44 TESTING MISCELLANEOUS SUPPLIES. 



further information consult Lunge, Schluttig and Neumann, 6 Mitchell and 

 Hepworth, and Munson. d The chromate logwood inks and the vanadium inks 

 are not permanent. Among the inks examined by Munson no sample with a 

 specific gravity below 1.035 was permanent, and with one exception no sample 

 containing less than 0.60 per cent of iron. The exception, however, was a very 

 permanent ink, in spite of the fact that it contained only 0.32 per cent of iron. 



CANCELING INKS HAVING AN OIL BASE.* 



The following methods have been devised for the purpose of ascertaining 

 the suitability of canceling inks for the use of the Post-Office Department. 

 Many of these methods will be found of assistance in passing upon the quality 

 of stamping inks for miscellaneous uses. 



It is important that the ink used by the Post-Office Department for post- 

 marking i>ossess in the highest possible degree certain properties. The ink, 

 first of all, must produce an indelible cancellation ; that is, it must be relatively 

 indelible as compared with the ink used for printing the postage stamps. The 

 I>ostmark made with the ink must dry quickly in order that the mail matter 

 may be handled immediately without any blurring or smearing of the post- 

 mark. Both this property and the property of indelibility involve the question 

 of the rate at which the ink penetrates or is absorbed by the fiber of the paper. 

 A satisfactory ink does not harden or form a crust on the ink pad on exposure 

 to the air. There must be no deposition of solid matter on the bottom of the 

 vessel in which the ink is stored, and the pigments, on which the indelibility of 

 the ink depends, if insoluble, must not settle out in such a way as to make it 

 possible to pour off from the top of the container a portion of the ink which 

 contains little or none of the insoluble pigment or pigments. The following 

 methods have been found of value for the purpose of ascertaining the quality 

 of a given sample of ink as well as the appropriateness of certain materials 

 used for the manufacture of canceling inks. 



1. Preparation and Care of the Sample. 



Since canceling inks contain more or less insoluble and volatile matter, spe- 

 cial attention must be given to the preparation and care of the sample. It 

 (i i ust be carefully mixed by shaking before each portion is removed for analysis. 

 and the container must be left open no more than is absolutely necessary for 

 the removal of ix>rtions of the ink. 



2. Determination of Matter Volatile at Ordinary Temperatures. 



Place a carefully weighed quantity (between 5 and 5.2 grams) of the ink in 

 a flat-bottomed aluminum dish 102 mm (4 inches) in diameter. Distribute the 

 ink rompl.-tHv over the surface of the bottom of the dish by gently tilting 1h< 

 same. This quantity of ink should be sufficient to completely cover the bottom 

 of the dish. Place the dish on a horizontal shelf or table where air will have 

 free access to it and where it will be screened in such a way that no dust can 

 fall into it. 



ChemiHch-Technische Untersuchungs Methoden, 8: 762-793. 

 6 Die EisengalhiHtinten. 

 c Inks, Composition and Manufacture. 



*Thi Examination of Writing Inks, J. Auier. Chem. Soc., 190G, 28: 512. 

 Th<> work on .-nicelm- inks is a revision of the methods previously issued 

 as Circular 12 of this Bureau. 



