WHAT’S NEW IN
PHOSPHORUS D.H. KILLEFFER 60 East 42nd Street, New York, N. Y.
pends upon their content of the element, that element is now being recovered a t the mine and shipped to the point of use in its most concentrated, pure form. Implications of this method of handling the problem are primarily economic and affect phosphoric acid and the high-grade phosphates. What may be its effects on other phosphorus compounds and on fertilizers cannot yet be clearly foreseen. However, tracing the changes now in progress may supply some basis for informed guesses as to the future.
Supply and Demand PLANT OF THE OLDBURY ELECTRO-CHEMICAL COMPANY, NIAGARAFALLS, N. Y . , THE PIONEER IN AMERICAN PHOSPHORUS PRODUCTION
D
No scarcity of supply of phosphate rock need be feared within-&ion. Known American deposits contain some 6.5 billion long tons of rock, distributed in approximately the following manner:
Florida Tennessee Western states (Idaho, Montana, Utah, Wyoming) Other states
EVELOPMENTS in the manufacture of phosphorus and its derivatives have lately turned the spotlight on this branch of chemical industry. Recovery of elementary phosphorus, its shipment in tank car quantities from the point of recovery to plants elsewhere for conversion to customary compounds, and the role of the element as an intermediate in the production of phosphorus derivatives have been the salient features of present progress. Although none of these developments is new, yet implications in the scale on which they are practiced amply justify consideration and analysis. To understand the significance of present trends, it is necessary to consider the American phosphorus industry as a whole and some aspects of its development. Like all chemical industry, this branch has been continuously striving for lower costs, larger scale production, and higher use efficiency in its products. From simple processes, whose principal virtue was the yield of a desired material, the industry has striven for higher quality production on enlarged scales through the application of continually improved processes and equipment. Both have evolved into more intricate and precise patterns. Present interest centers about a current phase of a progressive evolution. At the moment no end point appears to have been reached in the process of change; and this, like other similar surveys, must be considered a snapshot of changing events, subject to all the limitations of that genus. The present phase of phosphorus development emphasizes economics. Because the value of ores of phosphorus de-
Total
546,000,000 103,000,000 5,745,000,000 121,000,000
6,515,000,000
The average annual output of United States mines since 1919 has been 3,100,000 long tons. The lowest production was 1,698,148 long tons in 1932, and the highest, 4,259,466 long tons in 1937. Obviously no lack of raw material need be feared by the phosphorus industry nor are measures of conservation now vital. The number of long tons from United States mines sold or used in 1937 was: Florida Tennessee (and Virginia) Idaho Montana .
Total
2,996,820 825,099 83,436 48,884 3,954,239
United States exports of phosphate rock in 1937 were 1,052,802 long tons, Florida mines being the principal exporters. I n comparison, imports are trifling-l3,400 long tons in 1937. The ore itself is a more or less impure apatite, CaloFa(P04)s. Although this mineral is recovered in reasonably pure form as a by-product of the working of nelsonite in Virginia, the quantity produced is small and the phosphate rock of commerce has an average phosphorus content of about 14 per cent (tricalcium phosphate equivalent 70 to 72 per cent) instead of the 18.5per cent contained in the pure 967
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 30, NO. 9
mineral. I n commercial grades the phosphorus content varies from below 12 to above 17 per cent (apatite). Consumption of phosphate rock in the United States in 1937, as reported by the Bureau of Mines, was distributed as follows: Su erphosphate OtBer fertilizer uses Stock and poultry feeds
Phosphates, phosphoric acid, ferrophosphorus
Total
%
Lone tons 2,391,245 129,655 3,324 429,805
79.3 4.3
2,954,029
100 0
0.1
16.3 ~-
The total of this group of tonnages does not exactly agree with other compilations, probably because of differences in sources of information, yet it serves as a basis for comparing the magnitudes of the important demands for phosphorus compounds. For present purposes, superphosphates (79.3 per cent of the total) and chemical uses (16.3 per cent) are of special interest. The remainder, 4.4 per cent, has no chemical implication and hence no share in the present discussion. Thus, phosphorus consumption is made up of a background of low-priced, relatively crude superphosphate for fertilizer purposes and a much smaller demand for higher priced, relatively refined compounds. The latter manufactures are considered, in the strictest sense,, part of the chemical industry. Superphosphate production is the backbone of the fertilizer industry, and although strictly chemical in its operations, is generally considered part of this specialized branch of the chemical industry proper. From the point of view of chemical elaboration of phosphorus compounds, superphosphate production is a huge consumer able to absorb excess output of higher grade phosphates whenever necessary. The existence of a huge market for phosphates and phosphoric acid in fertilizers is often thus used as a stabilizing influence by makers of high-grade products, despite the fact that serious price sacrifices are involved. I n the past this factor, together with the use of a common raw material, has been the only link between these two branches of the phosphorus industry. Recent developments in concentrated fertilizers, involving phosphoric acid or anhydride as the acidulating agent instead of the customary sulfuric acid, are tending to bring the two closer together. Chemical utilization of phosphorus and its compounds will receive first attention here because it is the more rapid recent development and its influence is extending into the fertilizer field.
