DISTINGUISHING INDIVIDUAL SOME INTERESTING EXAMPLES OF RHYTHMIC PRECIPITATION QUANTITATIVE FILTER PAPERS CARL E. OTTO University of Maine,
Orono, Maine
PACKAGES of quantitative filter papers bear distinguishing marks, either colored bands or numbers, indicating the texture of the paper enclosed, but students in elementary classes need only a few circles and to save them unnecessary expense the packages are broken in the stockroom. -This separates the paper from the marks and introduces several possibilities of error. Careless stockroom clerks, not realizing the importance of the markings, may hand out the wrong kind, or return surplus circles to the wrong pachge. The student may ask for the wrong type, and the circles given him do not by their appearance awaken a sense of error. The student may obtain two or more kinds of paper a t one time and unintentionally mix them before use. The place for the distinguishing mark is on the paper itself and it can be easily placed there if a color code is used. Aqueous solutions of organic dyes can be streaked along the edgeof the package, thus marking every circle. When folding, the corner of the foldedback section can be located a t this spot and tom off. Even when not thus removed the dye adds no appreciable weight to the ash of the paper. +Two thousand suots were made by two milligrams of dye dissolved in one milliliter of water. Thus, there is an average of one microgram per spot and loss of dye by leaching or its decrease in weight on ashing decreases this. Stability of color to laboratory fumes is important and the dyes tested were subjected to the fumes of boiling 6 N NHlOH and boiling concentrated HCI. The dyes recommended are (1) Water Blue of Heller and Merz for the close-textured paper used for fine-grained precipitates, (2) Nigrosine CPP of Heller and Merz for the loose textured paper used for gelatinous precipitates, (3) Erie Fast Scarlet 4 BAP of National Aniline Company for the intermediate texture now distinguished by a white band, and (4) Auramine OP of National Aniline Company for the fat-free white band paper. Within a few weeks of starting to use this system the author found two students folding the wrong kind of paper for precipitates standing ready in the beakers. Without identification marks on the circles this error could not have been noticed.
THERALD MOELLER University of Illinois, Urbana, Illinois
ALTHOUGHOstwaldl has already reported a spiral arrangement in the rhythmic precipitation of cobaltous hydroxide in gelatin, the examples illustrated seemed sufficiently unusual to merit recording. Each of the samples, of which only the banded structures are shown, was prepared as follows: To 30 ml. of a hot ten per cent gelatin solution in a 17-an. pyrex test tube were added 5 ml. of a M/10 cobaltous nitrate solution. After setting, the gel was then covered with 10 ml. of a M/5 ammonium hydroxide solution. The tubes were stoppered and allowed to stand in the light of the laboratory, the first one being photographed after eight days and the other two after five days. The green bands of cobaltous hydroxide were joined along one side of the tube in each instance, but this linking tendency disappeared as the'bands became more widely separated. While the structures illustrated are not true spirals, they represent a rather interesting type of Liesegang phenomenon. ~OSTWALD, "Zur Theorie der ~ i & ~ a n ~ ' s c h e nRinge." Kolloid-2. (Zsigmondy Festcchrift). 36, 390 (1925).
