Double Salts of Calcium and Potassium and Their Occurrence in

Double Salts of Calcium and Potassium and Their Occurrence in Leaching Cement Mill Flue Dust. E. Anderson. Ind. Eng. Chem. , 1919, 11 (4), pp 327–33...
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Am., 1919

T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY

327

M ' ? e I1

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u

Meter

PLAN .VIEW

"I1i1

ELEVATION

FIG. 1-TANK USED FOR A ~ R A T I OON B EFFLUEKT FROM

cidental. I n each method 7 0 per cent of t h e sulfur dioxide was removed in 30 min. aeration, but with 97,000 cu. f t . of free air per million gallons of effluent when operating continuously, as compared with 87,000 cu. f t . per million gallons on the fill-and-draw plan. T h e aera.ted effluent did not de-aerate the diluting water t o a n appreciable amount a t any time, and thus could be discharged into t h e harbor with safety. Bacterial counts made by Mr. W. S. Sturges before and after aeration showed t h a t there was practically no change in t h e bacterial content. Laboratory experiments in which wood plates were used for diffusing t h e air indicated t h a t the amount of air. required could be reduced considerably b y diffusing t h e air very finely. This experience is similar t o t h a t found in the activated sludge experiments a t Milwaukee, but it is probable t h a t this oxidation, which is purely chemical, is even more affected by t h e fineness of division of t h e air t h a n is t h e oxidation in t h e axtivated sludge process, which is biological. T h e quantities of air used in t h e experiments with t h e filtrose diffuser were from one-fifteenth t o onetwentieth of those used in the aeration with activated sludge, so it is probable t h a t t h e cost of this aeration would be low. T h e tank used for t h e aeration was too shallow t o be very efficient, and it is believed t h a t the results obtained in these experiments could be greatly improved b y further work. While this aeration will make a Miles plant more complicated and t h e process more costly, it does not necessarily condemn t h e process, as t h e aeration period is very short and

THE

MILESACIDPROCESS

the amounts of air necessary b u t a small fraction of those required in t h e activated sludge process. CONCLUSIOKS

I-The Miles acid effluent contains unoxidized sulfur dioxide. 11-This sulfur dioxide is oxidized a t t h e expense of t h e dissolved oxygen in the water in which t h e effluent is diluted. 111-The sulfur dioxide may be oxidized before dilution b y aeration for a short time with relatively small quantities of air. After this aeration t h e effluent will not de-aerate large volumes of diluting water. DEPARTMENT OF HEALTH HAVEN,CONNECTICUT

NEW

DOUBLE SALTS OF CALCIUM AND POTASSIUM AND THEIR OCCURRENCE IN LEACHING CEMENT MILL FLUE DUST By E. ANDERSON Received August 13, 1918

T h e recent development of t h e cement potash industry has served t o direct attention t o certain double salts of potassium and calcium which have heretofore been of interest chiefly t o t h e scientific investigator. Of these t h e potassium mono-calcium sulfate, KzS04.CaS04.PIz0, or syngenite, is perhaps most familiar, b u t t h e potassium penta-calcium sulfate, KzS04.j C a S 0 4 . H 2 0 , is equally important. The occurrence of these salts in t h e natural potash deposits and t h e fact t h a t they can be easily made artificially from their simple constituents indicates t h e possi-

