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2. That colloidal manganese dioxide is especially easily obtained by incompletely oxidizing glucose (as well as fructose and galactose) in alkaline solution with potassium permanganate. 3. That the colloidal manganese dioxide is formed under these conditions first passes into a viscous or gel stage which subsequently changes into a limpid colloidal solution. 4. That the properties of the first stage agree well with those of a typical emulsoid, while the later stage seems more characteristically a suspensoid. 5. That the transformations of the emulsoid are typical and would be normal in every way if it were not for a slower but simultaneous transformation of the emulsoid into a suspensoid, owing to the effect of the alkali in accordance with the generalizations of Mayer, et al. 6. That both transformations are readily affected by variations in temperature, concentration of the reacting mixture and concentration of the alkali (KOH or NaOH). 7. That low temperatures are more favorable to the formation of the colloid. 8. That the concentrated colloid described here is readily coagulated by warming. 9. Suggestions are made indicating possible relationships between the remarkable properties of manganese in biochemical reactions and the properties of colloidal manganese dioxide as described above.
CHICAGO, ILL.
A CONDUCTIVITY STUDY OF THE REACTION BETWEEN CALCIUM NITRATE AND DIPOTASSIUM PHOSPHATE IN DILUTE SOLUTION.’ BY W. A. WITHERSAND ALEX. L. FEILD. Received January 7, 1915.
It is generally agreed that a soluble calcium salt reacts with dipotassium phosphate in the presence of an excess of ammonia to form an amorphous precipitate of tricalcium phosphate with no tendency to become crystalline on standing. When, on the other hand, ammonia is not added, there occurs a reaction in regard to which there is a great difference of opinion. The present investigation was made in order to determine the nature of the latter reaction.
Introductory. It has been known for some time that tricalcium phosphate, when precipitated in neutral solution, has a composition which only approximates to the theoretical, due to the hydrolytic action of the solvent. This 1 Read at the meeting of the N orth Carolina Section of the American Chemical Society, Raleigh, N. C., May 2, 1914.
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W. A . R'ITHERS AND ALEX. I,.
FEED.
hydrolysis has been studied by Warington', Georgievics, and recently by Cameron and Hurst;' dnd Cameron and Seidell. In these researches the solid tricalcium phosphate was added to a certain \*olume of water. Analyses vi ere made after equilibriiim conditions were reached. From a consideration oi the data a\-ailable. L'anieron and Hurst draw the following coiiplusioiic . "From these f x t s it appears that no matter what compound, or mixture of compounds, cmntaining only calcium and phosphoric acid (Can(P04),J, be placed in water there will result free phosphoric acid in the solution nith separation of calcium hydroxide. The calcium hydroxide may then react to form a more basic and less soluble phosphate, or simply form J. mixture a i t h the phosphate, the soliibility of nhich is decreased by its presence "
Furthermore, it was shown by Warington6 and verified by Cameron and Seidel16 that the decomposing action of water upon tricalcium phosphate depends upon the relative masses of the phosphate and water that are brought together. An extensive study of equilibrium conditions in the system, lime (Ca0)phosphoric acid (P20.5)- water, has been made by Cameron and Seidell,' and yet more fully by Cameron and Bell.8 The last-mentioned investigators conclude that in dilute solution, giving a neutral or nearly neutral reaction to phenolphthalein, the solid phase will be tricalcium phosphate or a soIid solution of nearly the same composition; and, furthermore, that il' there is a range of solution in equilibrium with tricalcium phosphate such a range would be very small. It will now he understood that a reaction involving the formation of tricalcium phosphate will not in general be a simple one, due to the partial hydrolysis of the tricalcium phosphate to a more basic phosphate or a solid solution, containing lime as one constituent. For the sake of convenience, however, we shall consider that the tricalcium phosphate formed corresponds in composition to the theoretical, whenever equations are given for the reaction between calcium nitrate and dipotassium phosphate. Any hydrolysis which takes place can be considered subsequently and independently. There is much disagreement among the text-books in regard to the reaction under consideration. Some give equations for the reaction which are so obviously incorrect that they will not be considered hereJ . C'hem. Soc., 26, 983 (1873) Moaalsk., 12,566 (18qr). THISJOURNAL, 26, 885 (1904). Ibid., 26, 1454 (1904). L O G . cit., p. 905. Loc. d t . TEISJOUXNAL, 27, 1503 (1905). 3 I&d.,27, 1512;28, 1222 ( I @ ) . I
2
A CONDUC‘i‘IVXTY STUDY OF CALCIUM NITRATE, ETC.
