of Types in Chemistry. 21 



and two equivalents of pyrophosphoric acid, when heated with 

 a third equivalent of water, yield in like manner two of tribasic 

 phosphoric acid, 



2(PH 2 7 ) = [(PH 2 6 ) 2 2 ] + H 2 2 =2(PH 2 6 H)0 2 =2PH 3 8 . 



Gerhardt long since maintained that Ave cannot distinguish 

 between polybasic salts and what are railed subsalts, Avhich are 

 as truly neutral salts of a particular type. Thus the bibasic and 

 tribasic phosphates are to be looked upon as subsalts which 

 sustain the same relation to the monobasic phosphates that the 

 basic nitrates bear to the neutral nitrates. He succeeded in pre- 

 paring two crystalline subnitrates of lead and copper, having 

 the formulas NO 5 , M 2 2 , HO (tribasic), and NO 5 , M 4 O 4 , H 3 O 3 

 (quadri or heptabasic), both of which retain their water of com- 

 position at 392° P. The compounds of sulphuric acid are, — 1st. 

 the true monobasic sulphate, S 2 6 MO, corresponding to the 

 Nordhausen acid and the anhydrous bisulphates; 2nd. the 

 ordinary neutral sulphates, S 2 O 6 , M 2 O 2 ; 3rd. the so-called 

 disulphates, S 2 O 6 , M 4 O 4 , corresponding to the glacial acid den- 

 sity 1780 ; 4th. the type S 2 O 6 , M 6 O 6 , represented by tur- 

 peth mineral; and 5th. the so-called quadribasic sulphates, 

 S 2 6 M 8 O 8 . The copper salt of this type, according to Ger- 

 hardt, retains, moreover, 6 HO at 392° F.* 



Without counting the still more basic sulphates of zinc and 

 copper, described by Kane and Schindler, we have the following 

 salts, which, in accordance with "YVurtz's notation, correspond to 

 the annexed radicals : — 



1. Unibasic .... S 2 H0 7 =S 2 5 monatomic. 



2. Bibasic S 2 H 2 8 =S 2 4 diatomic. 



3. Quadribasic . . . S 2 H 4 10 =S 2 2 tetratomic. 



4. Sexbasic .... S 2 H 6 12 = S 2 hexatomic. 



5. Octobasic .... S 2 H 8 O l4 = S 2 -0 2 octatomic. 



It is easy to apply a similar reductio ad absurdum to the ra- 

 dical theory in the case of the oxychlorides and other basic salts, 

 and to show that the radicals of the dualists are often merely 

 algebraic expressions. (See further my remarks in the American 

 Journal of Science, vol. vii. pp. 402-404 f.) 



The above, which we conceive to be a simple statement of the 



* Gerhardt " On Salts," Journ. de Pharm. 1848, vol. xii. American 

 Journal of Science, vol. vi. p. 337. 



•J* Those who are familiar with chemical literature will remember an 

 amusing jeu d' esprit of Laurent's, in which he invited the attention of the 

 advocates of the radical theory to a newly invented electro-negative radical, 

 EurMzene (Comjjtes Rendus des Travaux de Chimie for 1850, pp. 251 ami 

 376). We observe a late writer in the 'Chemical News' (vol. i. p. 326) 

 proposing, as a new electro-negative radical, under the name of hydrine, 

 the peroxide of hydrogen, HO, the eurhizene of Laurent ! 