Chemical Utilization
Photo by H . A . Marple; Courtesy, Monsanto Chemical Company
(Above) WHENDRAGLINE SCRAPERS HAVEREMOVED MOSTOE THE PHOSPHATE MATRIX FROM BETWEEN LIMESTONE “HORSES, HANDLABORIs NECESSARY TO CLEAN UP WHATIs LEFT (Below) TAPPING SLAGAND FERROPHOSPHORUS FROM A PHOSPHORUS
ELECTRIC FURNACE
The chemical history of phosphorus is involved in an intricate maze of processes first applied on a laboratory scale long ago and later, from time to time as need arose, developed into plant-scale operations. Here, as in most chemical developments, questions of priority present almost insuperable difficulty. Elemental phosphorus has been made for decades in quantities required by existing demands by an electric furnace process differing only in detail and in scale from that now receiving special attention. The manufacture of phosphoric acid by burning phosphorus and absorbing the phosphorus pentoxide produced in water is by no means new. However, despite the age of the processes involved, their present development is an important forward step for the industry. n’early a million tons of phosphorus as phosphorus pentoxide were utilized in 1937 in the United States. Nearly 84 per cent of this goes into fertilizers, principally in the form of superphosphates made simply by treating the ground phosphate mineral with acid. Sulfuric acid forms the ordinary superphosphate having 16 to 20 per cent available
SEPTEMBER, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
Pz05, and if phosphoric acid is substituted for sulfuric acid, the product may carry as much as 48 per cent available Pz05.The latter and other high-concentration phosphates represent,, a t present, only a trifling fraction of the total fertilizer phosphorus-at most, a few per cent. Of the remaining 16 per cent of our total phosphorus consumption, which by comparison is considered high grade, the most important part goes into the manufacture of (a) phosphoric acid used for edible and pharmaceutical purposes, ( b ) of various phosphates used as water softeners, medicinally, and in foods (particularly as leavening agents), and ( c ) of a number of other chemical compounds of diverse applications. The actual share of even this small part of the total which has been sold as elemental phosphorus has been a small item, and this small share has been almost entirely consumed in the manufacture of phosphor copper and similar alloys. On all of these, the new phase of phosphorus is having its effect, already evident and foreshadowing even greater consequences in the future. Phosphoric acid has been made traditionally by treating finely ground ore with dilute sulfuric acid, separating the insoluble calcium sulfate and gangue, and concentrating the decanted solution. Using continuous decanters and other modern efficient equipment, phosphoric acid of high grade is produced by this method after being concentrated and purified. The difficulties of this operation lie in the necessity for diluting the original mix to secure reaction (this requires that the acid product be concentrated subsequently) and in the cost of purification. Most important of the impurities are compounds of iron and fluorine which are difficult and expensive to remove. A further drawback to this wet process is the concentrating step necessary to yield acid of high concentration. The reaction involved is simple:
+
Ca10Fz(P04)8 10HzSOl = 10CaSOc 6H8POa
+
969
ence upon which the present new phase of development is built. Electric-furnace phosphoric acid is produced by a series of reactions somewhat as follows: 15C = CalnF9(POIIA 9SiO.
