COJIJIUXICATIOKS TO THE EDITOR THE OSID,ITIOS OF FERROCS SULFITE IS AIR Samples of ferrous sulfite were obtained by mixing ferrous sulfate and sodium d h t e aolutions in a hydrogen atmosphere; they were creamy i r h i t e precipitates ind ivere nashed with air-free itater and alcohol and then dried in a vacuiim lesiccator over sulfuric acid. These precipitates became more or less dark on he surface, owing to unavoidable short contact I\ ith the air; nhen dry, they were :ream to various shades of bra\\ 11. L-nder the microscope they were seen to con,ist of colorless or pale greenish yellon- crystals n ith a coat of yellow-bronn xidized material; this latter n-as sometimes of a cauliflon er-like growth from he crystals. T h e n dry, the samples were exposed to air in a large desiccator containing calcium chloride which was opened only occasionally; or they 11 ere txposed to the air in a balance case containing some sulfuric acid, but this rase vas opened more often to the air. These samples \\-ere analyzed from time to imp over a period of years. The per cent of ferrous sulfite fell regularly and coninuously, often slowly at the rate of about 0.4 per cent per year, but sometimes nuch more quickly, even up to 2; or 50 per cent per year. The purer and the Irier the original sample, the slower is the subsequent oxidation. If the original ample is moist or contains much disseminated oxidation product (iron hydrosh?), then the subsequent oxidation is more rapid. The analysis of the ferrous sulfite presents some difficulties. By placing a eighed sample in an excess of standard potassium dichromate solution plus ydrochloric acid, the oxidation is rapidly completed to ferric sulfate, and the
excess of tlichromute is found by using an escwa of standard ferrous chloride solution and finishing ji-itli dichromate titrat,ion. This method gives concordant results; duplicates difi'er by less t'han 0.5 per cent, ferrous sulfite; it estimates, of course, the combined ferrous and sulfite radicals, jvhich are calculated as FeSOa. The use of potassium permanganate, instead of dichromat,e, gives low results for ferrous sulfite, t'he usual oxidattion of sulfit,e to ot8herthan sulfate then occurring. Test's .with sodium sulfite indicated that the above dichromate method gave higher results than the iodine method used in the same manner; e.g., 84.9 per cent sodium sulfitc ~ ~ found a s by t'he dichromate method and 83.8 per cent by the iodine method. Of course t,he per cent' of ferrous sulfite found in the ferrous sulfite samples by t,he dichromate method T\-ill be high if the samples contain ferrous hydroxide, etc. In the final solutions from t,liese assays the sulfat'e x a s determined as barium sulfate. The sulfate due to t,he oxidat'ioii of t8hesulfite was calculat'ed, and then by subtracting this from t'he t'otal sulfate found, the original sulfat,ein the sample \vas found. In many cases during t'he oxidation of the ferrous sulfites the gain of sulfate was equivalent to t'he ferrous sulfite loss, but sometimes t'his was not observed or was obscured by the greater experimental error accumulating in the sulfate determinat'ion. Tlie fresh samples of ferrous sulfite showed a sulfate value less than that equivalent8t o the ferrous sulfite content : the latter value therefore was high due to ferrous hydroxide, etc. This deficiency of sulfate mlue (up to 3 per cent at the start j cut out in about i 0 days; any ferrous hydroxide in the samples is thus oxidized faster than the ferrous sulfite. -1set of four samples of ferrous sulfite was made by placing tiolid ferrous sulfate iiid sodium sulfite crystals and water in tnbes which n-ere then sealed. On solution and mixing, IiufT t o browi prccipitates appeared. After seven years t'he solutions \\-ere colorless or brownish over cream n-hite pori-ders; the latter were Trashed J\-ith \I-ater and alcohol and were dried over sulfuric acid in z'ucuo for from 1 t u 