T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
NOV., 1919
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allowed. The accompanying table records the results, and the triangular diagram shows the lines of equal refractive index. These results accord, within the experimental error, in all but a few instances with calculated values in column j, which have been obtained from the formula n = I . 5 4 2 m -k 1 . j 7 2 d $- I. j 8 O t , where m, d , and t are the fractious by weight of mono-, di- and trinitrotoluenes in t h e mixture. Thus, the refractive index of a mixture a t 38-39' is an additive property, and may be expressed by a linear equation. UNIVERSITY O F NORTHCAROLINA CHAPELHILI,, N. C.
SOME PROPERTIES OF COMMERClAL SILICATE OF SODA1 B y JAMES G. VAIL Received M a y 20, 1919
TNT
DNY
suggestive of a method which may be useful when simpler ones fail. The portion of the diagram of most interest is of course the region around the eutectic point, where the boundary curves intersect. We therefore confine the measurements t o those mixtures which freeze below 40 ', the eutectjc temperature being near 17'. Such data when chartered would furnish a key t o the interpretation of data concerning any unknown mixture, for the composition of any unknown would be fixed on a line across the diagram, and then some other measurement might possibly establish the point on t h a t line representing t h e composition of the mixture. COMPOSITION IN WEIGHTPER CENTS
MNT DNT 40 60 45 55 50 50 55 45 40 60 35 60 30 60 25 60 20 60 15 60 60 10 60 5 60 0 60 35 30 60 40 55 55 35 55 30 25 55 20 55 45 50 40 50 50 35 30 50 25 50 20 50 15 50 10 50 50 45 45 45 45 40 45. 35 45 30 45 25 45 20 45 15 40 55 50 40 45 40 40 40
REFRACTIVE INDEX T N T Observ. Calc. 0 1,5599 1,5600 1.5580 1.5585 0 0 1,5568 1,5570 0 1.5557 1,5555 0 1.5539 1.5540 1,5541 1.5544 5 10 1.5548 1 5548 1,5556 1.5552 15 1,5564 1,5556 20 1.5554 1.5560 25 1.5564 1,5564 30 1.5568 1.5568 35 1.5572 1.5572 40 1.5621 1,5619 5 1,5634 1,5638 10 1.5605 1,5606 5 1,5623 1,5625 10 1.5644 1,5644 15 20 1.5664 1.5663 1.5685 1,5682 25 5 1,5585 1,5589 10 1.5602 1.5608 1.5622 1.5627 15 1,5643 1.5646 20 1,5668 1.5665 25 1.5682 1.5684 30 1.5700 1.5703 35 1.5722 40 '1.5725 1,5570 1.5574 5 10 1,5589 1.5593 15 1.5608 1.5612 20 1,5630 1.5631 25 1.5645 1,5650 30 1.5669 1.5669 1.5686 1.5688 35 1.5710 1,5707 40 1.5557 1.5559 5 1,5574 1.5578 10 1.5594 1.5597 15 1.5612 1 .5616 20 I
I
COMPOSITION IN WEIGHTPER
REFRACTIVE INDEX M N T D N T T N T Observ. Calc. 1.5631 35 40 25 ,5635 1,5657 30 40 30 ,5654 1.5678 25 40 35 ,5673 1.5695 40 20 40 ,5692 1.5557 ,5563 10 55 35 1.5577 5582 50 35 15 1.5594 ,5601 20 45 35 1.5614 ,5620 25 40 35 1,5636 ,5639 35 35 30 1.5658 ,5658 35 30 35 1.5675 40 25 35 ,5677 1.5699 20 35 45 ,5696 1.5565 55 30 15 ,5567 1.5583 20 50 30 ,5586 1.5601 ,5605 45 30 25 1.5620 40 30 30 ,5624 1.5638 ,5643 35 30 35 1.5664 ,5662 30 30 40 1,5682 2.5 30 45 ,5681 1.5568 ,5571 55 25 20 1,5585 ,5590 50 25 25 1.5606 ,5609 45 25 30 1.5626 ,5628. 35 40 25 1.5650 .5647 40 35 25 1.5668 30 25 45 ,5668 1.5576 ,5575 25 55 . 20 1,5592 SO 20 30 ,5594 1.5610 ,5613 45 20 35 1.5628 40 20 40 ,5632 1.5656 565 1 35 20 45 1,5579 .5579 55 15 30 1,5596 .5598 50 15 35 1,5622 ,5617 45 15 40 1.5636 ,5636 40 15 45 1.5582 55 10 35 ,5583 1.5597 ,5602 50 10 40 1,5620 45 ,5621 45 10 1,5586 55 5 40 1.5606 50 5 45 ;~~~~ 1.5592 45 .5591 55 0 CENTS
~~
.
