October, 1927
INDUSTRIAL A N D EiVGI,VEERING CHEMISTRY
color of the seed arils was higher in the treated samples, however. The experiment has not been repeated. AVOCADOS-Immature avocados of the Challenge, Blakeman, Solano, and Colorado varieties were treated with ethylene in a concentration of 1 to 500 a t 35” C. for 5 days. The treatment resulted in an unnatural brassy color of the skin and a decidedly undesirable darkening of the flesh, The fruits were immature. Untreated samples held a t room temperature in paper bags shriveled badly but showed little discoloration of the pulp and none of the brassy tint on the skin.
1139
Summary
The work at this laboratory indicates that there is no change in the composition of the edible portion of citrus fruits brought method Of about by the meager to permit conclusions to The data On dates are be d r a m , but they do not suggest any changes that would not be caused by heat The astringency Of persimmons is destroyed by ~~f3atment.The coloring of persimmons as well as of other fruits is accelerated by its use.
Plastic Magnesia Cements‘ By Leroy C. Stewart MAGNESIUM OXYCHLORIDE RESEARCH LABORATORY, T H E Dow CHEMICAL COMPANY, MIDLAND. MICH.
IXTY years ago Sore12 published the first account of the reaction between magnesium chloride and magnesium oxide which results in a hard, dense, and strong product. He was impressed with the possibilities which the material presented for binding inert aggregate and fillers together, and accordingly applied for patents on what he called “magnesium oxychloride cements.” He did not offer any chemical formula for the products of the chemical reaction, but soon after Bender3 proposed the formula MgC12.5MgO. 14HzO as representing the composition of the cementing material. Other investigators began to study the reaction and offered widely differing formulas, in which the ratio of magnesium chloride to magnesium oxide varied from 1 to 1 to as much as 1 to 10 molecules. KO doubt the difference in conditions under which many of the investigations were performed accounted for the difference in results. Finally, Robinson and Waggaman, studying the reaction between magnesium oxide and magnesium chloride solutions from a physical-chemical standpoint, reported that from solutions of the chloride between 18’ and 35” BB. (sp. gr. 1.141 to 1.321) the same oxychloride is always formed and that its formula is 3Mg0.MgC12.10HzO. Still more recently, Maeda and Yamanes have substantially checked this formula except for the amount of water present. They report a formula of 3Mg0.MgC12.12H20. Even though some such definite oxychloride crystals are formed, in all probability the final result of the reaction in any of the cement products is actually a solid solution in which magnesium chloride, oxide, and hydroxide all exist in addition to the crystals described above.
S
Raw Materials and Their Properties
MAGNESITE-The most common present-day source of magnesium oxide for these cements is the rock commonly called magnesite, which is magnesium carbonate in its natural state, contaminated with more or less silica, lime, and iron and aluminum oxides. Deposits of magnesite are found in many parts of the world. The most important from the commercial standpoint are those located in California and Washington in this country, and India, Greece, and Austria. It has often been proposed to utilize the many large deposits of dolomite (combined magnesium and cal1 2
3 4
5
Received August 12, 1927. Cornpi rend., 66, 102 (1867). Ber., 5, 932 (1871); .4nn.,1159,341 (1871). J. Phys. Chem., lS, 673 (1909); C. A , 4 , 723 (1910). Sct. Paaers Ins1 P h j s . Chcm. Research ( T o k > o ) ,4, 85 111926).
cium carbonates in natural state) for production of magnesia, and many patents have been issued on the subject. It is also feasible to obtain the oxide by calcining the hydrate or carbonate which has been precipitated from other magnesium salt solutions. A purer oxide may be obtained in this way than can be had from practically all natural magnesite rock. In preparing the magnesite for use, the first step is calcination, which removes the carbon dioxide from the magnesium carbonate. This process is carried on in shaft or rotary kilns. The burning conditions are accurately controlled, since the physical properties of the cements made from the oxide are dependent on the correct calcining conditions. If magnesite is heated to higher temperatures and for longer periods of time than are required to produce a material suitable for use in magnesia cements, it approaches a “dead burned” condition, which is the type of product employed in the form of blocks and bricks for many furnace and kiln linings. As used in the Sore1 reaction the oxide is in the condition known as caustic or plastic calcined magnesia. This term gives rise to the name “plastic magnesia cements,” which is often used instead of the longer description “magnesium oxychloride cements.” Before the plastic magnesia can be used in stucco, flooring, or other cement products, it must be very finely ground; in a good commercial product 75 per cent or more will pass a 200-mesh sieve. MAGNESIUMCHLORIDE-Magnesium chloride, the other active ingredient of these cements, is obtained from the natural brines pumped out of the ground in Michigan, from bitterns in California, and as a by-product from the Stassfurt potash deposits in Germany. Originally, magnesium chloride was placed on the market in the solid form in large drums and cash. At present the domestic product is marketed in flake and powder form, the former being obtainable in 100-pound waterproof bags. Chemical Tests
Chemical analysis is all that is necessary to determine the suitability of magnesium chloride for use in oxychloride cements. For the magnesia, however, just as with Portland cement, physical tests of a mixture containing some of the material in question are necessary to determine its acceptability for use. Chemical analyses of commercial magnesium chloride such as used in stucco and flooring are given in Table I, and those of commercial plastic magnesia from several sources in Table 11.