+
+
The charge consists of coke, phosphate, and silica. Ground phosphate and an amount of silica to produce the desired ratio of silica to lime are nodulized or sintered to minimize dusting before being charged into the furnace. The actual proportions of silica and carbon for optimum production may vary considerably from the theory as shown in Equation 1. The slag of calcium silicate and fluoride collects in the furnace bed in molten condition to be drawn off a t intervals. With the slag, ferrophosphorus collects; the €atter contains 25 per cent phosphorus formed by the reduction of the iron in the furnace charge in the presence of phosphorus. The mixture of phosphorus vapor and carbon monoxide produced by the furnace was originally burned with air to yield phosphorus pentoxide. This is washed out of the fume with water or phosphoric acid in scrubbing towers, which may be (and usually is) followed by a Cottrell precipitator to catch mist that escapes the scrubbers. The conditions of absorption, particularly temperature, determine the proportions in the mixture of the several phosphoric acids formed in the scrubbers (reactions 3A, B, and C). Most of the fluorine in the original ore is held in the furnace slag, only part of it escaping as silicon
+ 2HF
Because silica is present, the hydrofluoric acid is largely evolved as silicon tetrafluoride (SiF,) and fluosilicic acid (HzSiF6). Development away from this process in the United States began during the World War with the manufacture of ferromanganese in Alabama. Electric furnaces there yielded the much needed alloy. Feverish production stopped suddenly with the end of the war. Idle plant and idle capital sought new work to do. Minor alterations of furnaces and a different charge could produce phosphorus. This could be readily burned to phosphorus pentoxide and dissolved in water to yield phosphoric acid. Because the phosphorus had been volatilized, the acid was purer than that from the wet treatment of phosphate with sulfuric acid, and because phosphorus pentoxide is readily dissolved in either water or phosphoric acid, the product is obtained in high concentration without costly treatment. This operation developed on electric power; and while phosphorus was produced only as a n intermediate in the operation, it formed the basis both in fact and in experi-
THE BLASTFURNACE FOR RECOVERO YF PHOSPHORUS Is SIMIIRON BLAST FURNACE
LAR TO AN
Slag pit in foreground. skip hoist for charging a{ right: gas main taking phosphorus to stoves at left
Courtesy, Victor Chemical Works
Photo by H . A . Marple; Courtesy, Monsanto Chemical Company
CHEAPAND ABUNDANTELECTRIC POWERIs THE BASISOF ELECTRIC FURNACE RECOVERY OF PHOSPHORUS These lines lead current into the plant.
fluoride, and hence purification of the acid produced is minimized.
Economic Considerations Naturally the question of economy entered the picture. Electricity was used solely as a means of supplying heat. Other makers of phosphoric acid and phosphates, less fortunate with respect to power, looked elsewhere. Development of a blast furnace process using fuel directly was undertaken. Commercial success was achieved in this tedious and difficult task by Victor Chemical Works, and blast furnace production of phosphorus to be burned directly to phosphorus pentoxide became a reality. The reactions in the blast furnace, which may or may not involve intermediate steps not occurring in the electric furnace, use the same raw materials to produce the same products. The essential operating differences between the two are those inherent in the two methods of heating. An excess of coke is charged with the blast furnace burden of briquetted phosphate and silica, and air is blown through to burn the fuel and supply the heat necessary for reaction. I n consequence, the gases vented from the furnace contain a large proportion of nitrogen, carbon monoxide in addition to that formed in the reaction, and phosphorus vapor. These hot gases, mixed with more air, are burned and robbed of the major part of their heat content in stoves similar to those operated with iron blast furnaces. Stoves are run in pairs to store heat from the furnace exit gases and give it up to air being blown into the charge. Further cooling of the gases by water sprayed on the pipes precedes scrubbing to remove and convert their phosphorus pentoxide content to phosphoric acid. Both electric furnace and blast furnace processes yield elemental phosphorus as their first product. Heretofore this phosphorus has generally been burned immediately without separation from the accompanying gases, and the oxide has been absorbed in water to yield phosphoric acid. The latest development in this field has been to condense the phosphorus vapor and separate it as a linuid from its admixed gases. This 970