I093
such as the immediate formation of dicalcium phosphate. The various reactions which deserve our consideration are represented by the following equations : Equation I . (a) 4K2HP04 4Ca(N03)2= Ca(HzP04)2 Ca~(P04)~+8KN03. (b) Ca(H2P04)z Ca3(P0& = 4CaHP04.
+ + + Equation (a) 2K2HP04 + 3Ca(N03)2 = Caa(P04)2 + 2HN03 + 4KNO3. (b) 2HN03 + Ca3(P04)2 = 2CaHP04 + Ca(NO3)z. Equation 3. 4K2HP04 + ~ c a ( N 0 = ~ Ca3(P04)z )~ + 2KH2P04+ 6KN03. 2.
The second step in Equation I .is usually considered to take place very slowly, but more quickly upon acidifying. Equation I is given by Remsen.2 Similarly the second step in Equation. 2 would occur only after long standing. Lang and Kaufman3 give an equation analogous to (2) as being that generally accepted by texts as representing the reaction between silver nitrate and disodium orthophosphate. The present investigation makes use of conductivity measurements to determine what reaction, or reactions, actually take place when calcium nitrate is added in increasing quantities to a given quantity of dipotassium phosphate. The volume is kept constant. The concentration employed throughout the investigation is I g. of K2HPOeper liter, to which calcium nitrate is added in quantities up to 500 mg. nitrogen, as calcium nitrate, per liter. Whenever solutions of phosphoric acid or monopotassium phosphate are used, their concentration is equivalent to 0.5455 g. PO4 per liter, which is the amount of PO4 present in I g. of dipotassium phosphate. After deciding which equation correctly expresses the reaction, this conclusion is verified by determinations of the composition of the liquid phase a t various stages of the reaction. The method of conductivity titrations is employed for these determinations.
Method and Apparatus. The solutions of calcium nitrate used were standardized by precipitating as calcium oxalate and titrating the precipitate with O.IN permanganate, standardized by means of pure ferrous ammonium sulfate. The .phosphoric acid and phosphate solutions were analyzed by precipitating with magnesia mixture, igniting, and weighing as magnesium pyrophosphate. Duplicate analyses agreed very closely. Ostwald. “Principles of Inorganic Chemistry” ( ~ g o a )p, , Remsen, “Chemistry” (1890),p. 538. THISJOURNAL, 27, 1515 (1905).
522.
W. A. WITHSRS AND ALEX.
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L. FSILD.
The solution of potassium hydroxide contained a small quantity of carbonate, and was carefully protected from the atmosphere. It was standardized by a conductivity titration with hydrochloric acid, which, in turn, had been analyzed by weighing as silver chloride. The nitric acid solutiori was similarly standardized by the conductivity method against the standardized potassium hydroxide solution. Both of these solutions had a normality of O . O j 7 4 . I O cc. of either acid or base reacted with 100 cc. of the phosphate solutions, according to equations which will be given later. The same cell was used in all measurements of conductivity, and was oi the “dipping electrode” type for dilute solutions as furnished by Eimer and Amend. It n-as standardized by means of 0.005 N potassium chloride solution, and showed a cell constant of 0.1222. Corrections were made in all cases for the conductivity of the distilled water from which the solutions were made up. Xeasurements were made according to the usual method of Kohlrausch. The slide-wire, furnished by Fritz Kohler, was carefully calibrated, and the resistances used had a guaranteed accuracy of a few tenths of one per cent. The electrically heated thermostat was operated throughout the investigation a t 30°, and was controlled by a vaporpressure thermoregulator, previously described by one of us,l which kept the bath constant within 0.01’. When a single conductivity measurement was to be made upon a solution, a portion of the solution was removed and placed in a thin-walled test tu& immersed in the bath. The conductivity cell was then dipped into the lest tube, and, after temperature equilibrium was reached, the bridge reading was taken. When a conductivity titration involving a number of measurements was made, 100 cc. of the unknown solution, diluted with distilled water to -700 cc., was placed in a spherical short-necked flask supplied with a three-hole stopper. Through this passed a stirring rod, the conductivity cell, arid the tip of a buret containing the reagent which was added in the desired amount. -2ftzr each addition of reagent from the buret the contents of the flask were stirred and allowed to attain the temperature of the bath before bridge readings were taken. I n addition the cell was raised and lowered several times during this interval so as to allow the solution between the electrodes to mix with the surrounding solution. The general principles underlying this and similar methods of physicochemical volumetry have been discussed in detail by P. Dutoit.* The apparatus used b>-him is essentially the same as the one herein described, except that we use a different form of cell, which cannot be affected by such operations as stirring, and addition of reagent.
’ ’TIITS ~OURXAI.,36, 71’ (1914’ ‘0
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