PiBurc I-Maenesia Cement P s i i i f i n ~in Circuit Covrf Reom of County Couffhowe, Midland, Mich.
One of the most iniportarrt iterria of tlie chemical aualysis uf nragncsia is the conrbiiierl m d adsorbed moisturc, which
is determined by subtractirig carbon dioxide content from ignition loss. The quantity is indicative of tlie aging or exposure to inoistore to which the magnesia n u y have heen suhjccted. \\hen the xater of 1rydr:itc exiwxls 5 per cent, tho strengt,lr and setting time of the ccirienting mixture, in which tlie magnesia is used, are likely to be affected. Also high hydrate content is iisunlly accoinpsnicd by atiiiorrnal shrinkage during hardening. Free litiie and calciuili coiiipounds, prol.)ably silicates, which react, with magnesium chloride sollition to form r:iIciiirn cliloride, are detrimental to plastic magnesia.6 For this reason it is always ad ble t o ileterrninc the lime wliich is soluble in a dilute soluhiim o i niagireaiuni chloride. The difficulties arising fruin smnll, but iievcrtlieloia detriineutal, arnourits of lime can be elinrinated by adding to the ccment mixture tlie tlieoretical ainouiit of inagiiesiurn suliate equiralent l o tile h e . 'rahie i~-Chenlicai ~ n i l i y s eof ~ 'rypicvi ~
Ohloridos (Pigures i n *ex cent) Miehixrn
~
,
~ ~ ~l g nme ~ ~i u m ~
California
Geirnnov
'table I J -Chemical Analyses of T y p l d Samples of Commercial Plarlic MaCneSin
6,55
i . 37 1.00 2.61 83.40
0.81 0.08
U.87
6 O!)
4.87
6.64 0.25
2.06 0.5'1
1.54 87.12
1.68 90.21
1.10
0.24 1 .5'%
0.27
0.U!J U.06
5 68
4.46 4.21 711.!10 81.01 1 i x r c c n ~miuiioii ui hlgi'ir.tiiIr0 wbeti d i s k e n i 4
7fJ,!I3
n
1.iine rolubie
iji
IiOliiS.
6 C;iictiialed.
Physics1 Testing
1'li.ysical testing of mngncsia ceirrcnts usually includes determiitation of st,rcngth: time of set, and volume clmnge. As these ecnients are usually used in rckitively thin layers, n test of flat bars 0.5 inch (13 cm.) thick arid 2 inches (5 cm.) wide i s frequently employed to determino t,rarrsverse strength. The standard briquet, such a.3 used in I'ortisnd scalui>. iiili, eoil Stewart, Chcm. Ma. E n x . , 26. 270 (l!P21i.
~
i
~
i
October, 1927
ILVDUSTRIAL A N D ENGINEERISG CHEMISTRY
ticularly adaptable for casting because they have a slight tendency to expand in the molds during setting, thereby accurately reproducing even the finest lines of the mold. A very fire-resistant paint to be applied over wood surfaces
1143
may be made with oxychloride cement as the binder. Closely allied to such a paint in composition is the “Plastic Mosaic” used by Paul Honor6 in the mural painting in the court room of the Midland County Courthouse. (Figure 1)
Absorption of Nitrogen Oxides in an Aqueous Suspension of Phosphate Rock’” By V. N. Morris FIXEDh-ITROGEN RESEARCHLABORATORY, BUREAUOF CHEMISTRY
AND SOILS, W A S H I N G T O N ,
D.
c.
