166 Proceedings of the 



discharged from papers and other documents, either for the purpose 

 of falsifying the contents, or for making a second and fraudulent use 

 of old stamps. With this view, the Academy of Sciences was 

 directed to take the subject into consideration ; and a committee, 

 consisting- of MM. Gay Lussac, Dulong, Chaptal, Deyeux, Thenard, 

 D'Arcet, Chevreuil, and Serullas, was appointed for the purpose. 

 The attention of the public was called to the subject, and a great 

 number of specimens of ink, alleged to be indelible, were forwarded 

 to the committee. Numerous experiments were made ; and on the 

 30th of May and 6th of June the report was read to the Academy 

 by M. D'Arcet. It is unnecessary for our purpose to follow the 

 reporter through his elaborate history of the different manufactures 

 of ink in different ages, or the detail of the experiments made with 

 the various samples submitted to the committee : it is sufficient to 

 state the conclusions, which were unanimously adopted as the 

 results of the investigation. These were, that the falsification of 

 written documents will be fully prevented by the use of ink prepared 

 in either of the two following manners. 1. Indian ink (or, in its 

 absence, the imitation of it made in Europe with soot and animal glue 

 or gum), dissolved in a mixture of water and muriatic acid, of the 

 specific gravity of 1010 (li degree of Beaume"s instrument.) This 

 ink may be prepared for fourpence English per quart. 2. To a solution 

 of acetate of manganese, of the specific gravity of 1074 (10 degrees 

 of Beaume), add half its volume of solution of carbonate of soda 

 crystallized, saturating it at about 166 percent. : dissolve Indian ink 

 in this liquid, and writing traced with it will become perfectly inde- 

 lible on being exposed to the action of the vapour of liquid ammonia. 

 The committee lay down, as a general principle, that no ink, kept 

 in a liquid state, can be indelible, as the colouring matter, from its 

 excess of density, will necessarily be deposited. Additional security 

 will be obtained by writing on paper so prepared, that even if the 

 ink could be discharged, it would necessarily be seen that it had 

 been so discharged. Thus, M. Coulier proposes a paper, having 

 printed on each sheet, lines and patterns, so complicated, as to defy 

 forgery, and struck off from a steel plate damasked with aqua-fortis. 

 The ink with which this is printed would be discharged by chlorine, 

 so that the superjacent writing cannot be destroyed without also de- 

 stroying the drawing. This plan is excellent for bills of exchange 

 and other small documents ; but from the expense and delay occa- 

 sioned by the engraving and printing, the designs would be ill 

 adapted for legal proceedings and public documents. M. Chevallier 

 proposes a paper coloured in the pulp with colours liable to be dis- 

 charged by all the known re-agents, but this might easily be re- 

 coloured when the alteration is made. M. Maimu suggests adding 

 to the pulp of the paper filaments of wool, cotton, or hemp, dyed of 

 different colours, some of which will be acted on by the acids, and 

 others by the alkalies, but all liable to be discharged by chlorine. 

 When these colours are discharged, it is almost impossible to restore 

 them ; but the writing may, in some cases, be effaced without any 