has always been possible and has been general practice of phosphorus manufacturers. It has been done onIy to a minor extent by phosphoric acid makers. Availability of cheaper electric power from operations of the Tennessee Valley Authority gave new impetus to the development of electric furnace production of phosphorus in Tennessee. I n 1937 this reached the point of recovery of el+ mentary phosphorus from raw mineral a t the mine and its shipment in tank cars to points of use. A n apparently simple step from making and burning phosphorus directly, the insertion of a distance of several hundred miles between the making and the burning of phosphorus is highly significant. On it hinges a series of consequences, some of which can be pointed out here. If raw phosphate is to be mined and shipped over considerable distances, and if its values are to be recovered by treatment with acid, these costs go up in proportion to total cost of the ultimate product as the grade of rock goes down. Mining, by hydraulic methods in Florida and by dragline scraper in Tennessee, is too small an item of product cost to be significant. However, processes of enrichment must be applied t o much of the product of mines to reduce freight and processing costs. I n Florida, flotation methods yield merchantable rock from low-grade fines. With cheap power available from the Tennessee Valley Authority’s developments, electric furnace recovery of elemental phosphorus is preferred there as a method of concentration. Low-grade ores, already containing silica in nearly the correct ratio to lime, may be actually cheaper to process than higher grade phosphate to which silica must be added. The element, phosphorus, is made available in high purity to chemical industry a t low cost by processing ore a t the mine. The immediate effect is on the phosphoric acids and their direct derivatives. The whole field of the phosphoric acids and of phosphates derived from them is being given a thorough overhauling as a result. With phosphorus pentoxide available a t chemical plants generally, these compounds can be produced in greater purity and a t lower costs than from wet process acid. Even the shipment of the acid itself becomes quite a different affair when the high concentrations of phosphorus pentoxide in meta- and pyrophosphoric acids are considered. Already a concentrated acid, called “tetraphosphoric,” containing 84 per cent PzOb and hence equivalent to nearly 116 per cent H8P04is being marketed. This acid corresponds to oleum in sulfuricacid technology and is the most concentrated solution of phosphorus pentoxide which is liquid under commercial conditions. For purposes of shipment it is to be contrasted to 75 per cent H3P04(equivalent to 55 per cent Pz05), now the common product, as well as with the element itself. Comparison with phosphorus is also necessary, because, when the element has reached the place of economic utilization, only air and water are required to convert it to acid of any concentration desired. Freight rates are not necessarily based on ton miles but rather take into consideration the value of the material hauled and any hazard connected with it. For this reason rates on elemental phosphorus are higher than on phosphorus compounds, and theeconomicalgeographicalradius of its shipment is greater, but not necessarily in proportion to phosphorus concentration. For example, over a strictly comparable haul where the rate on phosphoric acid is 33 cents per hundred pounds, that on elemental phosphorus is 53 cents per hundred pounds. The advantage of shipping phosphorus instead of 75 per cent H3P04over this distance lies in the fact that the cost of shipping the 23.7 pounds of phosphorus represented by 100 pounds of this acid is only 12.56 cents as against 33 cents, a saving of approximately 62 per cent. Even if tetraphosphoric acid, equivalent to 84 per cent PzO6, is considered for comparison, the shipment of the 36.7 pounds of phosphorus con-
tained in 100 pounds of this acid costs only 19.5 cents as conipared with 33 cents for the acid itself, a saving of 40 per cent. A further important factor in the situatiuri is Lhe fact that distilled phosphorus is practically free from fluorine. Even the gases direct from the furnaces in which it is made contain some fluorine. If these are burned directly and the phosphoric anhydride dissolved from them in water, a small residual amount of fluorine appears in the acid produced. By condensing the elemental phosphorus from the furnace gases, the fluorine content is still further reduced, and acid made by subsequent burning of liquid phosphorus is practically f l u e rine-free.
Compounds Utilized Present commercial developments are all based upon what amounts to a slight change in the practice of the makers of phosphoric acid hy volatilization. Advantage is taken of electric furnace production of the element to free it from fluorine and to put i t into convenient form for economical shipment. These are the present important implications in the development. However, beyond present industrial activity lie many possibilities which may become realities. Pure phosphorus pentoxide, available a t will wherever desired, suggests further development of the meta- and pyrophosphoric acids and their derivatives, &s yet minor products in a commercial sense. Widened fields of usefulness of the chlorides and oxychlorides of phosphorus are not beyond present vision. Phosphides, too, may he found valuable beyond present expectation when the possibility of their economical manufacture is realized. In final analysis, the essential differences between the present phosphorus industry and its predecessors are those of de. pee. In 1937 the three-unit electric furnace plant of the Monsanto Chemical Company a t Columbia, Tenn., began production of elemental phosphorus and its shipment in tank car quantities. In 1937, too, theelectric furnace plant of the
Cosrfesy. Victor Ciemicnl Woiks
Commercial compounds of phosphorus on which statistical data are available are shown in the following table (the data for 1935 are thelatest to he had): Phmphorio add (baris W % HDPO.) p 1 9 m phosphate, momCsloium phosphate. and tiiSodium phasphate. liiSodium phosphate, diSodium phosphate met* Sodium phosphste: mow- and PYTO.
