( 357 ) 



the (.YZ/J between the llh and the Cs, is in tliese respects less 

 correct than in tlie [)roxiinity of the 77. 



That however, as soon as we consider llie i,n-cal iiiiinhc>r of facts 

 wiiich have been collected by other investigators besides Tltton, — 

 but little is left of these sni)posed general rules may I)c seen from 

 a short recapitulation : 



1. The ncld tartrate.^ of K, llh, C.s, .V//, and 77 aic rhombo- 

 bisphenoidic and form an isomorphous series. In this the /^t» and the 

 TZ-salt are placed the nearest to each other, then follows the (A7/ )- 

 salt, the A^-salt and tinally the ^,!s--salt. 



2. On the other hand, the Rh- and CVsalts of the neiitntl 

 tartrates are trigonal ; the 7V-salt is monoclinic and trigonal, whereas 

 the (N'H.yssdt, although also monoclinic with comparable parameters, 

 is certainly 'not isomorphous with the monoclinic form of the 7y-salt. 



In connection with the following it should be observed that with 

 the T/-salt the angle /■? = 86°43'; with the (A^//J-salt, ji = 87°37'. 



3. Now, proceeding to the complete series, which are related to 

 inorganic acids, we may mention here, besides the sulphates, sele- 

 nates and double sulphates investigated by Tltton, the K-, {N H^)-, 

 Rb-, Cs- and Tl-ahuns, derived from aluminium (Pettersson), those 

 froui vanadium (Piccini) and clirumiuin, those from (jaUium and 

 iron (Sorret). those from rhodium, indium and iridium. There is 

 here nowhere any indication of polymorphism, but with the oi'dinarv 

 alums for instance a quite regular moditication of the physical pro- 

 perties has been noticed, which gives no occasion to assign to the 

 (iV^i/J-salt a particular position in the series. 



4. Of the chlorates the A'-, Rh- and C!y-salt are probably isomor- 

 phous ; the 7V-salt is isodimorphous and has one foi'm which is 

 isomorphous with the /v-salt ; the (.V/f/)-salt, however, is trigonal- 

 pseudo-cubic, like Kd>romate. The latter is isodimorphous with 

 /f-c hi orate. 



5. In the series of the pcrchloi'tili's which is i.«omorplioiis, the 

 77 is also placed nearest to the Rh. 



6. K-iJdr.^ulphate: ^.^^.^0^ is triclinic-pinacoidal : the Rh-, Cs-, 

 (xV //,)^ and 77-salts are monoclinic and isomorphous. Here we have, 

 therefore, an isodimorphous series. 



7. The K- and Rh-jdnlinuiii-iiitrites are monoclinic; ^ \-philiniini- 

 nitrite is also monoclinic, but totally dilfers from the two others ; 

 tinally, the 7V-salt is again monoclinic but still again dillerent from 

 all other salts, so that we have here a xavy interesting case indeed 

 of an isotriuiorplious series. 



Of the same compounds, but crystallising with 2 //./>, I he A'-sall 



