1036
JOURNAL OF CHEMICAL EDUCATION
MAY, 1930
A very fine article covering the various theoretical phases of photogravure etching has been written by H. Mills Cartwright, published in "Proceedings of the Seventh International Congress of Photography," July, 1928, under the title "The Progress of Photogravure Etching."
Inks The drying of an ink takes place by oxidation, evaporation, and penetration into the paper. The paper used in a photogravure process will not permit of any great penetration because of its glazed surface, consequently most of the drying is accomplished by evaporation. To aid in this process alcohol is sometimes added and the printed paper warmed by a heated drying drum. The binder used to keep the pigment or lake on the paper is usually a natural hydrocarbon called ~ilsonite. However, i t is colored too dark to be used in the lighter colored inks, and so resins and gums are substituted. Obviously gritty particles must be absent for if they got in between the plate and the "doctor blade" they might scratch the printing surface. The ink used in most intaglio processes, except rotogravure, must have an oil, which on oxidation can bind the pigment to the paper. This is usually linseed oil, which has been previously treated with catalysts to aid in the oxidation. The ink must dry fast so that i t will not offset on to the next sheet. The coloring matter may be a lake, an earthy pigment, an artificially prepared insoluble colored substance, or eome form of carbon black.
Additional References There is a wealth of very valuable material in these books: H E ~ ~ ~ SATRN UCN K, "Die Kunst des Radierens," Paul Cassirer, Berlin, 1908. E ~ S S.TLUMSDEN,"The Art of Etching," J. P. Lippincott, Phila., 1925. C m n m s W. HACKELMAN, "Commercial Engraving and Printing," Commercial Engraving Publishing Company, Indianapolis, Indiana, second printing. revised. 1924.
Chemical Abstracts Now Covers 1500 Periodicals. According to E. J. Crane, in a recent issue of the News Edition of Industriel and Engineering Chemistry, there are over 1500 periodicals now appearing which publish a t least occasional articles reporting new information of chemical interest. In its efforts to cover the chemical literature of the world completely, Chemical Abstracts is continually seeking to learn of new scientific journals and to unearth obscure ones. The total number systematically examined has just reached the 1500 mark, and experience has shown that there is always another to be found in Japan or Russia or some other distant country and that one or two new ones will put in their appearance before this can be printed. These periodicals have been classfied: (1) by subjects or fields covered, and (2) by countries in which they are published. Tables showing the number and percentage in each class accompany the original article.