The apparatus used was an AbbC refractometer, -through the prisms of which water circulated from a thermostat at 38-390* the temperature coefficient is small, slight temperature variations were
,
Sodium silicate is a name familiar t o every chemist, but a somewhat extended experience and a search of the literature has led t o the observation t h a t the properties of commercial silicate of soda and the wide variety of physical characteristics which can be secured in its different types are often imperfectly understood. New uses for silicate of soda are'continually being found, and i t is thought t h a t a more general knowledge of its properties may be helpful. A definite compound of t h e formula Na&On is easily prepared in crystalline form frum solutions containing sodium hydroxide and commercial sodium silicate. I t crystallizes with 9 molecules of water. I t melts in its water of crystallization a t about 40' C. I t is rapidly decomposed by the carbon dioxide of the air. As f a r as known, this product has no commercial significance, because it lacks those colloidal properties upon which practically all of the commercial applications of silicate of soda depend. All the forms of sodium silicate in commercial use contain more silica than is indicated by the formula NaZSiOa, one grade having about four times this amount. The ratio between sodium oxide, NazO, and silica, S O 2 , may be varied between I t o 4 and 2 t o 3. Products more alkaline than the latter ratio are not made, on account of their tendency t o form crystalline masses, which would interfere with their usefulness; and the practical limit in the other direction, namely, I t o 4, is determined by the very low solubility of fused sodium silicate containing larger proportions of silica. The fused masses resulting from the reaction between pure sand and sodium carbonate, or sulfate, have the physical appearance of glass, but are less permanent, and-especially the more alkaline typeseffloresce in damp air in the course of a few weeks, so as t o become practically opaque. The commercial grades are usually colored either greenish or yellow, due t o the presence of small quantities of ferrous or ferric iron. Ferric iron is more frequently observed in the alkaline types, while those rich in silica usually I Presented before t h e Division of Industrial and Engineering Chemistry a t the Philadelphia Meeting of the American Chemical Society, September 2 to 6 , 1919.
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
appear on the market a s a greenish glass, not unlike window glass or green bottle-glass. The solutions of these different silicates vary largely i n their characteristics. To take the two extremes: t h a t with a ratio of I t o 4, as above, may be concentrated t o about 37' BB., which corresponds t o about 34 per cent total solids. At this concentration its consistency is jelly-like, and masses of i t may be picked up in the hand and shaken off without difficulty. If it is cooled t o 5' C. it may be molded in t h e hand into balls which bounce very much like rubber balls, but which, if subjected t o too much strain, will break with a clear vitreous fracture. The same result may be secured a t ordinary temperatures by slightly increasing the concentration. Any forms molded from such a solution will slowly flatten out if left on a smooth surface, much after the manner of asphalt in warm weather. I n contrast t o this type, a silicate with a ratio of 2 t o 3 is thinly fluid a t 37' BB., and may be concentrated t o approximately 69' BB., or about 62.5 per cent total solids. At this Concentration its consistency is such t h a t one may push a pencil into i t with some difficulty. I t flows slowly. A bubble in a tube of 2 in. in diameter will rise about 4 in. in 24 hrs. a t 20' C. through such a solution. While the siliceous type breaks like a jelly, this type is very tough and may be drawn into long threads or "pulled" like molasses taffy until i t becomes opaque and white. It is extremely sticky and dries much more slowly than the less alkaline forms. It will absorb moisture in damp weather. Between these two extremes any intermediate grade can be produced; thus a considerable range of characteristics which are of importance in the adhesive uses of silicate of soda can be secured. As the proportion of alkali increases, the possible concentration increases, and there are in regular use different silicate solutions of 3 7 ' , 40°, 42', 47', jo', 5 2 ' , 60°, and 69', each adapted especially for some commercial use. Silicate is usually placed upon the market a t a concentration near the practical limit, t o avoid the expense of shipping unnecessary amounts of water. It is mostly sold in solution, however, on account of the difficult solubility of the anhydrous material. The colloidal nature of silicate solutions is indicated by boiling points but little higher t h a n the boiling point of water. This is true even in the case of the 69' solution which contains more t h a n 62 per cent of solids. The freezing points also are but slightly depressed from t h a t of water. The ordinary 40' silicate freezes a t about -3' C. I t becomes opaque and white. The freezing process is characterized by the rapid growth of long crystalline masses, which contain more water t h a n the 40' solution. When such a solution is slightly warmed, the crystals tend t o float, and it often happens t h a t tank cars of 40' sodium silicate which have frozen and then thawed will contain a highly concentrated silicate a t t h e bottom and a relatively dilute solution at the top. These are readily mixed together, and t h e solution thus secured i?, as far as known, identical in properties with
Vol.
