March 2, 191 1] 



NATURE 



25 



cerning sick clubs, insurance against illness, and many of 

 those other schemes promoted by the German Government, 

 the importance of which is now being so fully realised in 

 other parts of the world, are to be on view. 



It is to be hoped that now the matter has been taken 

 up, those interested in British sanitary science and the 

 ■scientific aspects of hygiene generally, will spare no effort 

 to make the British exhibit, in part at least, worthy of 

 those great leaders of sanitary science who, shortly after 

 the middle of the last century, did so much, not only for 

 Great Britain, but also for other civilised countries. 



j THE RUSTING OF IRON. 



''I'lrHE problem of the atmospheric corrosion of metals is 

 1 ■*■ a very old one. So long ago as 1769, only three 

 , years after Cavendish had demonstrated the solubility of 

 I chalk and magnesia in water charged with "fixed air" 

 ' or carbonic anhydride, it was shown by T. Lane, an 



apothecary of the City of London, that " water impreg- 

 ; nated with fixed air will dissolve a considerable quantity 



of iron, and thereby become a strong chalybeate " 

 J (Priestley, "Experiments on Air," 1772). Lane ' records 

 . (Phil. Trans., 1869, 1., 218) that " the clear water . . . 



■ decanted from the filings and ochrous sediment . . ., being 

 , exposed to the open air, presently threw up a party- 

 -coloured pellicle, and deposited a yellowish sediment." 



In this way the foundations were laid for the theory of 

 rusting put forward in 1888 by Crum Brown, according to 

 which the action consists essentially in the dissolution of 

 iron by carbonic acid, and subsequent precipitation from 



■ the solution of ferrous bicarbonate of ferric hydroxide 

 ' formed by the interaction of the ferrous salt with atmo- 

 spheric oxygen ; the separation of the rust is accompanied 

 by the liberation of the carbonic acid, which is thus set 

 free to attack a further quantity of iron. 



I The correctness of Crum Brown's theory was confirmed 



I by Moody's observation (Trans. Chem. Soc, 1906, Ixxxix., 

 720) that iron which had been cleaned with chromic acid 

 could be kept for long periods in contact with water and 

 air in a glass tube from which all traces of carbonic acid 

 were carefully excluded. Friend (Proc." Chem. Soc, 1910, 

 xxvi., 179) has confirmed this observation by condensing 



( Water distilled from an alkali upon an iron tube cooled 

 by circulating water. 



In a paper which has recently appeared in the Journal 

 of the Chemical Society, Messrs. Lambert and Thomson 



. have arrived at conclusions differing somewhat from those 

 of Moody and Friend. By electrolysing ferric chloride 



^ between electrodes of pure iridium foil, a specimen of iron 

 was obtained which gave a crystalline nitrate entirely free 

 from the violet colour which usually characterises this salt 

 and ordinary ferric alum ; the nitrate was transferred to 

 an iridium boat, ignited, and reduced in a stream of 

 hydrogen in a silica tube at 1000°. The metal thus 

 obtained (which appears to have been so pure as to be 

 acid-proof, like the redistilled zinc prepared some years 

 ago in Sir William Ramsay's laboratory) was found to be 

 unacted on by purified oxygen and purified water, but 

 when platinum vessels were used in preparing the iron, the 

 metal was found to be oxidised in the course of two or 

 three, hours, and a similar result was observed in the case 

 of commercial iron, whether it was cleaned with chromic 

 acid or not. 



The different results thus obtained mav very possibly be 

 attributed to a difference in the vessels 'in which the iron 

 was exposed to the action of water and oxvgen. The 

 dominant factor in promoting the atmospheric corrosion 

 of iron is undoubtedly carbonic acid, but there is no reason 

 to suppose that the part of the carbonic acid might not 

 be played by any other acid strong enough to act upon the 

 iron, though weak enough to be liberated by oxidation 

 from the ferrous to the ferric state. Silicic acid, the 

 immediate homologue of carbonic acid in the periodic 

 classification of the elements, might very possibly be cap- 

 able of producing a like effect, and, "if so, the use of 

 silica tubes would be likelv to promote rusting to a far 

 larger extent than tubes made of glass. The use of silica 

 tubes by Messrs. Lambert and Thomson in an experiment 

 in which one of the main objects was to eliminate acid 

 impurities is a change of which the advantn<res are very 

 questionable. The soluble (alkaline) matter dissolved out 

 NO. 2IS7, VOL. 861 



from ordinary glass does not suffice under normal con- 

 ditions to prevent rusting from taking place in glass- 

 vessels, but it is noteworthy that under the conditions of 

 Moody's experiments contact with the actual (acid ?> 

 surface of the glass was sufficient to cause the metal to 

 rust, whilst Friend has recorded a similar effect produce* 

 by particles of slag embedded in the iron. T. M. L. 



