Copying Camera -. - Devices with a n Argus
T o the Editor: An apparatus f& copying photographs and drawings on 35-mm. film in making 2" X 2'' lantern slides is described in J. CHEM.EDUC.,16, 308 (1939); also, a device for copying 2" X 2" lantern slides from 3'/aU X 4" slides. The specifications in Figures 1 and 2 of that article are for a Leica camera.. I have since had occasion to construct similar devices for use with an Argus camera, model C; and since the cost of the latter is considerably less than a Leica camera, the following data may be of some senice. The deerice for making 2" X 2" slides from 3'/rn X 4" slides has the same dimensions as for a Leica camera, with the exception that the opening over which the large slide is placed should be 2'/8" X 3'/aV; and the side of the camera box (not the lens) should be eight inches above the emulsion of the slide to be copied. Dimensions for the autofocusing copying deerice are identical with those for the Leica camera with the following exceptions. The lamps should be ten, not fourteen, inches above the copying board. In place of front lenses, three collars are used: '/2-inch and oneinch collars which may be ordered from any Argus dealer ($1.00 each), and a '/,-inch collar which must be made to order. Changes in sizes of masks, and distance between the surface of the picture to be copied and the edge of the Argus camera box (again, not to the lens) are indicated in the following table. Height, d l dnrhrs, of Posilion of lens
Coilor in inches
comno cdgc above m i . r r
sire of mesh in inches
Number of mask
out (In) (Out) In (Out) In
out In
It will be noticed that the dimegsions have been so chosen that mask number 3 may conveniently be used with either the '/z-inch or the inch collar. Also, by painting lines on this same mask to correspond with the size 3" X 4I/zv, it may be used for two sizes of pictures depending upon the "in" or "out" position of the lens. Exposures are of the same order as indicated in the .. . ongmal aruae. By the use of a supple men tar^ front lens (sl.OO) still larger pictures may be copied. For example, with the copying lens attached, and with the front lens to the "out" position, camera elevation 22l/2", a picture 9'/1" X 143/4"is in focus.
With these devices. which cost under thirtv-five dol, ~~~~Iars for materials, including camera, a novice can make his own slides for a few cents apiece. HUHERTN. ALYEA PRINCETON UNIVERSITY
PRINCETON, NEW JERSEY Symbols or Abbreviations?
To the Editor: The letter from C. E. Ronneberg, on page 44 of the January issue, is very interesting. It seems to me that the symbol "gm" is preferable to "g" for the word "gram" because of the prevailing use of "g" for the acceleration due to gravity. I would like to suggest the use of "mM" for "millimole" and "mE" for "milliequivalent." The symbol " N seems to be good for "normal" because the italicization differentiates it from "N," the symbol for "nitrogen." A similar symbol " M is used for "molar." The spelling of "mole" is preferred to "mol" because of the significance of the ending "01" as used in organic nomenclature. The ending "01" should he reserved for the designation of the hydroxyl group. L. P. BIEFELD P ~ D UUNWERS~TY E LAPAYETTE, INDIANA Oblivion?
To the Editor: Your editorial in the January number of the JOURNAL oa CHEMICAL EDUCATION. ceriainly strikes a responsive chord in me. It happens to be one of my favorite themes. In a paper in this JOURNAI, (15, 541 (Nov., 1938)) I suggested the elimination of the arc process for the fixation of nitrogen, the Le Blanc process for the manufacture of soda ash, the idea of nascent elements, the idea that oxygen and oxygen only supports combustion. I would add to these the following topics as nominations for oblivion: hydrogen peroxide, ozone, the Law of Dulong and Petit, valence as ordinarily presented in the early stages of general chemistry, and ionization tables for electrolytes based on conductance. . I also have a suspicion that we have given Dalton a lot of credit for anatomic theory that he does not deserve. I do not think he should be relegated to oblivion, but he ought to he put in his proper place. GRAHAM COOK ALERIGHTCOLLEGE READING, PENNSYLVANIA
