

 during the sizing process with the ferrocyanide of potassium. 



Mr. William Stone's patent, 1851, was an effort to supply the deficiencies of this 

 method. He added a solution of cyanide of potassium and starch to the ferro- or 

 ferridcyanide of potassium. This method has been fully carried out into practice, 

 but it failed to give the complete security desired. The chemical defects of Tigere's 

 method may be stated thus : Although admirable in the protection it affords against 

 the application of acids, it is powerless to resist the bleaching-powers of such sub- 

 stances as common chloride of lime (bleaching-powder) in solution ; and the ink may 

 also be removed by the application of either of the caustic alkalis. In Stone's method, 

 although by the application of bleaching agents containing chlorine the paper is 

 stained by the blue compound termed the iodide of starch, this is removed again by 

 the application of an alkali. 



The Linen Company Bank of Scotland employ green-coloured cheque-piper, on 

 which the sum drawn is written for with a discharge-ink. 



In 1837 David Stevenson patented the manufacture of a paper which ho specified 

 as containing ' a solution of manganese, mixed with a solution of prussiate of potassa 

 in a liquid form, and mixed with the pulp whereof the writing-paper is to be made.' 



In June 1859, Mr. Robert Barclay patented a process of manufacturing a white 

 writing-paper, on which writing-ink is stated to be unalterable for fraudulent pur- 

 poses by any existing chemical process. He incorporates in the paper an insoluble 

 1'errocyanide and an insoluble salt of manganese, and provides against the discolora- 

 tion of the paper in the sizing process (which has been a serious objection in practice 

 to the xise of the ferrocyanide of potassium) by discarding the use of alum, and sizing 



