July 6, 1900.] 



SCIENCE. 



29 



it lias been very meagerly worked out for 

 the eighth group. In the case of platinum 

 both potassium plato- and platithiocya- 

 nates, K.PtCSCN), and K,Pt(SC]Sr)„ are 

 known, and are salts of the plato- and 

 platithiocyanic acids. These are complex 

 acids and may be separated out, but in the 

 free state are very unstable. The double 

 ferric thiocyanates may be formed but there 

 is no corresponding complex acid, that is, 

 they are ordinary double salts. The fer- 

 rous, cobaltous, and nickel thiocyanates are 

 known, but form no double salts. It is 

 extremely probable that the other metals 

 of this group would show a full series of 

 thiocyanates. 



Another interesting class of complex 

 salts is that of the double nitrites, first 

 studied in the case of platinum by ISTilson, 

 but for the other platinum metals by Wol- 

 cott Gibbs, who bases upon these his 

 method of separating the metals. More 

 recently these nitrites have been investi- 

 gated by Joly, Vezes, and Leidie. The 

 most familiar double nitrite is the potas- 

 sium cobaltinitrite, which has long served 

 for the separation of cobalt from nickel, 

 and which is also used as a pigment under 

 the name of aureolin or cobalt-yellow. 

 These nitrites resemble, to a considerable 

 degree, the double cyanids, and in the 

 case of iridium the free complex iridoni- 

 trous acid has been obtained. In the case 

 of iron, cobalt, and nickel, we have also 

 representatives of a large class of very 

 staple triple nitrites, first noted by Klinzel 

 and Lang and studied by Erdmann.* More 

 recently these have been investigated by 

 Przibillaf who, after great difiiculty, suc- 

 ceeded in preparing the triple iron potas- 

 sium nitrites with lead, barium, strontium, 

 and calcium ; this is the first nitrite of iron 

 to be prepared and leaves osmium as the 



*J.praM. Chem. 97, 385 (1886). 



i Ztschr. anorg. Chem., 15, 419 (1897). 



only metal of the eighth group of which 

 no nitrite is known. 



In the case of all platinum metals double 

 sulfites are known, which are salts of com- 

 plex metallo-sulfurous acid. In these metals 

 the presence of the sulfurous acid radical 

 cannot be detected by ordinary reagents. 

 In the case of cobalt, a full series of cobal- 

 tisulfites is known, which are stable salts, 

 while the cobaltosulfites are very unstable. 

 Little is known of iron and nickel sulfites, 

 and there is much room for further inves- 

 tigation in the case of the sulfites of the 

 other elements of this group. There is at 

 the same time reason to believe that a study 

 of the thiosulfates and possibly the dithio- 

 nates of this group would not be without 

 interest. 



Another acid which is capable of form- 

 ing complex salts is oxalic. The platoxal- 

 ates are the only ones which have been 

 carefully studied, though some work has 

 been done upon the rhodoxalates. Several 

 iron oxalates and double oxalates are 

 known, but aside from this the field is 

 nnworked but promising. In this connec- 

 tion it may be added that while oxalic acid 

 is the only organic acid which has been 

 investigated to any considerable extent in 

 complex salts, it by no means follows that 

 it is the only acid which is capable of enter- 

 ing into such combinations. Some of my 

 students have made preliminary tests with 

 a large series of acids and found that sev- 

 eral among them enter combination with 

 chromium with the formation of complex 

 salts, and it is quite possible that similar 

 compounds may be formed with the eighth- 

 group metals. Mention should also be 

 made that Gibbs has introduced platinum 

 into his complex salts, forming platinimo- 

 lybdates and platinitungstates. 



Since complex salts of hydrocyanic, ni- 

 trous, sulfurous, oxalic, and other analo- 

 gous acids are best developed generally with 

 the metals of this group, it is in the study 



