662
INDUSTRIAL AND ENGINEERING CHEMISTRY
from the sale of such chemicals as caustic soda, hydrochloric acid, sodium hypochlorite, bleaching powder, chlorides, liquid chlorine, and synthetic ammonia, both anhydrous and in solution, made from by-product hydrogen gas. This shows the elasticity of the gas chlorination process; the pulp and paper factory may or may not enter the chemical market and, if it chooses, can do so on a very profitable basis. The plant of the South African Pulp and Paper Industries, Ltd., a t Springs, pear Johannesburg, Transvaal, began operations in December, 1938 (6, 8). There are both straw pulp and pine pulp units; both are producing bleached or unbleached chemical pulp as well as semichemical pulp. The caustic soda, in concentration of 3 to 4 per cent of sodium hydroxide, is used to cook pine wood under slight pressure; and the black liquor obtained, containing about 1.5 per cent of sodium hydroxide, is utilized for cooking straw in continuous digestion towers under atmospheric pressure. The plant, located near three large gold mines, will supply the water pumped from their shafts, which sink as low as 6000 feet. (The Johannesburg Rand is on a high plateau about 6000 feet above sea level.) The black liquors and some waste are discharged into the “dumps” (milled and exhausted aurific rocks on the surface). The black liquors are mixed with the cake of exhausted ore coming from huge Oliver filters in order to dilute them, and the mud is pumped to the top of the mine dumps. Solar evaporation quickly dries the mud. Thousands of tons of exhausted ore are dumped every day by each of these three mines.
VOL. 31, NO. 6
In January, 1938, La Cellulose du Pin started producing kraft pulp from p i n des Landes a t a plant near Bordeaux, France, and has erected a chlorination section in order to delignify and bleach about 24 tons of pulp per day with chlorine gas; a cheap and strong bleached pine cellulose is thus obtained which brings a good price. In October, 1938, the Cellulosa Cloro-Soda a t Naples started operations in its esparto pulp plant with a capacity of 24 tons per day. The chlorine process now contributes largely to the Italian Government’s policy of self-sufficiency. Up to a few years ago all the cellulose used was imported into Italy, but in a few years none will have to be brought in.
Literature Cited (1) Chimie & Industrie, 18 (Oct., 1927). (2) DorBe, Charles, “Methods of Cellulose Chemistrv”. 19.73. ---(3) Dupont, G., and Fayard, J. de, Chimie & Indust&, 31,No. 4 bis, 784-7 (1934); BUZZ.SOC. chim., 28,175 (1877). (4)Electrochem. Soc., miscellaneous notes. ( 5 ) Fremy and Urbain, BUZZ. SOC. chim., 37,409 (1882). (6) Grove, J. E., South A f r i c a n Printer & Stationer, 18, 227 (1938). (7) Hall, GGsta, “Some Aspects of Modern Pulp Manufacture”, Paper Makers Association of Great Britain and Ireland, 1937. (8) Paper Trade Rev., Technical Convention No., March, 1938. (9) Pomilio, Umberto, IND.ENG.CHEM.,News Ed., 15,73 (1937). (10) Pomilio, Umberto, “Use of Chlorine Gas in Industrial Pulp Manufacture”, lecture, London, 1938. (11) Wenzl, Hermann, “Zellstofferzeugund mit Hilfe von Chlor”. P . 73, 1927. (12) Wingfield, Baker, Whittemore, E. R., Overman, C. B., Sweeney, 0. R., and Acree, S. F., Natl. Bur. Standards, Misc. Pub. M124 (1936). r
Limitations of Tin as a Packing Material
ALLOTROPIC TRANSFORMATION
A. C. HANSON AND G. 0. INMAN Rock Island Arsenal Laboratory, Rock Island, Ill.
T
IN has been found very satisfactory as a packing material for use in ordnance mat6riel. In certain instances rubber cannot be employed, and a material must be utilized which at least simulates some of its desirable properties. Tin possesses softness and plasticity so that it does not scratch steel but deforms readily under pressure to make a tight seal against the cylinder wall. In addition, it will not gall and is easily formed. Tin exists in its ordinary or white form above 18” 0. (64” I?.). Below this temperature the gray variety is stable. The transformation, however, takes place with considerable slowness, except at very low temperatures. The rate increases as the temperature decreases until a maximum rate is reached a t -50” C. The change, although slow in starting at 18”C., may be facilitated by contact with the stable form. Gray tin is a friable substance; when the change to this form has once started, as indicated by a number of warty masses on the bright surface of the white tin, their number and size continue to grow until the whole of the white tin has passed into a gray powder. This transformation has been called the “tin plague.”