ECONOMIC GEOLOGY IN THE UNITED 

 STATES.^ 

 'T'HE three bulletins referred to below have been issued, 

 by the United States Geological Survey, which, at all 

 times keenly alive to the importance of economic geology 

 to the nation, has of late years been paying particular 

 attention to the study of the mineral resources of the 

 United States. The two first bulletins give an elaborate 

 and detailed account of the geology of one of the most 

 important oil-producing regions of central California. 

 Very little accurate geological work had been done here 

 previously, so that the present bulletins form a useful con- 

 tribution to general stratigraphical geology as well as to 

 the special geology of oil-bearing regions. There is 

 nothing that calls for particular notice in these bulletins ;: 

 the oil appears to occur in strata of the customary type 

 of Eocene, Lower and Middle Miocene age. Both reports 

 are elaborate and full of detail, and the report on the' 

 Coolinga district is noteworthy for the amount of 

 palasontological information that it contains and for the 

 admirable manner in which some of the fossils referred 

 to have been illustrated in the accompanying plates. 



The third of these bulletins deals with an entirely, 

 different subject, namely, the methods recently introduced 

 by the United States Government for the purpose of 

 placing its system of purchasing its coal supplies upon 

 a scientific basis. The method is roughly as follows : — 

 For each coal the moisture, ash, and calorific value (ex- 

 pressed in British thermal units) are determined upon 

 samples taken with all due precautions. The bids of 

 the various samples are sent in on ofificial sealed forms. 

 In order to compare these, all the tenders are reduced 

 to the same ash value by selecting as standard the coal 

 containing the lowest percentage of ash ; for each i per 

 cent, of ash above this figure, 2 cents per ton is added' 

 to the tender price. From this price thus adjusted, 

 and from the calorific power as determined, the cost 

 per 1,000,000 B.T.U. is calculated for each coal offered, 

 and as a general rule the contract is awarded to the 

 lowest cost as thus ascertained. As the heat value of 

 the coal is determined upon the coal as received, there 

 is no necessity to determine the percentage of moisture 

 that it contains. When a tender has been awarded to a 

 contractor, he is expected to maintain the quality of the 

 coal delivered at approximately the same standard as that 

 upon which the contract was awarded. For this purpose 

 careful samples are taken from each delivery ; when the 

 samples have been drawn, payment of go per cent, of the 

 amount of the account is made forthwith, the balance 

 being kept in hand until the samples are reported upon. 

 The price is corrected for variation in calorific power, by 

 multiplying by the number of B.T.U. in the sample and' 

 dividing by the number of B.T.U. upon which the con- 

 tract was based. Similarly for each i per cent, less of 

 ash in the sample of the coal delivered, a premium of 

 2 cents per ton is paid, and for each i per cent, of ash 

 more a deduction is made in accordance with a published' 

 schedule, an increase up to 2 per cent, of ash not being, 

 however, penalised. Of course the contract note contains 

 clauses under which a delivery containing an excessive 

 amount of ash, dust, or sulphur may be entirely rejected. 



It will be seen that this system of coal purchasing is 

 novel, and interesting to a wider public than that directly 

 concerned with the supply of coal to the various depart- 

 ments of the United States Government. H. L. 



' Department of the Interior. United States Geological Survey Bulletins. 

 (Washington, 1910.) 



(i) Geology and Oil Resoiirres of the Coolinga District, California. By- 

 Ralph Arnold and Robert Anflerson. Pp. ■^t;4. 



(2) Preliminary Report on the McKittrick-Snnset Oil Region, Peru, artf 

 San Luis Ohispo Counties, California. By Ralph Arnold and Harry R. 

 Johnson. Pp. 225. 



(i) The Purchase of Coal by the Government under ."Specifications ; witf> 

 Analyses of Coal delivered for the Fiscal Year 1908-9. By George S. Pope.. 

 Pp. 80. 



