ink should be such that the volatile matter will not exceed the above limits when the 

 ink is exposed under the conditions named to a summer temperature of 80 F. and 



upward. 



3. DETERMINATION OF RELATIVE PENETRATING POWER. 



(1) Apparatus. 



(a) Homeopathic shell vials about 8 cm long and 2 to 2.5 cm in diameter. 



(6) Strips of white blotting paper, which for a given series of determinations should 

 be cut from the same sheet and of exactly the same dimensions. A convenient size is 

 12 mm wide and 25 cm long. 



(c) A pair of dividers with arms 15 cm long or longer. 



(d) A millimeter rule. 



(2) Determination. 



Place approximately 5 cc of the ink or other material to be tested in one of the "shell 

 vials" described above, and if several samples are to be tested arrange the vials in a 

 row. Place 5 cc portions of distilled water in each of two of the vials, and put one of 

 the vials containing water at each end of the row of vials containing samples to be 

 tested. Proceeding from left to right, insert a strip of blotting paper in each of the 

 vials, recording the exact time the paper was placed in each vial. The blotting paper 

 should maintain a nearly upright position. The liquids gradually ascend the strips 

 by capillarity; the strips, however, should be in such a position that the liquid does 

 not ascend by capillarity between the edges of the strips and the sides of 

 the vials. 



At the expiration of exactly 15 minutes from the time each strip is inserted in the 

 vial, measure the height to which the liquid has ascended the strip of paper by means 

 of a pair of dividers and record the distance in millimeters. A second set of readings 

 may be taken at the end of 30 minutes or 45 minutes. 



After all of the measurements have been recorded reduce the results to the terms 

 of the penetrating power of distilled water, taking the penetrating power of distilled 

 water as 100. This is accomplished by dividing each result by the average of the 

 results obtained for the distilled water contained in the vials and multiplying the 

 quotient by 100. Ten samples may conveniently be tested at one time by working as 

 above described. The method gives good comparative results, and has been applied 

 not only to canceling and other stamping inks, but to the liquids used for the manu- 

 facture of these inks. 



In observing the penetrating power of a given sample of ink it is important to remem- 

 ber that the value of a canceling or stamping ink depends upon its power to penetrate 

 the paper during the first minute or fraction of a minute following its application to 

 the paper. It is well, however, to keep the tests under observation for several hours, 

 as information can thus be obtained in regard to the extent to which the coloring 

 matter contained in the ink follows the liquid baae of the ink as it passes through the 

 paper. In some cases the coloring matters keep pace with the liquid portions of the 

 ink; in others an uncolored band at the top of the portion of the paper which is wet 

 with the ink shows that the coloring matter does not proceed through the paper as 

 rapidly as the base of the ink. This may or may not be an undesirable result. If the 

 colorless band is due to a difference in the rate of penetration, it is undesirable. If it 

 shows that the dye contained in the ink has an affinity for the fibers of the paper, it is 

 evidence of a valuable quality. 



Additional information can be obtained from the penetration test by removing the 

 strips of paper from the vials, cutting off the part of the paper which has actually been 

 immersed in the ink, and treating the upper part successively with petroleum, ether, 

 alcohol, and other solvents for removal of the constituents of the ink soluble in these 

 liquids. The extent to which the dye or dyes contained in the ink resist the action of 

 [Cir. 12] 



