CHEMISTRY: E. C. FRANKLN

curvature on 0 and Ql correspond. Thus equations (7) and (11) definetransformations of surfaces Q of the Ribaucour type. We call themtransformations A. When in particular the surfaces C and C1 areassociate surfaces, which is a special case of transformations K, thesurfaces Co and Co1 are likewise associate, and the surfaces Q1 and ot,as defined in the preceding theorem, have the same spherical represen-tation of their lines of curvature.By means of a generalized theorem of permutability for transforma-

tions K in general we prove the following theorem of permutability fortransformations A: If 12 and %2 are two surfaces obtainedfrom a surfaceQ by transformations A, there exists a surface Q' which is in the relations oftransformations A with fi and %, and Q2' can befound without quadratures.

Isothermic surfaces are surfaces C for which t = 0. In this case the,transformations A are equivalent to the transformations Dm of iso-thermic surfaces, discovered by Darboux and studied at length by:Bianchi.3

Surfaces with isothermal representation of their lines of curvatureare surfaces Q in the sense that the surface C is the locus of the pointmidway between the centers of principal curvature of 0, and Co is atinfinity. This case requires special study, but the results are analogousto those of the general case. However, the transformations A are nowthe same as the transformations of these surfaces established fromanother point of view by me.4

'Eisenhart, Trans. Amer. Math. Soc. 15, 397-430 (1914).2Demoulin, Paris, C. R. Acad. Sci., 153, 703 (1911).a Bianchi, Annali Mat. Milano, Ser. 3, 11, 93-158 (1905).4Eisenhart, Trans. Amer. Math. Soc., 9, 149-177 (1908).

POTASSIUM AMMONO ARGENATE, BARATE, CALCIATE,AND SODATE

By Edward C. FranklinDEPARTMENT OF CHEMISTRY. STANFORD UNIVERSITY

Presented to the Academy. January 9, 1915

It has been shown by me that reactions strictly analogous to thosewhich accompany the solution of the hydroxides of zinc, lead, and alu-minium in aqueous solutions of potassium hydroxide take place whenthe amides of certain metals are treated with liquid-ammonia solutionsof potassium amide. Thus, just as zinc hydroxide is known to dissolvein an aqueous solution of potassium hydroxide to form potassium aquo-

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zincate, so potassium amide in liquid ammonia reacts with zinc amideto form potassium ammonozincate.1 These analogous reactions arerepresented by the equations:

Zn(OH)2 + 2KOH = Zn(OK)2 + H20,Zn(NH2)2 + 2KNH2 = Zn(NHK)2 + 2NH3.

In view of the many close analogies which have been shown to existbetween the derivatives of water and the derivatives of ammonia theformation of this potass'um ammonozincate and of potassium ammono-stannate2 and potassium ammonoplumbite' was not unexpected. Fur-ther work has, however, shown that elements which do not give rise tosimilar salts in water form these compounds in ammonia. Thus in pre-vious articles this was shown to be true of copper4 and thallium;6 andresearches have now been completed which show it to be true of silver,cadmium, and nickel. The work on silver will be here briefly described;that on cadmium and nickel, which was carried out by G. S. Bohart,will be later reported upon.Some years ago while studying the action of potassium amide on

liquid-ammonia solutions of silver salts6 it was observed that silveramide dissolves readily in an excess of potassium amide solution. Thissolubility recalled the amphoteric properties of the hydroxides of alumi-nium, zinc, and lead, and suggested that in all probability the solutionresulting from the action of a solution of potassium amide on silveramide would be found to contain an ammonoargentate of potassium.

It was found in fact that a crop of beautiful crystals of the compositionrepresented by the formula AgNHK.NH3 or AgNH2.KNH2 is obtainedwhen a liquid-ammonia solution prepared by dissolving silver amide inan excess of potassium amide is first adjusted to a proper concentrationand then cooled in a bath of liquid ammonia. After two or three re-crystallizations the salt is pure. The equation expressing its formationis AgNH2 + KNH2 = AgNHK + NH3. Because of the relationshipof the compound to the familiar (aquo) zincates and aluminates it isappropriately called potassium ammonoargentate.More surprising was the result of a later investigation7 in which the

amide of such a strongly electropositive element as magnesium was foundto react with potassium amide to form potassium ammonomagnesate,a compound of the formula Mg(NHK)2- 2NH3. This made it seem prob-able that potassium amide possesses the property of forming similarcompounds with the amides of all the metals. It was therefore deemedadvisable to study the action of solutions of potassium amide on the

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amides of the strongly electropositive barium, strontium, and calcium,and on the amide of sodium, in order to determine whether potassiumammonobarate, ammonostrontiate, and ammonocalciate, and possiblyeven potassium ammonosodate, can be prepared.When a barium salt in solution in liquid ammonia is added to a solu-

tion of potassium amide a microcrystalline precipitate is obtained whichhas been found to have the composition represented by the formula,BaNK. 2NH3.When solutions of strontium and calcium salts in liquid ammonia

are poured into an excess of a solution of potassium amide there areformed apparently noncrystalline products, which are representedrespectively by the formulas, SrNK.2NH3 and CaNK.2NH3. Thecalciate was also prepared by the action of potassium amide on metalliccalcium.When sodium amide is treated with a liquid-ammonia solution of

potassium amide, or when a solution of a soluble salt of sodium is addedto an excess of potassium amide in solution in liquid ammonia beautifulcrystals of a product whose composition is represented by the formulaNaNK2.2NHs, separate from the solution.For the reason that these compounds have been prepared by methods

entirely similar to those whereby potassium ammonomagnesate and theother salts of the same class mentioned above are formed they havereceived the names given in the title of this paper and are formulatedas salts with ammonia of crystallization. It is possible, however, toformulate them as molecular compounds of potassium amide with therespective amides of the less positive metals, as follows,Ba(NH2)2.KNH2, Sr(NH2)2.KNH2, Ca(NH2)2.2NH3, NaNH2.2NHK2;thus representing them as ammonia analogues of Werner's hydroxosalts.

It is hoped that transference measurements which are to be under-taken in this laboratory may show for such of these compounds as aresufficiently soluble whether or not the less positive metal travels togetherwith the nitrogen toward the anode during electrolysis.

1 Fitzgerald, J. Amer. Chem. Soc., 29, 657; Franklin, Ibid., 29, 1274 (1907).2 Fitzgerald, J. Amer. Chem. Soc., 29, 1693 (1907).Franklin, J. Phys. Chem., 15, 509 (1911).

4Franklin, J. Amer. Chem., Soc., 34,1501 (1912).s Franklin, J. Phys. Chem., 16, 682 (1912).Franklin, J. Amer. Chem. Soc., 27, 835 (1905).

7 Franklin, J. Amer. Chem. Soc., 34, 1455 (1913).

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