For the determination of the ash, place 2 to 3 grams of the ink in a porcelain dish, 

 which must be of such size as to avoid loss of ink due to the foaming which is likely to 

 attend the beginning of the incineration. Heat the dishes thus charged in a muffle at a 

 low red heat, until all organic matter and uncombined carbon have been burned. Cool 

 and weigh. 



If an excessive percentage of ash is found, the percentage of mineral matter con- 

 tained in the alcoholic extract should be determined by incineration of the residue 

 obtained after evaporation of this extract. If either the total ash or the ash of the alco- 

 holic extract is high, a qualitative examination should be made. 



7. RESISTANCE OP PIGMENTS AND DYES TO LIGHT AND REAGENTS. 



It is necessary in the case of canceling inks, and important, if not necessary, in the 

 case of many stamping inks, that the pigments and dyes employed in their manufacture 

 be as resistant as possible to means which may be employed for the erasure of marks 

 made by them on paper. Under this heading may be mentioned also the importance 

 of the use of dyes which possess considerable affinity for vegetable fibers. It is not 

 practicable to enumerate the agents which should 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 canceling marks 

 be substantially indelible, because the inks used in printing many of the stpmps are 

 very resistant. Stamping inks used for other purposes, however, do not require abso- 

 lute indelibility. 



II. METHODS FOR THE 'INVESTIGATION OF RUBBER-STAMP INKS. 

 ]. 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 determina- 

 tion 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. 



3. PENETRATING POWER. 



This test should be conducted in the manner described above for inks made with an 

 oil base. . 



4. SEDIMENTATION TEST. 



This test should l/e conducted as described for inks made with an oil base, with 

 the exception that the portions of ink should be diluted with water instead of petro- 

 leum ether. 



5. DETERMINATION OF LAMPBLACK AND OTHER CONSTITUENTS. 



A scheme of analysis similar to that described above for inks made with an oil 

 base should be employed. Some experiments will be necessary in most cases to 

 ascertain the proper solvent to be used in the case of each sample of ink to be exam 

 ined. Alcohol, however, will generally be found to be satisfactory for rubber-stamp 

 inks. 



[Cir. 12] 



