X-ferric oxide monohydrate ( /iFeOOH) and magnetite {?e-^0^ or Fe?0':<»FeO) 



Synthetic >^ferric oxide monohydrate is orange-yellovif in color as a powder, 

 and is identical, to the mineral lepidocrocite,^- It nay be dehydrated to 

 an anhydrous >- -form by heating to about 250°C, /t higher temperatures 

 the anhydrous form reverts to the.'<-oxide, as do other varieties. 



Since the >'-monohydrate is regarded as an intermediate substance in the 

 gradual oxidation of metallic iron to the final product, the o(.-raonohydrate , 

 sorae.-.'hat greater effort has been made to find a suitable way to form this 

 material in wood. This presents difficulties, because of inadequacies in 

 the basic knoviledge relative to the synthesis of this particular form. 



Fairly pure /-monohydrate can be made by oxidizing the precipitate formed 

 on the addition of pyridine to ferrous chloride, as described by Baudisch 

 and Albrecht (7), or by the oxidation of magnetite, '.hile these authors 

 ac!cnowled!7e that the ^'Iform can be made using certain other ferrous com- 

 pounds (1,10), they stated that, "... it ¥;as impossible to obtain the 

 X-hydrate from ferrous sulfate , , .," and, generally, describe the 

 essential condition under which the reaction ma^/ take yjlace as being depen- 

 dent on the tendency of the reactanta to form complexes. In our work v/e 

 havo found it nossible to obtain the ,V-form from ferrous sulfate, and have 

 made some study of the variations in the hydrogen ion concentration dui'lng 

 reaction periods and their influence on the ki.nd of reaction products 

 obtained. 



In general, vjhen a b-.sic substance is added to a ferrous salt, a while 

 film-like precipitate forms at first that degenerates to a green and 

 finally to a black material. -;hen this precipitate is oxidized usually a 

 mixture of the c(- and >--ferric oxide monohydrates is obtained. Prior to 

 oxidation, the suspended particles produce a higher pH value than that of 

 the surroundihg solution, which is primarily the excess of the ferrous 

 salt used, as shown by the data in Table 1, In using a glass electrode 

 pH meter, it vra,s found necessary to take very raioid readings in order to 

 obtain meaningful values because these suspended particles tended to col- 

 lect rapidly on the surface ox the electrodes causing an ir.struTiental drift 

 and thus yielding values other than an "average" pH for the trv.e solution 

 plus the colloidal phase. The electrodes v/ere rinsed betwc-e-.: ga'-h measure- 

 ment to eliminate any accumulative chan£;e. .fliile this did not rt^.Tove adher- 

 ing particles, it apparently allowed the film to ox-idi2e, so as not to 

 affect the calibration of the instr-oment. The reprocucibi] it.y oi the values 

 obtained vrith this procedure v/as within t'le approximate linits of 0,1 ph. 

 In the aijove tests it vras observed that after the addition of sodium hydrox- 

 ide to a ferrous sulfate solution the pH did not imnediately assume a con- 

 stant value. The initial reading was the highest value attained from which 

 successive readings rould gradually decrease. Table 2 shows the changes in 

 pH when 7,5 cc. of IM. sodium hydroxide were added to 100 cc. of 0.5 M, 

 ferrous sulfate, ith air bubbling through the solution to cause oxidation 



Lepidocrocite is a pleochroic mineral exhibiting several colors, depending 

 on the surface viewed. Naturally-occurring crystals .vhich are probably 

 larger appear as blood red (7). 



