Chemistry and Physics. 393 



corresponding salts which are not isomorphous." As examples, 

 the author notices that he was unable to completely separate 

 strontium chloride from calcium chloride, although the two salts, 

 separately, have an entirely distinct behavior when concentrated 

 hydrochloric acid is added to their solutions. On the other hand, 

 barium and strontium chlorides, although their behavior with 

 concentrated hydrochloric acid is similar, can be readily separated 

 so as to obtain pure barium chloride, because these salts are not 

 isomorphous. Calcium nitrate, having a crystalline form which 

 is distinct from that of barium and strontium nitrates, can be 

 separated from the latter. The sulphates of calcium, strontium 

 and barium are isomorphous, but although they differ considera- 

 bly in their solubility, for instance in dilute hydrochloric acid, 

 and in their stability towards the alkali-carbonates, it is never- 

 theless impossible to separate them when they are precipitated 

 together, and not each by itself. — Zeitschr. Anorg. Chem., xi, 

 305-378. h. l. w. 



4. A new class of compounds of metallic salts with ammonia. 

 — Wiede and Hofmann have described the salts C S 7 Co (NH 8 ) 6 , 

 CS 3 Ni(NH 3 ) s and C 2 S 7 Fe 2 (NH 3 ) 6 2H 2 0, which are evidently deriva- 

 tives of thiocarbonic acid, and members of a new class of the 

 interesting metallic-ammonia salts. The simplest method of pre- 

 paring the compounds is by the action of aqueous ammonia and 

 carbon disulphide upon the metallic hydroxides. The cobalt and 

 iron salts are black while the nickel compound has a ruby red 

 color, and all of them were obtained in a well crystallized condi- 

 tion. It is remarkable that iron forms such a compound. — Zeitschr. 

 Anorg. Chem., xi, 379. h. l. w. 



5. Influence of light on the form of discharge of a Holtz 

 machine. — Elster and Geitel have shown that the brush and 

 spark discharge of a Holtz machine, between a spherical anode 

 and a disc cathode, can be made to disappear under the influence 

 of ultra violet light. A concave disc of amalgamated sheet zinc 

 constitute the negative poles. When sparks are passing between 

 the sphere and the disc, they can be made to disappear by light- 

 ing a piece of magnesium ribbon in the neighborhood of the 

 cathode. When the magnesium light no longer illuminates the 

 cathode the sparks reappear. In this case the illumination 

 restricts apparently the discharge instead of increasing it. Elster 

 and Geitel return to the consideration of this phenomenon, and 

 conclude that the brush discharge and spark of a Holtz machine 

 is supplanted by a glow discharge when the cathode is illuminated, 

 and that this last form of discharge carries over a less quantity of 

 electricity than the brush and spark discharge in the dark. — Ann. 

 der Physik und Chemie, No. 3, pp. 401-407, 1896. j. t. 



6. Fluorescence of Vapors. — E. Wiedemann and G. C. Schmidt 

 state that sodium and potassium vapor fluoresce brightly, 

 the first green and the last red. The fluorescence spectrum of 

 sodium vapor gives continuous and also channelled bands, together 

 with the sodium line. Sodium and potassium vapor show also 



Am. Jour. Sci. — Fourth Series, Vol. I, No. 5. — May, 1896. 

 26 