'T days. In tn-o of the tubes a crust, of ferrous sulfite had separateci; these \\-ere ivashcd and dried as before, apart from the loose precipitates above; this bullied sample vas the purest sample of ferrous sulfite obt.ained. This sample \vas kept in a sniall iveighing h t l e , generally closed, in t'he balance case; it cont,ained i0.3 per cent' ferrous sulfite a t the start and 69.3 per cent ferrous sulfite a year later. *\not81ierof t'hese samples decreased from 69.9 to 63.4 per cent ferrous sulfite in a year, this sample being open continuously in the balance case and occasionally stirred up : the t'wo other samples were kept in the same manner, and the average loss of ferrous sulfite in a year was i per cent. The first sample in the lveighing bottle \\-as analyzed seven times over the year; the mean values of the last six analyses were: per cent FeS03 = 69.6 (E 49.1 per cent SO4 and 28.6 per cent ferrous Fe); per cent SO4 (total) = 49.3; per cent so4 (free) = 0.4; per cent ferrous Fe (direct) = 28.6; per cent total F e (direct) = 29.0. It would therefore contain 97.3 per cent FeS03.3H20plus 2.7 per cent (or probably less) of iron hydroxides. (FeS03.3H20contains 71.6 per cent8FeS03, 29.4 per cent ferrous Fe, and ivould give equivalent so4 = 50.5 per cent.) Of the samples of ferrous sulfit'e kept in the calcium chloride desiccator one
decreased regularly from 68.2 t o 64.9 per cent ferrous sulfite in 91 months, i.e., untlel*\\-enta loss of 0.36 per cent ferrous sulfite in a year; tn-o other samples beliavetl similarly. T T Ysamples ~ u-ere kept for some months in the desiccator, then \yere sealed in a tube for six years, then \\-ere exposed again to the air in the balance case, when the oxidation (which had ceased in the sealed tube) again became very rapid; one of these samples shoved the follon-ing time and aizalysis results: 0 (start), 60.3 per cent FeSO3; 6 months, 46.3 per cent FeSO;; t'hen sealed until Sti months, -48.0 per cent FeSO;; thereafter open, at 91 months, 26 per cent, FeSOs; a t 97 months, S.5 per cent FeSOZ. This sample had much red-bra\\-n iron hydroxide mixed n-ith it from the start, and t'hat oxide or t'hat disseminated form of ferrous sulfite quickened the oxidation; this sample shoived t'he most rapid oxidation of all the samples of ferrous sulfite. But pure dry crystals of FeSOa 3H20 evidently oxidize very slo\\-ly (and dehydrate very slowly) under ortlinu ry c untli ti 011s.
JAMES R.POVSD. The $c~hoolof Xines Ballarat Tictoria, -k.ustmralia Xox-eniber 29, 1947
It i* \\ell knon n that aluminum inimci+ed in
d u t i o n of certain aluminum This property is taken ntlvnntage of for rectifying the current. and the ti-ual explanation given for this phenomenon i,- that the pa*,-age of the cuirent i- prcvented by thc formation of a hlm of oxide. ( ' c i ~ a i nfactb h a w comP t o my attention nhich indicate that theie are other facto15 uhich may he rey~onsihlefor thiq pcculiarity of aluminum and of other metals. I n elect]olyzing an aluminum wlfate bolution ivith a platinum anode, an aluminum strip n-as inserted into the anode compartment. The solution n-as hot, and the strip of aluminum dissolved Jrith energetic evolution of gas. The strip of aluminum n a s then connected to the platinum anode and the evolution of gas stopped, or very nearly so. On breaking the connection v-ith the platinum anodt the evolution of gas reappeared instantaneously. The fact that these effectb are observed at once does not seem to 3upport the theory of an oxide film, hecatuse its formation and disappearance must take time. The film of oxide can be a contributing factor, but it cannot be solely responsible for the obstriiction of the current. The idea came to mind that it may be due t o borne special electronic structure, such that electrons under the electrical held can move only in one direction and not in the other. :I
d t . doe. not conduct nnodically, or doe- *o T-ery poorly
