MATERIALS FOR STAMPING INKS, ETC. 49 



3. Penetrating Power. 



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

 oil base. 



4. Sedimentation Test. 



This test should be 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 with organic solvents. 



5. Determination of Lampblack and Other Constituents. 



A scheme of analysis similar to that described 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 

 examined. Alcohol, however, will generally be found to be satisfactory for 

 rubber-stamp inks. This test is difficult and can not be carried out without a 

 slight loss. To make the loss as small as possible use a very thick felt of asbes- 

 tos and make the filtration continuous never allow the gooch to run empty ; if 

 this occurs it is generally better to repeat the test. 



6. Besistance to Light and Reagents. 



The remarks made in regard to the investigation of the resistance of cancel- 

 lations made with oil inks apply in general to canceling and other inks for use 

 with rubber stamps. 



MATERIALS USED FOR THE MANUFACTURE OF CANCELING AND 

 OTHER STAMPING INKS. 



1. Volatility and Penetrating Power. 



The methods which have been described above will be found useful in de- 

 termining the suitability of liquids for use as bases or constituents of bases of 

 canceling and other stamping inks. 



2. Sedimentation Test. 



A modification of the sedimentation test described may be employed with 

 good results for the purpose of ascertaining the suitability of lampblack and 

 other pigments for use in the manufacture of canceling and other stamping 

 inks. The results, of course, are mainly of value for purposes of comparison. 



The conditions of the test may be modified to suit the purposes of the investi- 

 gation and the character of the materials to be compared. The writer has ob- 

 tained good results in the comparison of lampblacks and other blacks rich in 

 uncombined carbon by the following method, which was so planned that the re- 

 sults might be applied to stamping inks made with either a water-solution base 

 or an oil base : 



Mix 0.5 gram of the black to be tested in a mortar with dilute glycerin (87.5 

 cc of glycerin diluted with water to 1 liter). Rinse the mixture into a 100 cc 

 Nessler cylinder and dilute to the 100 cc mark, using the same dilute glycerin. 

 After having prepared a series of tubes, each containing a portion of one of the 

 blacks to be tested, close each tube with a cork and shake thoroughly each tube 