3 28

bility of the formation of such compounds in solution from potash-bearing flue dust, since such dust nearly always contains both potassium a n d calcium sulfates. Numerous papers have been published during t h e past years by both German and American investigators discussing fully t h e nature a n d properties of these compounds, and rather complete d a t a on t h e conditions necessary for their formation and existence are therefore available. A knowledge of these relationships is important in dealing with t h e problem of leaching potash from cement mill flue dust, a n d as i t appears as though t h e original articles referred t o have escaped t h e notice of most of t h e chemists now engaged in this field of potash manufacture, a rBsum6 of t h e d a t a from these papers may be of interest. We owe much of our present knowledge about t h e double salts of potassium and calcium t o the investigations carried on by J. H. van’t Hoff from 1897 t o 1908 on t h e formation of t h e Stassfurt salt deposits. Van? Hoff was assisted in this work by a number of investigators from many parts of t h e world. The list of names of these coworkers shows how thoroughly cosmopolitan the group was, as one reads, for example, 0. Biach, W. C. Blasdale, D . Chiaraviglio, and F. G. Cottrell. Three double sulfates of calcium and potassium appear t o have beeri studied by these investigators. These were potassium mono-calcium sulfate, KzS04. C a S 0 4 . H 2 0 ; potassium di-calcium sulfate, KzS04. zCaS04.3H20; a n d potassium penta-calcium sulfate, KzS04. 5 C a S 0 4 . H z 0 . Of these, t h e potassium mono-calcium sulfate, t o which has been given the shorter name of syngenite, seems t o have been t h e first t o be identified. This double salt was apparently first made artificially as early as 1850.’ Shortly after this a double sulfate of potassium a n d calcium was found in the Stassfurt salt deposits, a n d was named kaluszit. Later on, however, this natural salt was identified as the potassium monocalcium sulfate, and t h e mean was subsequently changed t o syngenite,2 which name has, however, only recently become familiar t o t h e industrial chemist. This double salt, syngenite, may be prepared by dissolving 1 2 0 g. KzS04 in 1000cc. of water and adding t o this I O O cc. of a 20 per cent solution of CaC12. At first gypsum separates out and this is then converted into syngenite, which appears under t h e microscope a s square-ended needle-like crystals. These can again be converted into gypsum by the addition of water. Potassium di-calcium sulfate, KzS04. zCaS04.3 HzO, has been described by Ditte,3 b u t later investigators seem t o have failed t o prepare this salt from solutions of potassium sulfate. Thus van’t Hoff a n d Geiger4 investigated solutions a t 83’ C. while J. D’Ans and Jahrrsber., 1850, p. 298. 2 Ibid., 1850, p. 1142. 8 Comfit.rend., 1811, pp. 84-86. 4 “Untersuchungen der ozeanischen Sakabidgerungen,” p. 276. I

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Schreiner’ worked a t temperatures between 140’ C. and 170’ C. without positive results. D’Ans states, however, t h a t a potassium di-calcium sulfate had been prepared from the fused mixture of the two salts. Potassium penta-calcium sulfate, was first prepared by van? Hoff and Geiger2 by boiling precipitated calcium sulfate with a s per cent solution of potassium sulfate. T h e potassium pentacalcium sulfate then forms in well defined crystals, similar in appearance t o those of gypsum. The equilibrium conditions between 0’ C. a n d 83’ C. for t h e formation of both syngenite and t h e pentacalcium salt have been determined by various investigators. Syngenite is stable in solutions of t h e proper concentrations a t all temperatures investigated, t h a t is, between o o C. a n d 170’ C. Potassium pentacalcium sulfate, however, is only stable above 31.8’ C. From o o C. t o 31.8’ C. syngenite is t h e only stable double salt. T h e concentrations of potassium sulfate necessary for, t h e equilibrium represented by t h e equation CaSOd.zH20

+ KzS04

K2S04.CaS04.H20

+ HzO.

(I)

varies with t h e temperature, t h e concentration increasing with an increase in temperature. At temperatures higher t h a n 31.8’ C. either of t w o double salts can exist, namely. t h e mono-calcium salt, or t h e penta-calcium salt. With lower concentrations of potassium sulfate t h e equilibrium may be established which is represented by t h e equation 5(CaS04.zHzO)

+ KzS04 KzS04.gCaS04.Hz0

+ gHzO.

(2)

With solutions of higher concentrations of potassium sulfate syngenite can be in equilibrium with t h e potassium penta-calcium sulfate as expressed in t h e equation KzS04.5CaS04.H~O

+ qKzS04 + 4 H z 0 1_

5 (KzS04.CaS04.HzO).

(3)

T h e concentrations for t h e equilibria referred t o have been determined, as previously mentioned, by various investigators such as van’t Hoff and his coworkers in GermanyS and Cameron a n d Breazeale4 in America. J. D’Ans has compiled much of these d a t a in a n article entitled, “Investigations of t h e Calcium Alkali Sulfates.”6 The d a t a given in t h a t article, together with t h e concentration-temperature diagram accompanying same, show clearly t h e conditions necessary for t h e formation and existence of t h e two double salts, syngenite a n d potassium penta-calcium sulfate. The following tables give the concentrations of potassium sulfate required t o establish equilibrium with syngenite a n d potassium penta-calcium sulfate at t h e temperatures stated. 1

Z . anorg. Chem., 6 2 , 129-67.

