3 90
T H E JO.URNAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
AS the plastic sheet and mold would naturally weld together in the hot press, various methods are used t o prevent the plate sticking t o the negative mold or cast. A layer of oiled paper, thin metal, talc dust, etc., between t h e mold and cast has proven satisfactory but care must be taken when using paper or foil to see that it is not torn or trouble may result. The use of the foil or paper produces a rounded point'to the half-tone screen and produces a more desirable printing plate than the original zinc etching which generally has a protruding crown or shoulder thereby allowing ink to collect behind the point, soon blurring the plate. The smooth rounded point produced on the phenol plastic by the use of the intermediate paper or metal foil makes a plate which does not gum up and blur with the printing ink. Half-tones have been produced from I 50-mesh screen and 1 5 0 screen is the highest used in ordinary halftone work. The ordinary newspaper cut is produced from screen not exceeding IOO mesh, as the larger dot is required for printing on coarse cheap paper. Any form of line work can be reproduced with accuracy and is in general an easier proposition to handle than the half-tone. Mounted plates may be molded directly upon the block of wood and come from the press blocked and ready for flat bed printing. I n this form the cut cannot be unblocked. The plates are also produced in thin form (1/16 inch thick) and are afterwards in another operation blocked by tacking or gluing like t h e regular zinc cuts. Plates blocked or mounted on wooden blocks by tacking may be readily unblocked. The weight of the molded plate is one-sixth the weight of the corresponding zinc, etchings, and contributes a saving in shipping costs equal t o the original cost of the plate. One square inch of plate weighs l / p oz. Ready for shipping 35 sq. in. weighs 4 oz. I t should be borne in mind in this case t h a t in extensive advertising t h e cost of mailing or expressing the zinc cuts is often equal t o the original cost of the etching. REDMANOL CHEMICAL PRODUCTS COMPANY 636 w. 22ND STREET CHICAGO
THE SETTING OF LITHARGE-GLYCERINE CEMENT' B y H. E. MERWIN Received December 26, 1916
A little litharge which had passed a zoo-mesh screen was spread in a large excess of glycerine on a microscope slide under a cover-glass. After an hour indications of the crystallization of another substance around the surfaces of the litharge grains could be seen; after three hours the new substance was very apparent; and after 2 4 hrs. t h e original grains of litharge were replaced or firmly bound together by interlocking crystalline aggregates of the new substance. These aggregates consisted of radiating fibers. Grains in a similar slide held a t 80" C. for an hour were firmly cemented. The new crystals had similar optical properties in both cases. This cement is very important and not fully appreciated, e. g., it is used in very large quantities in lining the digesters in the manufacture of sulfite~pulp.-EDIToR's NOTE. 1
Vol. 9, No. 4
Glycerine, pure or diluted with j to I O per cent of alcohol or water, heated t o boiling and agitated with litharge, gave similar crystals which were much less closely aggregated. Agitation prevented to a large extent the covering of the litharge grains by the new crystals. In the best sample of material thus preI O per pared-afterwards used for analysis-about cent by volume of unattacked litharge and g o per cent new crystals were estimated microscopically. Analysis showed 70.8 per cent of Pb, which corresponds to 5 per cent residual PbO, and g ; per cent of the compound' C3H602.Pb0,representing the new crystals. The crystals are apparently orthorhombic. The refractive indices are, a = 1.75, /3 = 1.80, y = 1.84, with y parallel t o the length. The crystals had been slightly attacked by the alcohol used in washing them. After standing with glycerine for several days a t ordinary temperatures the centers of the larger grains of litharge t h a t had passed a zoo-mesh sieve were still unattacked. Probably coarser grains would remain indefinitely. GEOPHYSICAL LABORATORY CARNEGIE INSTITUTION OF WASHIIGTON D C. WASHINGTON,
THE USE OF A CONDENSER TO PREVENT ARCING IN BOMB CALORIMETERS B y FREDF. FLANDERS Received January 16, 1917
Commercial lighting current of I I O volts is quite commonly used for igniting the charge in bomb calorimeters. A typical arrangement is t o connect two 32C. P. lamps in series with the fuse wire. Objections have been raised t o the use of current of such high voltage on account of the uncertain amount of heat developed b y the arc formed a t the instant the fuse wire burns out.2 The arc may be entirely obviated by the use of a 2 mf. condenser. This is connected across t h e leads running to the fuse wire and as close to t h e latter as possible. When protected in this manner t h e IIOvolt current produces scarcely a visible spark when t h e current is broken. The use of the condenser might also prove advantageous where a storage battery or other source of low voltage current is used, for even with voltages as low as I O or 1 2 volts there is still an appreciable arc when the current is broken. Condensers satisfactory for the above use may be had of almost any electrical supply house, particularly those dealing in wireless apparatus. They are listed as flat telephone condensers, should be of about z mf. capacity and tested for 500 volts. A very neat one, z X 4 X s/4 inches, was supplied by the Clapp-Eastham Co., of. Cambridge, Mass., for ninety cents. CHEMICAL LABORATORY ON MENTAL DISEASES MASS.COMMISSION 74 FENWOODROAD, BOSTON 1
This compound was prepared by T. Morawski 1.7. prakt. Chcm..
J., 256, 2131 in his original studies of this cement. 2 U. S. Bureau of Standards, Circular 11, p. 7, issue of May 15, 1911. THIS JOURNAL, 9 (1917). 106. Under (6). Firing current.
22 (1880). 401, and Dingier's p d y f e c h .