11,
No.
II
the original. Solutions above 60" BC. in concentration do not lose their transparency on freezing, but become progressively harder and finally brittle. They show no tendency t o separate into concentrated and dilute portions when warmed t o ordinary temperature. Silicate of s6da is precipitated by most salts of t h e heavy metals; and the precipitates are believed t o contain free silicic acid along with metallic silicates. Precipitation is also effected by various liquids which tend t o dehydrate the silicate solution. For instance, alcohol, glycerin, salt brine, and strong ammonia solutions will precipitate concentrated solutions of sodium silicate. Such precipitates may be redissolved, but the second solution has somewhat different characteristics from the original silicate solution, notably in respect t o viscosity. An exact study of the nature of these precipitations would be a n interesting field for research. The viscosities of solutions of silicate of soda are of interest in connection with many of its uses. The forms rich in silica rise slowly in viscosity until t h e condition of jelly is approached, when they rise very sharply. This is true whether the rise in viscosity is due t o decrease of alkalinity, decrease of temperature, or increase in concentration. T o prepare a silicate adapted as a quick-setting adhesive, use is made of this fact. A change from a liquid t o a solid condition may occur with t h e loss of as little a s I O per cent of moisture, this amount being very quickly absorbed into a layer of paper board when the silicate is thinly spread on its surface. Solutions adaptable for this sort of work do not air-dry below about 2 0 per cent moisture. If dried in mass t o this condition, the solid solution has the appearance of glass, becomes hard enough t o cut the hand, and is much more soluble t h a n anhydrous silicate of the same relative composition. If suddenly exposed t o a temperature above the boiling point of water, such a solution will expand into a mass of permanent bubbles of beautiful white appearance and apparent specific gravity as low as 0.01. Such a product is an excellent thermal insulator. Silicate of soda is the most convenient source of gels of silicic acid which may be prepared with either alkaline or acid reaction b y neutralizing more or less completely. Any mineral acid can be used for this purpose, and by varying concentrations of acid and of silicate solution, gels of a wide variety of physical characteristics can be secured. Strongly acid gels have been used t o prevent the splashink of acid from storage batteries. Very hard neutral gels have been used for preparing material suitable for the adsorption of gases. The strength of adhesives and cements produced from silicate of soda is very great. If pieces of hard wood are glued together, end t o end, with a silicate solution containing slightly more than 3 molecules of silica (SiOz) for each of sodium oxide (NazO), a tensile strength of 500 Ibs. per sq. in. may be consistently secured. About 2 0 0 lbs. per sq. in. tensile strength is required t o pull the fiber sidewise from
Nov., 1919
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
gum veneer, such as is ordinarily used in packing boxes, while 5 0 lbs. per sq. in. is sufficient t o pull the fiber from any of t h e kinds of paper usually used for making built-up board for shipping containers and wall-board. The tensile strength of silicate of soda mixtures used for acid-proof cements is easily brought u p t o 1700 lbs. per sq. in. for air-dried briquettes, while the bond produced by baking silicate of soda and clay, as is t h e practice in the manufacture of abrasive wheels, easily yields a strength above 2,000 lbs. per sq. in. T o recount all t h e uses of silicate of soda and the properties on which they are based is beyond the scope of this article, but in spite of its diverse applications in t h e arts a t this tine i t is plain t o those who have worked with it t h a t much remains t o be learned. Studies are in progress which it is hoped may be useful.
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CHEMICAL DEPARTMENT PHILAI>ELPHIA QUARTZ COMPANY PHILADELPHIA, P A .
PHTHALIC ANHYDRIDE.