3

“Untersuchungen der ozeanischen Salzablagerungen,” p . 275. HOE, “Untersuchungen der ozeanischen Salzahlagerungen.” J. P h y s . Chem., 8 (1904). Z . anorg. Chem., 6 2 .

a Van’t 4

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TABLE 1:-€$QUILIBRIUM

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CONCENTRATION OF SOLUTIONS OF POTASSIUM

enough t o permit solid potassium sulfate t o separate To make this clear t h e solubility curve of potasout. SULFATE.OR GYPSUM Mols. &SO4 Mols. &SO4 sium sulfate has been added t o t h e diagrams. If, then, TEMP. per 1000 mols. per 1000 g. c. HzO Soliition Solid Phases gypsum be added t o solutions containing over 2 . 0 7 0 2.1 per cent potassium sulfate it will finally all be con: ] Synsenite, gypsum 3.22 25 31.8 3.70 0 . 2 0 Syngenite, gypsum, penta-calcium salt verted into syngenite, provided t h a t the potassium 40 4.4 0.23 sulfate concentration be maintained. 60 6.8 0.35 Syngeuite and penta-calcium salt s3 9.9 0.50 I t is evident from t h e diagram t h a t the equilibrium concentration of potassium sulfate necessary for TABLE 1 I-€$QUILIBRIUM CONCENTRATIONS OF SOLUTIONS OF POTASSIUM SUGFATE AND SOLID POTASSIUMPENTA-CALCIUM t h e formation of syngenite increases rapidly with t h e SULFATE AND GYPSUM A t 31.8' C., however, a new double temperature. Mols. &So4 Mols. &SO4 salt can form, namely, potassium penta-calcium sulTEMP.per 1000 mols. per 1000 g. c. Hz0 Solution Solid Phases fate. This temperature and the corresponding solu31.8 3.70 0.20 Syngenite, gypsum, penta-calcium salt 40 3.8 0.203 Penta-calcium salt, gypsum tion concentration therefore make a triple point, 60 2.4 0 . 130 Penta-calcium salt, gypsum 83 1.3 0.070 Penta-calcium salt, gypsum where t h e solid phases gypsum, potassium pentacalcium sulfate, and syngenite can exist in equilibrium The d a t a for t h e concentration of calcium sulfate with t h e solution, this solution containing 3.50 per in these solutions appear only for o o C. and 2;' C. cent potassium sulfate and being saturated with reTABLE 111-EQUILIBRIUM CONCENTRATION OF Cas04 FOR SOLID SYNGENITEspect t o calcium sulfate. SULFATE AND SOLIDSYNGENITE, POTASSIUM PENTA-CALCIUM

$:

1

T~MP. C. 0 25

AND GYPSUM Mols CaSOa per 1000 mols. H20

0.113 0.223

Mols. of Cas04 per 1000 g. Solution 0.0064 0.012

I n the following diagram by D'Ans (Fig. I ) t h e d a t a from Tables I and I1 have been plotted so as t o more clearly show t h e relationships expressed. I n practice, the concentration of solutions is more often given as grams per liter, or as per cent. While no d a t a were given in t h e paper referred t o on t h e densities of t h e solutions in question, so as t o permit the calculation of t h e concentrations in grams per liter, a diagram (Fig. 2 ) has been constructed giving these values in per cent by weight, which may be of interest in comparing commercial solutions. This curve is based upon t h e following calculated d a t a : TABLEEV-EQUILIBRIUM CONCENTRATIONS O F SOLUTIONS OF POTASSIUM SULFATE IN CONTACT WITH SYNGENITE, POTASSIUM PENTA-CALCIUM SULFATE OR GYPSUM Per cent KzS04 Potassium PentaCalcium Sulfate Curve

c

TPMP.

c.

0.0 25.0 31.8 40.0 6 0 .0 83.0

Syngenite Curve 2.07 3.04 3.49 4.01 6.10

8.72

..

3:49 3.56

2.27 1.22

A consideration of the diagrams gives a clear idea of t h e conditions necessary for t h e formation and existence of these double salts. Thus, a t 0' C., gypsum is stable in saturated solutions o l calcium sulfate which contain up t o 2 . 0 7 per cent of potassium sulfate. If syngenite crystals Were placed in such solutions they would break up into solid CaS04.zH20, with simultaneous solution of potassium sulfate. At exactly t h e concentration given, namely, 2 . 0 7 per cent potassium sulfate, syngenite and gypsum are stable as solid phases. If solid potassium sulfate be added to such a solution, more syngenite will form in accordance with Equation I , a n d t h e potassium sulfate concentration will not permanently increase until all of t h e gypsum has been so converted. I n similar solutions of higher concentration of potassium sulfate, syngenite is t h e only stable solid except, of course, where the concentrations are high

