48 TESTING MISCELLANEOUS SUPPLIES. 



be employed in experiments to ascertain the resistance of a given dye to erasure, 

 as light, heat, and all of the solvents and reagents known to the chemist are 

 available for the use of persons who might desire them for use in assisting 

 them in making fraudulent erasures. 



For the purpose of canceling postage stamps, it is necessary that the cancel- 

 ing marks be substantially indelible, because the inks used in printing many of 

 the stamps are very resistant. Stamping inks used for other purposes, however, 

 do not require absolute indelibility. 



In making the tests use several layers of blotting paper as a pad, pour on 

 this a small quantity of the ink and distribute carefully ; see that all excess has 

 been absorbed by the pad before using the stamp. Make a sufficient number of 

 impressions at one time to suffice for all tests and leave some in reserve. Hav- 

 ing made the impressions, arrange them in groups according to the color and 

 kind of ink, and rank them according to the following scheme : 



1. Of highest rank. 



2. Very good, but not of the best. 



3. Good. 



4. Fair. 



5. Poor. 



Having exposed the impressions to the various reagents, as described herein- 

 after, each sample is again rated according to the effect of the reagents, as 

 follows : 



1. Unaffected. 



2. Slightly affected. 



3. Much affected. 



4. Almost effaced. 



5. Effaced. 



The wet reagents used are pure water, water with the addition of 10 per cent 

 of strong ammonia (sp. gr. 0.90), pure alcohol (95 per cent), alcohol with the 

 addition of 10 per cent of strong ammonium hydroxid, 2 per cent hydrochloric 

 acid, and 200th-normal bleaching powder. Expose each impression in a small 

 Erlenmeyer flask to about 50 cc of the reagent for 24 hours, noting its appear- 

 ance at the end of 15 minutes, 1 hour, and 24 hours. Then rinse, dry, and rate. 



For the sunlight test expose impressions under glass for ten days to direct 

 sun, rating at the end of the third, seventh, and tenth days. The tests with 

 reagents are considered of less use than the other tests, and are not always 

 applied 



RUBBER-STAMP INKS. 

 1. Preparation and Care of Sample. 



The precautions given in regard to the care of samples of inks made with an 

 oil base should be observed. 



2. Change of Weight on Exposure to Air. 



This determination should be conducted in the manner described for the 

 determination of volatile matter in inks made with an oil base. Rubber- 

 stamp inks, however, gain or lose in weight according to the constituents used 

 in their manufacture and according to atmospheric conditions. A rubber- 

 stamp ink should not, however, undergo very much greater changes in weight 

 when exposed to the air under given conditions than diluted glycerin containing 

 75 per cent of glycerin and 25 per cent of water by volume. 