That the conversion of white tin to the gray modification cannot be accomplished a t will merely by cooling the specimen below the transformation point, is a known fact. Mason and Forgeng (2) found a temperature of -40” C., as recommended by Cohen and Van Eijk (I), to be ineffective over a period of 6 months on single crystals of tin. They found that tin from the same source as that used for the single crystals when cast in a cold mold transformed readily in less than 24 hours. Further investigation lead them to the conclusion that the presence of as little as 0.0035 per cent bismuth in tin, in an annealed and homogeneous solid solution, can prevent the transformation; but if the same piece is chill-cast, the transformation can proceed uninhibited along the practically pure tin in the interior of the cored crystals which exist in the chill-cast specimen. Tammann and Dreyer (3) consider bismuth the most effective of common metals in inhibiting the transformation. They found 0.1 per cent bismuth necessary for more or less complete protection against transformation to gray tin. In an effort to determine the amount of time necessary t o induce the transformation of white tin to gray tin, without initial inoculation, the writers made several attempts which are summarized in the table which follows.
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663
Allotropic transformation will take place in both annealed and chill-cast commercia1 tin. Although slow in starting, it progresses rapidly at ordinary winter temperatures. Asmall amount of such transformation on the bearing surface of a tin packing would cause leakage. Since a perfect seal must be maintained at ail times in hydropneumatic mechanisms, the relative ease of transformation precludes the use of pure tin as a packing substance in ordnance matkriel. Tests of 0.1 and 0.5 per cent bismuth in tin indicate that even these small amounts of bismuth will increase the hardness and decrease the elasticity LO a marked degree. Since softness and plasticity are the desirable properties for packings, the addition of bismuth would defeat the purpose for which the packing is intended.
0.25 round 0.312round 0 . 2 5 round 0.312round 0.006 sheot 0.006 sheet 0.000sheet 0.006 *beet 0 . 2 6 round 0.312round 0.006 d i e e l 0.0625 sheet
-45
-35 -25
-18 -45
-35 -25 -18
+5 +5 1 6
+5
8 dam 3 days 3 daya 3 days
3 days 3 days 3 days 3 days 8 mo. $ ma. 8 mo.
2 ma.
0 Thie a ~ m p l ewa8 partially submersed i n an electrolyte o f smmanivm stannous ohloride.
After the failwe to produce a change to gray tin in this short time except by immersion in ammonium stannous chloride solution, other samples were prepared for further testa. Two grades .of tin were used. One was a commercialgrade and the other was Bureau of Standards sample 42B prepared for melting point determinations. Chill-cast and annealed samples of each were repared. They were placed in a container suspended in the %,ne tank of an ice manufacturing plant for one year. The temperature of this brine was approximately -10' C. At the end of this time, there were a few dark x ots on one or two pieces which were assumed to be grey tin. s", of the a m pies were =raped smooth and clean, and a small amount of the gray powder from the partially transformed pieces was scraped .onto these clean surfaces. Scratches were made on the surface and the gray powder rubbed into the scratches. The pieces of tin were then sealed in individual glass tubes (Pipure 1) to prevent contamination. The samples were returned to tho brine tank and left there for 4 months. They were then placed on an ,outdoor exposure rack for an additional 6-month exposure to winter weather. The following ssmples were used: NO.
1
2 3 4 6 G
Type of Tin Commeroial
Condition AnnesIed Cbill-csst
Anneded
B. of S. 42B
Annealed
Chill-o-t Annesled
Dimemiom of Sheet, Inch 0.W8
0.070
o.mo
0.008 0.070 0.070
At the end of the winter when they were again examined, transformation had taken place on all the specimens. The .greatest amount had occurred on sample 1. Figure 2 shows that in spots the transformation had proceeded entirely
through the sheet which is approximately 0.008 inch thick. One of the larger areas where the transformation had progressed through the tin is shown at the point marked by the arrow. Slight transformation had also taken place on the inoculated surfaces of samples 2 to 6 , which proved that the gray powder initially obtained was gray tin.
Since some transformationwas found on all samples, it was assumed that bismuth was absent. A color reaction test with a cinchonine-potassium iodide solution indicated the absence oi bismuth in all samples. This finding was confirmed by spectrographic analysis.
Literature Cited
Peeaelrr~o at the 96th Meeting of the Ameriosn Chemical Saaiaty. Milwaukee. Wia. Released for publiapition by tho Chief of Ordnance. U. 8 . Army. Statements and opinions .%re t o be understood m individual ex. pmsione of the authors and not those of the Ordnanoe Dwsrtmcnt.