FIG. 1

The equilibrium temperature and concentration for t h e triple point have been determined by several different investigators a n d are probably very nearly correct. It is therefore likely t h a t t h e value given for the concentration of potassium sulfate for t h e penta-sulfategypsum equilibrium a t 40' C. is too high. This is evidently the reason why t h e point was not connected in the curve of t h e D'Ans diagram. The equilibrium concentration for t h e penta-calcium salt decreases as t h e temperature increases from this triple point. If, then, a solution containing 3 . 4 9 per cent potassium sulfate is heated above 31.8' C. in contact with solid syngenite, penta-calcium sulfate, a n d gypsum, t h e syngenite a n d gypsum will be converted into potassium penta-calcium

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FIG.2

sulfate, t h e point on t h e plot being moved t o t h e right from t h e triple point i n t o t h e potassium penta-calcium sulfate field, as indicated by t h e dotted line a in Fig. 3. On t h e other hand, if t h e solution is cooled below 31.8" C. t h e penta-calcium salt together with t h e gypsum will combine with potassium sulfate a n d form syngenite, t h e point on t h e plot being moved t o t h e left from t h e triple point into t h e syngenite field, as indicated by t h e dotted line b in Fig. 3. Similarly in solutions having a concentration of potassium sulfate of 2 . 2 7 per cent t h e gypsum will begin t o combine with potassium sulfate a t 6 0 " C. t o form &Sod. jCaS04.HZO. At this concentration both gypsum and t h e pentacalcium sulfate are in equilibrium with t h e solution i n accordance with Equation 2 . If t h e temperature is raised above 60" C. and t h e solution concentration maintained with respect t o potassium sulfate, all of t h e gypsum will combine with potassium sulfate t o form KzS04.gCaSOe.H20, t h e point on t h e plot lying inside

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FIG.3

the potassium penta-calcium field along t h e dotted line c (Fig. 3 ) . On t h e other hand, if we s t a r t a t t h e same point, namely, potassium sulfate concentration of 2 . 2 7 per cent and temperature of 6 0 " C., and if t h e concentration of potassium sulfate be t h e n increased, t h e equilibrium will shift along t h e dotted line d (Fig. 3 ) . On increasing t h e concentration t h e gypsum will all be converted into potassium penta-calcium sulfate, this being t h e only stable solid phase. until a solution concentration of 6 . I per cent potassium sulfate has been attained. ,4t this point syngenite may form, b o t h potassium penta-calcium sulfate and syngenite being in equilibrium with t h e solution, in accordance with Equation 3, and as indicated in t h e plot. If t h e concentration of potassium sulfate be increased beyond this point and temperature maintained a t 6 0 " C. all of t h e potassium penta-calcium sulfate will be converted into syngenite, and this latter salt will then be t h e only stable phase until t h e

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T H E J O U R N A L O F I i V D U S T R I A L A N D E iVGI ATE E RI N G C H E M I S T R Y

solution becomes saturated with respect t o potassium sulfate, which will occur a t a concentration of I j . 3 8 per cent potassium sulfate. It appears from t h e published literature t h a t 83’ C. is t h e highest temperature at which equilibrium concentrations were accurately determined. D’Ans and Schreiner, however, obtained both syngenite and potassium penta-calcium sulfate from solutions a t between 140’ C. and 170’ C. Some tests are now under way in t h e laboratories of this company t o determine t h e equilibrium concentrations a t I O O O C., for t h e two double salts, syngenite and potassium penta-calcium sulfate. T h e information so far obtained indicates t h a t t h e curve representing t h e equilibrium concentration for gypsum and potassium penta-calcium sulfate does not change its direction to any great extent up t o t h e temperature of I O O O C. However, t h e d a t a obtained will not permit stating this with absolute certainty until t h e investigations are completed. According t o D’Ansl i t is probable t h a t at some higher temperature another triple point will be found where potassium sulfate, syngenite, a n d potassium penta-calcium sulfate will be t h e three stable phases and t h a t above this temperature t h e penta-calcium sulfate will be t h e only stable double salt. However, no accurate d a t a seem t o have been obtained with respect t o this question. The presence of other salts, such as chlorides of sodium and magnesium, necessarily affects t h e formation of these double salts. For example, D’Ans states’ t h a t syngenite and calcium chloride may be formed b y t h e interaction of gypsum and potassium chloride according t o t h e reaction:

+

zCaS04.2H20 zKC1 I f CaClz KzS04.CaS04.H20

+

+ HzO

(4)