I-INTRODUCTION
By H. D. GIBBS Received August 19, 1919
Early in the year 1916 my attention was directed to the shortage of phthalic anhydride and its derivativesl and the difficulty attending the manufacture of this valuable intermediate for certain dyes and medicinals by t h e known processes. The best known and most economical process consisted in the oxidation of naphthalene by means of sulfuric acid in the presence of mercury compounds as catalyst.2 An extensive study of this process on a laboratory scale was very disheartening and my experience in this regard was borne out by t h a t of many other investigators. The yields were very erratic for unknown reasons, occasionally reaching 55 per cent of the theoretical, but averaging nearer 2 5 per cent. This line of investigation was discarded very early and experiments on the vapor phase oxidation of naphthalene in the presence of catalysts were begun with a view t o paralleling a similar process for t h e production of benzaldehyde by t h e air oxidation of toluene. The shortage of the supply of benzaldehyde for commercial uses had resulted in requests upon the Bureau of Chemistry for information concerning the best methods of manufacture and led t o studies on ,~ this process is gent h e chlorination of t o l ~ e n esince erally regarded as the first step in the large-scale pro1 At this time very little phthalic anhydride or phthalic acid rras made in this country and the little that was made was produced a t great expense by t h e use of sulfurlc acid as an oxidizing agent for naphthalene. Consequently there arose a shortage of phthallc anhydride derivatives and the prices were very high. The abnormal prices were about as follo-s Phthalic anhydride, $7.50, and small lots a t $14 per lb , phenolphthalein, $8 t o $20; rhodamine Bx, $75; eosine, $12 t o $15; erythrosine, $24, and purified for food color 530, rose bengale, $50. In 1917 (the Tariff Commission, Census of Dyes and Coal-Tar Chemicals 1917) small quantities of rhodamine B, uranine, phloxine P, and rose bengale B weie manufactured and average prices for the following are reported: Phthalic anhydride, $4.23 per lb.; phenolphthalein, $9 65, eosine, $8.58, and erythrosine, $11.31. Levinstein, J . Soc. DYeYs Colouists, [61 17 (1901), 138, “Uber Indlgodarstellung,” Chem.-Ztg., 32 (1908), 602. 8 Gibbs and Geiger, U. S. Pat. 1,246,739 (1917).
103r
duction of benzaldehyde and some other valuable compounds. This laboratory was engaged in studies on malachite green and was therefore interested in the production of benzaldehyde. Very shortly afterwards I was impressed by the advantage of a direct oxidation process, if such could be devised, eliminating several troublesome steps in the introduction of the oxygen in the side chain of toluene. Many methods have been proposed for oxidizing the methyl group of toluene in the wet way with solutions of various oxidizing substances, b u t these were not studied, being discarded in favor of vapor phase studies. Mixtures of oxygen and toluene, and later atmospheric air and toluene, were passed into contact with various substances a t temperatures varying from the boiling point of toluene t o 5 5 0 ~ . Every substance tested by this method, and they were very numerous, catalyzed the reaction more or less, the valuable products being benzaldehyde and benzoic acid, the former predominating. Ultraviolet light was without effect. The oxides of the metals1 of the fifth and sixth groups of t h e periodic system were found t o be most efficient, vanadium first and molybdenum second. I first gave a summary of this work at t h e Fifty-third Meeting of t h e AMERICAN CHEMICAL SOCIETYin New York, before the Division of Industrial Chemists and Chemical Engineers, September z 7 , 1916. A further account of the work was read a t the Kansas City Meeting in April 1917. Studies of the remarkable properties of the compounds of molybdenum and vanadium, both in a pure state and mixed with various other ingredients, in their power to catalyze other oxidation reactions were prosecuted and the next success was in producing phthalic anhydride from naphthalene. The principal reactions t h a t have been developed are: naphthalene t o phthalic anhydride,2 anthracene t o a n t h r a q ~ i n o n e ,phenanthrene ~ t o phenanthraquinone.4 Others are under investigation. Methods for purification of phthalic anhydride have also been studied.6 The demand for phthalic anhydride being most acute, the naphthalene oxidation was the first t h a t was carefully investigated, t o determine the best conditions of temperature, gas mixture, time of contact, and condition of catalyst to produce the optimum yield. The best laboratory experiments gave a conversion equivalent t o 8 2 per cent of t h e theoretical yield or about 95 g. of phthalic anhydride for each I O O g. of naphthalene. A small-scale factory unit was constructed in t h e laboratory and operated for one hour with the production of about 1 5 0 g. of phthalic anhydride. The operation was then discontinued because of evident defects in t h e construction. The Department of Agriculture issued an announcement6 on June 16, ~ 9 1 7 ,offering cooperation with 1
Gibbs, U. S. Pat. 1,284,887 (1918); application filed September 22,
1916. Gibbs and Conover, U. S. Pat. 1,284,888 (1918) and 1,285,117 (1918). U.S. Pat. 1,303,168 (1919). Lewis and Gibbs, U. S. Pat. 1,288,431 (1918). Conover and Gibbs, U. S. Pat. 1,301,388 (1919). THISJOURNAL, 9 (19171, 815; 022,Paint and Dyug Reporlev, June 25, 1917, p. 16. 2
a Conover and Gibbs,
’
