946 



SCIENCE. 



[N. S. Vol. VIII. No. 209. 



in which they give up their water of crys- 

 tallization. A typical example is copper 

 sulfate, which not only forms the compounds, 

 CuSO,, 5H„0 and CuSO,, 5NH„, but also 

 the four intermediate compounds, CuSO^, 

 4H,0, NH3 ; CuSO,, 3Hp, 2NH3 ; CuSO,, 

 2H,0, 3NH3 and CuSO,, H^, 4NH3, so 

 that the replacement of water by ammonia 

 is not a mere figure of speech. In the last 

 number of the Zeitsdirift fiir anorganisclie 

 Chemie, Fritz Reitzenstein takes up the re- 

 placement of water by other nitrogen bases, 

 especially pyridin, and shows that a large 

 number of salts form similar compounds 

 with pyridin, as with water of crystalliza- 

 tion. Some of these were known before, 

 but twenty-eight new ones are described, as 

 well as several compounds in which quino- 

 lin replaces the water of crystallization. A 

 table is appended to his paper giving several 

 hundred of the known hydrates, ammonia 

 compounds and pyridin compounds in jux- 

 taposition, and the resemblance of the tyj)- 

 ical members of each group is striking. 



In the previous number of the Zeitsdirift, 

 Eeitzenstein's ' Habilitationschrift ' is pub- 

 lished, which is a very complete history of 

 the different theories of the constitution of 

 the metal- ammonia salts. The first notices 

 of the combinations of certain salts with 

 ammonia date back to Bergman and Tas- 

 saert in the last century, but no particular 

 attention was attracted to them until the dis- 

 covery of the first platinum-ammonia com- 

 pound by Magnus in 1828. This was 

 quickly followed by the preparation of new 

 platinum bases by Gros (1838), Reiset(1840- 

 1844), Peyrone (1844), Eaewsky (1847) 

 and Gerhardt (1850). As early as 1841 

 Berzelius attempted to explain their consti- 

 tution according to his general theory of 

 salts, but Clans was the first who held the 

 view accepted to-daj' that the ammonia is 

 present in the compound as the ISTHg group. 

 This was brought into accord with the 

 valence theory by Jorgensen, of Copen- 



hagen, who has been the most prolific 

 worker in the metal-ammonia compounds, 

 and until recently his views, which repre- 

 sent the ammonia groups as united with 

 each other, as — NH, — NH3 — NH^ — NH, 

 — , has been generally accepted. Here the 

 ammonia is often replaced by water, in 

 which case the oxygen is looked upon as 

 quadrivalent. In some series, as among the 

 platinum and cobalt bases, isomers are met 

 with, and some of them are difficult to ac- 

 count for by Jorgensen's theory. Within the 

 present decade Alfred Werner, of Zurich, 

 has proposed a new theory, which repre- 

 sents the atom of the metal as in the center 

 of an octahedron, surrounded by six other 

 atoms or groups (as NH3 or H„0), one at 

 each angle. In some cases there are bat 

 four attached atoms or groups, in which case 

 the configuration can be represented as on 

 a plane with the metal atom in the center 

 of a square and one group at each of the 

 four angles. This complex is supposed to 

 have a certain amount of combining power 

 as a whole, and unites with negative or 

 positive elements to form salts. Werner 

 carries this theory out in application to 

 many other classes of salts, as, for exam- 

 ple, sulfuric acid, where the complex SO^ 

 is united with two atoms of hydrogen ; po- 

 tassium permanganate, where the complex 

 MnOj is united to one atom of potassium ; 

 (HgClJK,, (PtCl,)K„ (SiFJK,, etc. The 

 idea of valence is not wholly abandoned, 

 but is not adhered to in the formation of 

 the complex. The theory is too new to 

 prophesy whether it will meet with general 

 acceptance, but in its application to the 

 platinum and cobalt bases it explains much 

 that is difficult to account for on the valence 

 theorj' as ordinarily accepted. Reitzen- 

 stein's paper and recent papers by Werner 

 should be consulted for the full explanation 

 of the theory. 



In this connection it may be noted that 

 the resemblance of water to ammonia is not 