Potassium penta-calcium sulfate and calcium chloride may :ilso be formed from anhydrite and potassium chloride. Sodium chloride retards these double decompositions a n d at 2 5 ’ C. t h e syngenite formation according t o Equation 4 does not t a k e place in solutions saturated with sodium chloride. I t is evident, therefore, t h a t t h e comparatively simple relations described in t h e case of solutions containing practically only t h e sulfates of potassium and calcium may become very complicated when many other salts are present, as is t h e case, for example, in t h e natural brines. It will be seen from t h e d a t a presented t h a t t h e crystallization of t h e different simple a n d double salts of calcium and potassium can be controlled b y properly regulating both temperature and solution concentration. I t will also be apparent t h a t t h e separation of one salt or t h e other from solution is dependent upon equilibrium conditions, which shift gradually with change in temperature a n d solution concentration, a n d t h a t consequently t h e r e is no so-called “critical point” or “critical temperature” at which t h e double salts break down into their sim1

Lor

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Kolz, 17 (1911)

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ple components, as some recent discussions would lead t h e casual reader t o assume. I n leaching t h e ordinary cement-mill flue dust with water, solutions may be obtained which will contain calcium and potassium sulfate of t h e necessary concentration for t h e formation of either or both of t h e double salts mentioned. Practically all fuel used in cement burning contains sulfur which leads t o t h e formation of sulfates, so t h a t t h e co!lected flue dust contains both calcium and potassium sulfates, I n addition t o these, however, there may also be present other sulfur compounds, carbonates, and hydroxides as well as smaller quantities of magnes‘um salts. It is, nevertheless, unlikely t h a t t h e equilibrium conditions found b y t h e investigators referred t o will be appreciably affected by t h e presence of such other compounds 2s long as t h e requisite amounts of potassium and calcium sulfates are present. Of course, in cement mills where t h e potassium in t h e co!lected dust is largely in t h e form of chloride a n d where sodium chloride is also present, t h e react’ons may differ, as indicated by t h e conclusions of D’Ans just referred to. I n considering t h e present discussion it should be remembered, however, t h a t t h e time factor involved in t h e for-mation of these double salts is exceedingly important. All figures discussed above indicate equiiibrium conditions, which in some cases are only reached after a considerable period of time, as t h e velocity of t h e reactions involved is apparently rather slow. For instance, t h e investigators referred t o in some cases allowed z t o 3 weeks for t h e preparation of t h e double salts and for t h e establishment of equilibrium conditions. I n applying t h e d a t a contained in this paper t o commercial operations t h e time factor must be borne in mind, for t h e time allowed for such operations will usually be too short t o establish even an approximation t o equilibrium conditions. If operations are carried on rapidly i t would be possible, due t o the slowness of t h e reactions involved, t o pass completely cver certain fields, as for example t h e penta-calcium sulfate field, without forming any appreciable amount of t h a t salt. Some tests have been made a t these laboratories t o determine t h e time necessary t o form these double salts from appropriate solutions. The following experiment will serve t o illustrate t h e importance of t h e time factor involved: A 6 per cent solution of potassium sulfate saturated with calcium sulfate and in contact with this salt was kept z z hrs. a t 70’ C. without any visual evidence of potassium penta-calcium sulfate formation, and with no loss of potassium sulfate from t h e solution. The same solution was then cooled t o zoo C. After 43 hrs. a t this temperature syngenite crystals were first noticed, b u t only after 66 hrs.’ standing a t zoo C. had a sufficient amount of potassium sulfate been precipitated as syngenite t o make an appreciable difierence in t h e potassium concentration of the solution. Identical results were also obtained with solutions of similar concentrations made from cement mill flue dust, where t h e dust was left in contact with t h e

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solutions. Under especially favorable conditions as regards concentration and temperature, syngenite has been observed after 3 hrs.’ agitation in solution from flue dust. Continuous leaching operations have, however, been carried on with practically saturated potash solutions. where t h e time of contact averaged one hour, with no sign whatever, either visual or analytical, of t h e formation of any of t h e double salts ref erred to. From the above i t will be seen t h a t during t h e leaching of cement mill flue dust for t h e recovery of potash, t h e operations may be so adjusted as regards time of contact and solution concentration t h a t t h e formation of double salts can be avoided a t whatever temperature is chosen as being t h e most desirable for t h e leaching operation CHEMICAL LABORATORY WESTERNPRECIPITATION COMPANY Los ANGELES,CALIFORNIA

