of the Elements. 433 



comjDOunds of HN or ]\IN, which in their formulfe and proper- 

 ties correspond very closely with the oxidized compounds of HCl 

 or MCI. Thus we have, — 



Chlorite of potash . K ClO^ I K NO^ Nitrite of potash. 

 Chlorate of potash . K ClO^ | K NO^ Nitrate of potash. 



Moreover N^ 0'* corresponds closely with CP O'*. 

 It is interesting to contrast the parallel compounds to which 

 chlorine, sulphur, and phosphorus respectively give origin. 



Bibasic series. 



Monobasic series. 



HCl Chlorhydric 



acid. 

 HCIO H3pochlorous 



acid. 

 HC103 Chlorous acid. 



HCIO^ Chloric acid. 



HC10» Perchloric acid, 



Sulphydric 



acid. 

 Et^TO Oxide of tel- 



lurethyle. 

 CP SO- OxychloVide of 



sulphur. 

 H" SO"* Sulphurous 



acid. 

 H^ SO* Sulphuric acid. 



Tribasic series. 

 H^P Phosphaniine. 



CP PO Oxychloride of 

 phosphorus. 



JJ3 PQ2 Hypopliospho- 

 rous acid. 



JJ3 PQ3 Phosphorous 

 acid. 



H^PO'' Phosphoric acid. 



We have seen that the simple atom of sulphate of potash, 

 K^ SO"*, may be represented as consisting of oxide of potassium 

 united with sulphuric anhydride, K'^'O . SO^. The double atoms 

 of monobasic and terbasic salts may be represented in a similar 

 manner ; and doubling the atom of the bibasic salt for the sake 

 of analogy, we have the following sequence : — 



2KI04 = K^O.PO^ . . Periodate of potash. 

 2K2S04= 2K20.S2 0« . . Sulphate of potash. 

 2K3P04= 3K20.P2 05 . . Phosphate of potash. 



The corresponding formulae for the chromates and iodates will 

 be— 



2KI03 = K^O . P 0^ 

 2K2Cr2 04 = 2K20.Cr4 0«. 



Now there are certain salts, mono-, bi- and ter-basic, in which 

 the ratio of oxide to anhydride differs from the above normal 

 proportion. The salts with an excess of oxide are termed basic 

 salts ; the salts with an excess of anhydride, anhydrosalts. As 

 instances of anhydrosalts, we have — 



The above symbols are most expressive of the correlations of 

 the different salts, though simpler formulae arc preferable for 

 general use, Thus — 