*-
Short tons 22,459 35,862 4,729 87.108 35.435 5,147 4,517
In addition to these items, hypophosphites, glyoerophosphates, Fhosphorus chlorides, and phosphoric acid esters are commercially important hut comparable data on them are not available. Obviously monocalcium phosphate and diand trisodium phosphates are the most important of these. The effect of shipment of elemental phosphorus to points of manufacture near consuming markets is evident when the percentages of phosphorus in these compounds are compared: Sodium phasphate: N*PO.-12H%O
NMHI'O~ NaJIPOo7H+0 NanHPOrIZH~O NaHPOeZH,O NBPOL NacPsO, NdWvI0H~0
NarH&Or
METAPHOSPHATE AS MADS BY THE TVA Is A TILAXSPARENT GLASSVAR~OUSLY COLORED BY ITSIMPURITIES CALCIUM
%P
8.16
24.04 11.57 S.60
23.32 11.04 27.94
Calcium phosphate: CeH4PO.lvH~O CaI3P01-2H.0 CSl(POc1, CS(POd, Phowboiio acid:
HaPOa
%P 24.60 14.31 19.99 31.32 31.02 23.72 15.81
Markets Markets for phosphorus derivatives other than as fertilizers can be conveniently divided into four major groupsfood, water treatment, phosphate esters, and miscellaneous. Food uses of phosphates and phosphoric acid, in which for present purposes must be included pharma,ceutical requirements, hulk large with respect to all hut fertilizer applications. Many baking powders contain phosphates as their acid constituents. Sodium acid pyrophosphate and the acid orthophosphates of calcium, sodium, potassium, and ammonium have been so used, the last two in relatively small proportions. Phosphoric acid itself is a common art.icle of
American Agricultural Chemical Company a t South Amhoy, N. J., went into production with a single unit, which had already been enlarged beyond original plans. This was followed by the electric furnace plant of the Phosphate Mining Company at Nichols, Fla., a single unit plant. With these developments in progress, the Victor Chemical Works started the erection of a two-unit electric furnace plant near Mount Pleasant, Tenn. Meanwhile the Tennessee Valley Authority has been operating a three-unit electric plant a t Wilson Dam, Ala., turning out phosphorus for conversion into concentrated fertilizers for its large-scale agricultural experiments. 971
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INDUSTRIAL AND ENGINEERING CHEMISTRY
diet as a constituent of soft drinks to which it imparts tartness. The quantity included in each glass or bottle of drink is of the order of a few milligrams, but because the number of such drinks consumed runs into several hundred millions annually, the soft drink industry buys tonnage quantities of pure acid. Numerous phosphates, hypophosphites, and glycerophosphates are required in medicine, an important but not a large consumption of phosphorus. With these may be included pure calcium phosphate added as a source of both calcium and phosphorus to the diet of men and animals. For these purposes stringent specifications of purity must be met by manufacturers. Fluorine, particularly, must be kept a t an absolute minimum, as must other foreign substances. These requirements can be easily met by products of distilled phosphorus with a minimum of purification. Water-treating reagents are large consumers of phosphorus. Trisodium phosphate is an important water softener and a valuable mild alkali for inclusion in washing compounds. Lately sodium hexametaphosphate has come into prominence in this field on account of the relatively high solubilities of calcium and magnesium metaphosphate complexes and the valuable detergent properties of the compound. Organic esters of phosphoric acid, particularly triphenyl, tricresyl, and tributyl phosphates, are valuable plasticizers. Although these can be made from phosphorus pentoxide and the respective alcohols, the preferred method is to condense phosphorus oxychloride with the alcohols. These compounds are finding expanding markets in plastics and synthetic finishes. Into the class of miscellaneous uses of phosphorus compounds fall the corrosion inhibitors and rust-proofing treatment for ferrous metals. Phosphoric acid solutions with oxidizing agents are used in the rust-proofing processes known as “Parkerizing” and “Bonderizing” as applied to ferrous metals. Phosphates of sodium and ammonium and the phosphate esters are flameproofing reagents for textiles and wood. Processes yet in development or in the early stages of commercial operation suggest expanding uses for phosphorus and its compounds. Phosphoric acid as a petroleum-refining reagent and as a catalyst for polymerizing olefins is a growing commercial reality with a demand already in the hundreds of tons annually. Organic phosphates, particularly the glucose phosphates, offer some promise as special fertilizers on account of the fact that they are easily disseminated to deep-lying root systems in the soil solution.
