ANALYTICAL CHEMISTRY
1216 electrodes) which was standardized a t frequent intervals with a sodium bicarbonatesodium carbonate buffer solution of pH 10.02a t 25" C. (I). The test solutions were prepared by diluting aliquot portions of 50% carbonatefree sodium hydroxide solution with carbon dioxidefree distilled water until the desired pH values were obtained. The p H values a t 25' C. were 12.38, 12.49, 12.59, and 12.68(all +0.02). The visihlelight transmittance of each dye waa obtained using the recording spectrophotometer with a 1-cm. cell. The solutions were kept under an atmosphere of nitrogen during transfer a6 well as storage to prevent carbon dioxide absorption. The oonoentration of each dye was adjusted to obtain optimum response from the spectrophotometer, and maintained exactly the same in the test solution samples. I n this way the transmittance differences among test solutions containing the same dye were function8 of pH values alone. The concentrations of the dye solutions by volume in the cell were: Acyl Blue 2.2%, Parazo Orange 1.9% Poirricr's Blue 0.37%, sodium indigodisulfonate 0.37% and Tropaeolin-0 1.9%. Poirrier's Blue and sodium indigodisulfonate exhibited the most profound color transmittance changes over the pH range under consideration. In alkaline solution, however, these two dyes fade 80 rapidly that they arc of doubtful practioal value. Acyl Blue showed but slight change in color transmittance over the range under teat, and is, therefore, also of doubtful value.
Tropaeolin-0 and Paraea Orange cxhihit moderate change in color transmittance with p H and show mme promise. As illustrated in Figures 1 and 2, a t wave lengths greater than 490 mp, both dyes exhibit decreasing light transmittance with increasing pH. Below 490 mp, this relationship tends to he reversed. If a suitable filter were used to absorb light below 490 mp in wave length, the light transmittance of B solution containing one of these two dyes as measured by a photoelectric instrument, can t,hen be calibrated to read pH within 8, limit.ed range. This method is extremely sensitive to dye concentration, It is necessary, therefore, t.hat the dyo concentration employed for pH determination of an unknown cormpond exactly to that employed in the pH calibration. ACKNOWLEUGM EN'P
The author wishes to acknowledge the advice and assistance of
B. H. Kindt of the General Electric Sehenectady Works Lzhobocttory. LmERATURE: CITED (1) Rates. R. G., Pinohing, G. D.. and Smith. E. R.. J . R e r m x h Natl. Bur. Standards, 45,429 (1960). Rec~xrv.ofor review X'orornbev l!l, 1!)61.
Accepted A ~ r i l 2 3 1962. ,
Method for Staining Cyclotols, Ednatols, Pentolites, and Picratols for Observation and Study of the Non-TNT Phase FRANK PKISTERA Picatinny Arsenal, Dower, N. J .
r HREE desirable properties of a high explosive are high brir s a n c e (power), low sensitivity, and ability to he cast loaded (melting point helow 100" C.). High explosives like Cyclonite (RDX), Haleite (ethylenedinitramine) and pentaerythritol tetranitrate (PETN) which are very brisant, or ammonium picrate (Explosive D) which is relatively insensitive, are too high melting t o be crtst loaded, whereas TNT, iThich can be cast loaded, is neither very brisant nor very insensitive. Very brisant or vory insensitive high explosives which can be cast loaded can be prepared by casting a slurry of molten T N T with RDX, Haleite, PETN, or Explosive D. Such mixtures are known, respectively, Cyclotols, Ednatols, Pentolites, and Picratols. In the Rolid, a6 well s . 8 in the molten state, such mixtures, referred to as cast binary explosives when solid, consist of a TNT and a non-TKT phase. As the properties of the melt prior t o casting (such as viscosity, homogeneity, pourability, etc.) depend in part on the distribution of the non-TNT phase in theTNT phase, a knowledge of such distribution is desirahle. It was to study such distrihution that this investigation was undertaken. To ohsenre and study the particle size dietribution of the nonT N T phase in the binary casts, i t was considered desirable that a staining method he rwailable whioh would render the particles of the non-TNT phase dearly visible for microscopic study and photomicrography. T N T reacted with sodium hydroxide, potassium hydroxide, ammonium hydroxide, and ammonium sulfide giving a reddish ooloration (1-8). Since these reagents did not give a coloration with the non-TNT phase of the various casts, it wm considered that such resgents might form a basis far a suitable method. RESULTS
Unsuccessful Experiments. The reaction of TNT with sodium hydroxide, potassium hydroxide, ammonium hydroxide, and
ammonium sulfide is generally carried out in an et.hano1 or acetone medium in which TXT is saluhle. In attempts t o use such systems it was found that thr wddiah coloration produced
Figure 1. Cross Sections of Standard Casts 12 X Upper lelf, W/40 C~clotol Upper right, 5U/M Ednalol
Lore. laft, 50150 Penfoliie Lnrer tight, 50/50 Picrvfol
1217
V O L U M E 24, N O . 7. J U L Y 1 9 5 2
ing the reagent, kept a t ambient temperature, t o the rast whioh was cooled with dry ice. In this manner, the reagent, being a t room temperature, reacted with the T N T phase, producing a reddish coloration. The reaction then almost stopped immediately after the reagent became cold by contact with the east, and in addition the mobility of the reagent deoreased markedly after oaoling. Using the above-mentioned system, a method was worked out in detail and applied t o Cyclotols, Ednatols, Pentolites, and Piers, tols. In mch preparations the unstained particles of the nonT N T phase appeared and remained clearly visible indefinitely in the reddish purple TST matrix as long as the cast w&8 kept oooled with dry ice. This allowed the study of the non-TNT phase by observation with a binoculsr microscope and a180 by photomicrography. Photomicrographs of representative binary casta were made, Figures 1 and 2. In them the dark area8 represent the T N T matrix and the white areas the nan-TNT partioles. EXPERIMENTAL PROCEDURE
Figure 2.
