410 Mr. R. Phillips's Ohse^'vations 



cessary a like change in the received atomic weight of sodium, 

 with the oxide of which in anhydrous sulphate of soda (The- 

 nardite) that of silver in sulphate of silver is isomorphous. 

 Soda, common salt, and sulphuret of sodium must be repre- 

 sented Na, NaCl, Na N." " Nor," says Professor Johnston, 

 " can the change stop here." Indeed I wish he could point out 

 where it will. " Several years," he continues, "have elapsed" 

 since Mitscherlich announced the very interesting fact, that the 

 nitrates of potash and soda were isomorphous respectively with 

 arragonite and calc spar, and that they presented the same 

 cleavages (Pogg., ^w.,xviii. p. 173) ; to which Marx afterwards 

 added that the rhomboids of nitrate of soda possessed the doubly 

 refracting structure in a higher degree even than calc spar. 

 {Jahrhuch der Chim, und P/ii/s.,xix. p. 166.) From these obser- 

 vations it was natural to infer that some relation existed be- 

 tween the two alkaline nitrates analogous to the relation be- 

 tween the two forms of carbonate of lime ; that like carbonate 

 of lime the nitrates of potash and soda might each be capable 

 of assuming two forms isomorphous each with each, though 

 in ordinary circumstances of temperature, &c. the form pre- 

 ferred by each did not correspond ; the nitrate of potash ge- 

 nerally affecting the right rhombic prism, the nitrate of soda 

 the rhomboidal form. The probability of such a relation was 

 strengthened by a comparison of the analysis of chabasie from 

 different localities and by different chemists, from which there 

 appeared strong reason for believing that potash and soda were 

 capable of replacing each other in equivalent proportions." 



I wish Professor Johnston had favoured us with the ana- 

 lyses from which he has arrived at the fore-mentioned conclu- 

 sion. 



I have copied all I can find ; they amount to seven. 



*1. 2. 3. 4. 5. 6. 7. 



Silica 43-33 50-65 49'17 4907 48756 48-988 46184 



Alumina .... 22-66 17-00 18-90 18-90 17'440 19774 18-423 



Lime 3*34 9-73 10-463 4-068 7029 



Potash 9-34 1-70 ... 1219 1-458 



Soda 12-19 6-066 5967 



Oxide of iron ... 0404 0397 



Water 21- 19-50 19-73 19-73 21720 20-700 22- 



99-67 . 98-58 : 99-99 : 9989 : 99842 . 100- 100- 



I confess I am entirely at a loss to conjecture on what prin- 

 ciple Professor Johnston finds " strong reason" for believing, 



• 1. Vauquelin. 4. Arfwedson. 7. Lehunt. 



2. Berzelius. 5. Dr. Thomson. 



3. Ditto. 6. Lehunt. 