A comparison has been made of the absorption of OSCURRESTLY with involves the formation of calnitrogen oxides with and without phosphate rock the d e v e 1o p m e n t of cium sulfate, which generally present, not only with water as the original absorbent, the ammonia synthesis remains as a diluerit of the but with various solutions of nitric acid as well. This industry it is essential that resulting product. With hyprocedure seemed desirable since in the ordinary there be developed a diversifidrochloric acid d i c a l c i u m method of absorbing nitrogen oxides the concentration cation in products providing phosphate can be obtained.6 of nitric acid in the absorbing medium becomes prothe various forms of nitrogen I t appears entirely logical to gressively greater as the absorption proceeds and prodemanded by the fertilizer apply nitric acid to this use, gressively reduces the rate of absorption. industry and a larger number effecting in one operation the After it had been established that the addition of the of channels through which the neutralization of that acid proper quantity of finely ground phosphate rock tends products can reach their logand the liberation of monoto increase the absorption, the investigation was exical market. Although amc a l c i u m phosphate. The tended to include a study of the absorption in solumonium sulfate constitutes direct absorption of nitrogen tions of the various individual components which might one of the most popular and oxides in phosphate rock, be expected to be present in the mixture resulting from u s e f u l ammoniates now in eliminating the intermediate the action of nitric acid on phosphate rock. As a final use in the American fertilizer formation of concentrated, step undertaken to gain information about the possible industry, liberal supplies are aqueous nitric acid, appears applicability of a countercurrent system, the degree already available from exista desirable simplification of of absorption and the solvent action on the rock in a ing sources. It is desirable this proposal. Some results three-tower system were determined. t h a t p r o d u c t s yielded by obtained in a study of the t h e ammonia synthesis inreactions involved are predustry be complementary rather than competitive. Ameri- sented in this preliminary paper. can production of nitrates is still small and our dependMaterials ence on foreign sources continues unmodified, although nitrates still enjoy unimpaired popularity among fert,ilizer The phosphate rock was Florida pebble rock ground to compounds and in many applications are regarded as necpass a 100-mesh screen completely and a 200-mesh screen essary. Although the technology of the oxidation of ammonia to the extent of about 70 per cent. Different samples varied t o nitric acid is well u n d e r ~ t o o d ,considerations ~ involving slightly in composition, the average PZOScontent being about national defense demand increased peace-time production 32.5 per cent. of t,his war-time essential. Desirable diversification in Both liquid nitrogen tetroxide and gaseous nitric oxide products is obtainable t’hroughthe manufact’ureof ammonium chloride, sulfate, and phosphate and urea, and the oxidation served as original sources of the nitrogen oxides. The former of a portion of t,he ammonia synthesized to form ammonium, was prepared by the catalytic oxidation of ammonia, and the latter by the interaction of sulfuric acid and sodium calcium, potassium, and sodium nitrate^.^,^ Pending the further cheapening of pyrolytic methods nitrite.’ The average purity of the nitric oxide as indicated of producing phosphoric acid, the acceptable method of by the ferrous chloride method* was 97.5 per cent. ,Is rendering available the phosphoric acid of phosphate rock time was available for a nearly complete oxidation of the will doubtless continue to depend on acid treatments. Sul- nitric oxide when this gas was used, the gaseous mixture furic acid is the reagent commonly employed, but its use entering the absorption vessel consisted largely of Kz04, NO*,X2, and 02, regardless of the original source of the Received March 16, 1927. Presented before t h e Division of I n nitrogen compounds. dustrial and Engineering Chemistry a t t h e 73rd Meeting of t h e American
C
Chemical Society, Richmond, Va., April 11 t o 16, 1927. The h-orwegians had in operation a t one time a process, patented by Bretteville (German Patent 217,309), for t h e production of a fertilizer mixture containing “nitrate” nitrogen a n d soluble phosphate, in which crude phosphorite was decomposed by 60 per cent nitric acid. Peacock [U. S P a t e n t 1,057,876 (191311 has proposed t h e direct production of calcium nitrate a n d water-insoluble dicalcium phosphate by exposing a thin paste consisting of ground phosphate rock and wdter t o t h e nitrous gases from an electric arc-a suggested reaction which we have not been able t o verify. A recent patent granted t o Italian interests [Toniolo, British Patent 247,230 (1925); Chem. Age ( L o n d o n ) , 14, 386 (1926)l covers a process f o r absorbing nitrogen oxides in a suspension of insoluble calcium phosphate. 3 Parsons. THISJ O U R N A L , 19, 789 (1927). Ross, Mehring, find -Merz, I b i d . , 19, 211 (1927). 5 Morris, I b i d . , 19, 912 (1927).
Experimental Method and Apparatus
The apparatui was modified several times during the various experiments. Figure 1 shows the arrangement when the source of the nitrogen oxides was liquid SzO1 and the absorption system corisisted of three vessels in series. With flowmeter B calibrated to deliver a definite flow of air, another stream of air was passed through flowmeter B‘, the cooling coil C, arid then saturated with S201a t 0 ” C. 6
F o x and Whittaker, T H I SJOIJRNAI., 19, 349 (1927) Chem Soc , 47, 2170 (1925). Morris, I b r d , 49, 979 (1927).
’ Noyes, J . .4m 8