THE EFFECT OF MANGANESE ON THE GROWTH OF WHEAT: A SOURCE OF MANGANESE FOR AGRICULTURAL PURPOSES’ By J. S. MCHARGUE

The object of t h e experiments in this paper was t o demonstrate t h e effect of manganese on t h e growth of wheat under different conditions and t o point out a source of this element for agricultural purposes. I n a study of t h e work of previous investigators on t h e relation of manganese t o agriculture and its probable function in t h e vegetable economy one is impressed with t h e lack of agreement in t h e results of t h e several investigators and, especially, with t h e variety of their conclusions. I n seeking a plausible explanation of t h e wide variations in t h e conclusions reached by the many investigators on this subject one must give attention t o t h e object t o be attained and t o t h e various conditions under which t h e different investigations were carried on. I n regard t o t h e object t o be attained, one class of investigators apparently have been interested in determining whether or not manganese has any commercial value from t h e standpoint of a necessary fertilizer, whereas t h e other class have sought t o determine whether or not manganese is a n essential element in t h e vegetable economy and, if so, its functions. Since t h e end t o be attained b y each of these different classes of investigators was not one and t h e same thing it is only natural t h a t considerable contention has arisen as t o whether or not manganese plays a definite rdle in agriculture. For example, an investigator having t h e commercial viewpoint in mjnd may add a manganese compound t o a soil already containing enough of this element and when he observes no effect on t h e growth of t h e crop he arrives a t t h e conclusion t h a t manganese has no important function in t h e growth of crops, t h u s failing t o take into consideration t h e amount of this element already contained in t h e normal soil. T h e most productive soils of Kentucky contain as 1 Read before the Division of Agricultural and Food Chemistry, CleveLand Meeting, American Chemical Society, September 12, 1918.

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much as 0.40 per cent of manganese,l whereas some of t h e least productive soils contain as little as 0.005 per cent.2 I n all probability t h e latter soils would respond t o an application of this element, whereas preliminary experiments show t h a t t h e former do not. It is, therefore, evident t h a t t h e failure on t h e part of those having t h e commercial viewpoint t o recognize t h e importance of manganese from an agricultural standpoint is due t o the fact t h a t no consideration has been given t o t h e amount of this element already contained in normal soils. Apart from t h e work of Bertrand, very little has been done t o prove whether or not manganese is a n essential element in t h e vegetable economy. After extended researches on t h e effect and function of manganese in t h e vegetable economy, this investigator arrives a t t h e interesting conclusion3 t h a t manganese Is, apparently, not t o be replaced by another element, not even by iron, and t h e small quantity of it occurring is no reason for regarding it as a secondary element in t h e composition of plants. As a result of his investigations on laccase, an enzyme occurring in plants, t h e activity of which seems t o be in some way associated with manganese, Bertrand concludes t h a t this element can no longer be considered as a non-essential, b u t t h a t it is a substance of vital necessity t o t h e functions of plant life. I n a more recent investigation he insists on t h e r8le of manganese in t h e functioning of t h e oxidizing enzymes, and still later investigations led him t o t h e conclusion t h a t manganese intervenes as a catalytic agent, in t h e material changes of which plants are t h e seat, and t h a t i t participates in a n indirect manner in t h e building up of t h e tissues and in t h e production of organic matter. An earlier investigation b y t h e writer,4 on t h e manganese content of various seeds, revealed t h e unsuspected and interesting fact t h a t t h e manganese was not uniformly distributed in t h e different parts of t h e seed b u t was confined almost entirely t o t h e thin, brown seed-coat which envelops t h e cotyledons and forms t h e inside lining of t h e outer epidermal layer or hull of certain seeds and nuts. For example, in case of t h e almond we find t h e greater part of t h e manganese, not in t h e hard outside shell nor in t h e cotyledons, b u t in t h e brown seed-coat t h a t surrounds t h e cotyledons. Again, in t h e case of t h e seed of wheat, we find only traces of manganese in either t h e chaff or t h e flour, and relatively large concentrations in t h e bran. The observation t h a t t h e greater part of t h e manganese contained in seeds is confined t o t h e seed-coat affords food for thought in regard t o t h e function of this element in plants and whether or not it is essential in t h e growth and normal development of their seeds. EXPERIMENTAL

The following experiments suggested themselves as a possible means of throwing further light on t h e question whether or not manganese is an essential element in t h e McHargue, unpublished results. Shedd, THISJOURNAL, 6 (1914), 660. 8 W. E. Brenchley, “Inorganic Plant Poisons and Stimulants.” Cambridge, 1914. 4 J . Am. Chem. SOC., 36 (1914), 2532. 1

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