Cross Scctiun uf Experimental Cyelutul C a s t s 12 x
Preparation of Cast. A eafit, LL/le inch in diameter and approximately 1 inch in height, was polished using first a paste consisting of 100-mesh emery and water, and then a paste at emery flour and water. The east wa8 washed free of emery with water, air dried, and gently rubbed over once with cotton moistened with acetone. Test Assembly. The test assembly (Figure 3) consisted of an aluminum can, 1 inch in height and 2 inches in diameter, fitted with a cover which had a hole in the center 0.75 inch in diameter. This hole was I / , $ inch larger than the diameter of thr cast which was accommodated in B the oDenins. The can had a hole approximately 0.5 inch
0 I.
rectaneular ooeni&
D E
...
'/a
X 1.25 inches which was s&-
~~~~~~~~~~~~
bvo'adhesive t m e whioh also served to hold the cork disk i n position. Procedure. The poliahed cast was adjusted in the adapter (can), 80 that its polished surface was approxiF mately l/* inch above the cover of the can with the help G of a little molding d a y placed at the bottom of the cast. The L/L6-inehspace around the cast on the rover of t h e a n w s , ~sealed with molding clay. The can was filled with H crushed dry ice added through the side opening which was subsequently taped with adhesive tape, leaving only J about '/,e-inch opening at the lower end to allow the G gaseouscarbon dioxide to escape. Approximately 1 minute after the addition of the dry ice to the can, 3 drops of Figure 3. Test Assembly (1.36 X ) a 1 N potassium hydroxide solution in diethylene glycol were spread on the surface of the cast. The east was A . Class slide F. Adhesive tape covered with a cover slip, and the opening in the cork B . Coverslip G . cast c. Clay R. Carbon dioxide escape opening insulator w*&scovered with a 1 X 1.5 inch glass slide D . Corkinadator J . lnrulrfing felt amd tape using a little adhesive tape to fasten the slide to the sides E . Metal can and cover of the cork. The stained surface of the cast was examined with white reflected light using a binoculsr miroseope (2.0 X objective, 10 X ocular) and photomicrographed by T N T with the reagents 11-ould diffuse and completely mask wing white reflected light. the non-TNT phase. Attempts to eliminate the masking by ACKNOWLEDGMENT blotting the cast immediately after the reddish coloration had developed failed heoause the non-TNT phase did not remain The author is grateful to the Ordnance Corps for permission to clearly defined. The use of ammonium hydroxide applied as a rublish this report and wishes to express his apprecktion to A. J. fine spray to the surface of the cast was also investigated, hut it :]ear, C J. Bain, Robert Frye, C. R. Dutton, and C. W. Clark of proved ineffective in producing 8 colaration in which the non'icetinny Arsenal for help rendered in expediting the preparation T N T phase remained visible and distinct. md puhliration of this report. Successful Experiments. In an effort t o reduoe the masking UTERATURE CITED effect by the diffusion of the reddish coloration, a 1 N potassium 1) Clift, G . D.. and Federoff, B. T., "A Manual for Explosives hydroxide solution in diethylene glycol was tried because this Lsborstories," Vol. I, pp. 11, 12, Philadelphia, Lefsx Society. d u t i o n is very viscous and diffuses very slowly. This reagent 1o*n A"71. when first used at room temperature produced B reddish coloraa) Colver, E. dew. S., "High Eaplolosives," p. 233. New York, tion with the T N T phase in which the non-TNT phase appeared D. Vsn Nostrand Go., 1938. 3) Marshall. A,. "Ex~losives." Vol. 11. D. 730. Philadelphia. very distinct, However, after ahout 30 seconds the reddish colP. B1akistoh.B Sons & Co.,' 1917. oration became darker and the slow diffusion masked the non1?.EOEIV&D for review November 3, 1951. Aooepted Mey 1. 1952. T N T phase. This slow masking was finally eliminated by apply-
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