We are glad to chronicle, says the New York Independent, the discovery of a chemical process by which the photographing of tank tills, checks, bonds, and certificates can be prevented successfully. The discovery was made by Mr. George Matthews, one of the chemists employed by the Montreal City Bank, who has taken out patents not only in Canada but in the States, The discovery is of a calcined green oxyd of chromium, which produces a green tint, and this being mixed with the black carbon ink, produces an impression which is unalterable. Every possible chemical test has been applied to the erasing of the impression, but not one has been successful, the black impression and the paper itself being destroyed where the green tint is. Professor Henry, of the Smithsonian Institute, B. Silliman, Jr., Dr. Torrey, and other scientific men, have all testified to the perfect security afforded by the "patent green tint and black carbon ink." The newest bank bills, the new issues of treasury notes, the specie certificates employed by the banks in their Montreal exchanges, are all printed in these two permanent inks. The American Bank Note Company now uses it, as it has of late been used by Kawdon, Wright, Hatch &Edson. It is hardly twelve months since the patent was obtained, yet it is rapidly coming into exclusive use for bank note and stock certiticate printing. The red ink which has been so much in use is found no longer available, as it can be photographed without injuring the bill. The green tint and black ink cannot be.photographed without doing so, in all cases and circumstances. The claim is to the use of the calcined green oxyd of chromium for making ink for printing from engraved plates and other objects.