Fertilizers Effects on fertilizers and soil character are a t present side issues in the minds of commercial developers of phosphorus, yet it is probable that the new phase of phosphorus may have more significant effects here than in any other field. Possibilities being actively explored by the Tennessee Valley Authority include metaphosphate fertilizers, made by passing hot phosphorus pentoxide from burning phosphorus over lump phosphate, and quick-curing triple superphosphate, made with orthophosphoric acid of high concentration. The metaphosphate fertilizers, containing 60 to 70 per cent PzOsof which 99 per cent is available, have further implications. A number of phosphate deposits in various parts of the country, those in Arkansas and East Tennessee among others, are too small to justify large investment in equipment for their exploitation. These can probably be worked with small inexpensive plants for converting their ore into metaphosphate, using phosphorus imported from large plants elsewhere. Similarly, immense deposits of phosphate in the far west are, in effect, moved closer to the great consuming
VOL. 30, NO. 9
markets by their conversion to phosphorus or to such highly concentrated fertilizers as calcium metaphosphate. The most obvious field for expansion is in fertilizer where the predominant part of our present output of phosphates is consumed. This field is being explored particularly by the TVA which seeks to improve agriculture and solve sociological problems by increasing the use of concentrated fertilizers in the seven southern states of its territory: Tennessee, Kentucky, Virginia, North Carolina, Georgia, Alabama, and Mississippi. Toward this end it is pioneering concentrated phosphatic fertilizers in an agricultural program developed to fit its conditions. In its fertilizer work, triple superphosphate is being made with 78 per cent phbsphoric acid, in turn made from phosphorus. This yields a dense, dry, granular product which requires a minimum of seasoning and no drying (either artificial or natural) and which does not rot ordinary fertilizer bags as does the product made with weaker acid. Some 100000 tons of this product have been made since November, 1934, and the greater part of it used by experiment stations, by the AAA, and by the more than twenty thousand farms cooperating in the TVA farm program. About a thousand tons of calcium metaphosphate have been made by the direct action of hot PZO5furnace fumes on lump phosphate rock and this, too, is going into its agricultural experiments. Its third major project is based on the increased solubility in ammonium citrate solution of natural phosphate whose fluorine content has been removed by calcining in the presence of steam and silica. This treatment increases the availability of the phosphorus pentoxide content of the rock as a fertilizer. Its simplicity suggests its use as a preliminary processing step for rock to be used in various other ways. These operations of the Tennessee Valley Authority are not commercial in the competitive sense. Not only is TVA fertilizer not marketed in competition with existing suppliers but the uses to which it is being put in the TVA farm program are developmental rather than competitive. I n effect the present program is designed to promote a saner agriculture and with it a demand for fertilizers of high concentration which ultimately will have to be met by the fertilizer industry.
Possible Uses Organic derivatives of phosphorus (as distinct from phosphoric acid esters) are noted in the literature by the literal hundreds, but none of them is of present commercial significance. I n fact our knowledge of any of them is yet too scant to permit any judgment of their value. They may open entirely new fields when their possibilities are more fully explored. The compounds of phosphorus with such common elements as oxygen, hydrogen, and the halogens involve intricacies that invite investigation. The phosphoric acids-ortho-, pyro-, meta-, and others-formed by different degrees of hydration of phosphorus pentoxide, offer in themselves an interesting field for research. The phosphorus compounds related to phosphine (PH,), which is a by-product of hypophosphite manufacture, and corresponding to the amines, invite investigation, particularly in view of the changes in character produced by substitution of different groups for hydrogen in the original molecule. The amphoteric character of the phosphorus atom and its two valences of 3 and 5 suggest other values to be realized from it yet unguessed. New alloys of phosphorus with metals may add importantly to our metallurgical raw materials. Recent researches have shown that phosphorus produces effects in steel quite different from those formerly credited to it but now traced to other constituents in the metal. RECEIVED May 24, 1938.
