316 InieUi§ence and Misiitllaneotts Articles. 



thisiview yield afe folio\ys^:-428feO pidr/<jenbi|jho^pborio;aoidi':34*8i2 

 per centv protoxide oi laba^i I ii^ 9)lip«d cetSbjypeittaidtvkX noii, ^iaU 

 27'49 of water. /'uMin -ah iil .n')3f^ ^oiaoood Lafi I'ilrrrr sJi 



- ^'\iiviaiixte is isomorphous with cobalt blGom, the composition > of 

 which, according to Kersten, is = SCO, 2AsO,, + 8H0. Vivianite 

 is likewise in its origin 3FeO, PoO^ 4 8H0 ; but we ordinarily find 

 it only in pseudomorphous crystals,' -w^hich nevertheless possess all 

 the characters of genuine crystals, fbr' instance in their perfect clea- 

 vage. One portion of the protoxide has become more highly Oxidized, 

 and thus the blue colour of the mineral is produced, which is origin- 

 ally white, as is shown by the impure earthy varieties. Exactly tfiie 

 same takes place with the artificial proto phosphate of iron, which 

 passes more rapidly into the double salt of the protoxide from its 

 aggregated condition, and which exhibits the composition of vivianite, 

 except that it contains more peroxide. The formula of vivianite 

 should thus clearly illustrate what change has taken place in this 

 oxidation ; and this is exactly the case if the mineral contains 3 

 eq. of peroxide of iron, 18 eq. of protoxide of iron, 8 eq. of phos- 

 phoric acid, and 56 eq. of water. The quantity of water is the same 

 in both phosphates, and agrees exactly, with >th8iJ;^jpp;j^aipted.^,Jik^ 

 artificial salt. Oc 1)? 0*1 



Bearing these facts in mind, we arrive at '' ' q ''r 



6(3FeO,P2 0i-^8HO) + (3Fe,,03, ^P^OfiTf 8H0) 

 as the formula for vivianite ; and calculation according to this re- 

 quires 29'10 per cent, phosphoric acid, 33*00 protoxide of iron, 12'22 

 peroxide of iron, and 25 "68 water. Now as the artificially prepared 

 compound merely differs from vivianite in containing 2 eq. only of 

 the proto-salt, and perhaps this alone yields a blue compound, which 

 also exists in vivianite, its formula may be constructed thus : 

 4(3FeO,P20i + 8HO)4- 



[2(Fe3 03P20, -I- 8H0) + (SFcoOg, 2P0O3 + 8HO)] 



Thus we at once see how the perphosphate of iron, 3Fe203, 2P.^05 

 + 8H0, is formed from 3FeO 2P,,05 + 8HO. 2 eq. of the Iktter 

 have exchanged half the water for 3 eq. of oxygen, for '" '. ' 

 ^n^ q "SCSFeO, P.O3+8HO) = 6Fe 60 + 2P2 03 + 16Hd^'Y' 

 «[b.ari^?^93.2P,03-f 8H0 = 6Fe 90-f2P,03 + 8HO'„ (OHG ^ 

 omrt -^Idm diphosphate of the Proto- and Peroxide of Irony >""f'"^ "'^'* 

 It is well known that phosphate of soda, (2NaO, HO) Po r,, throws 

 down a white precipitate, which subsequently becomes blue, from a 

 solution of the protosalts of iron. If 1 eq. of phosphate of soda is 

 used to 2 of crystallized protosulphate of iron, the liquid separated 

 from the precipitate is colourless, but strongly acid, whilst the salt 

 of iron has a slightly acid reaction, and the salt of soda itself is pow- 

 erfully alkaline. It contains a considerable quantity of phosphoric 

 acid, as well as a small quantity of protoxide of iron ; hence the pre- 

 cipitate cannot, as has usually been considered, consist of 2FeO, 

 P2 Oj, but of 3FeO, PcjOj, and is thus analogous to the silver salt. 

 The precipitate quickly becomes blue on the filter ; when dried in the 



iiinorn 



