two articles have appeared by Bichsel on electron microscopy ; one is concerned with an investigation of sub-grain structure in high purity aluminium , while the other is general , describing the application of oxide replica techniques and the examination of thin foils . the illustrations in all these papers are impressive scientifically and attractive aesthetically ; it is only a matter of time before they receive the attention of designers of wallpaper , floor coverings and similar goods . single crystals continue to attract the experimenter ; McKinnon has studied the work-hardening of a super-purity aluminium crystal , and indicated that during stage 1 , that is the period of slip on ( 111 ) plane of maximum resolved shear stress , the rate of hardening is determined by the amount and type of uniformly distributed secondary slip . Greetham and Honeycombe have deformed single crystals of aluminium-4.5 % copper given various ageing treatments after solution treatment . under-aged crystals showed a marked yield point followed by a period of low hardening , while over-aged crystals and those treated at the optimum temperature , though showing no yield point , strain-hardened rapidly . by X-ray and metallographic study , Richards and Pugh have determined the sequences of behaviour of super-purity aluminium during rolling and annealing . structures after various amounts of cold reduction are illustrated as photomicrographs and X-ray transmission patterns . Blade , Clare and Lamb have used levitation melting to provide ingots of zone-refined aluminium containing additions of various elements , which were then rolled to sheet for determination of recrystallisation temperatures . as little as 0.001 at % of the addition elements was sufficient to produce most of the retardation of recrystallisation ; silicon , copper and magnesium each caused an increase of recrystallisation temperature of 50-100 &amp;deg; C , while for iron , chromium and manganese a figure of c 200 &amp;deg; C is quoted . at temperatures varying from 195-500 &amp;deg; C , Ormerod and Tegart have subjected super-purity aluminium to torsion stresses , and determined torque values which are converted to shear stress , while specimen revolutions are converted to shear strain , the two being used to draw true stress &amp;sol; strain curves . Davies has performed stress-rupture tests on the aluminium-1 % nickel alloy favoured for resistance to corrosion by high temperature water , and obtained 1,000 hour values of 0.75 at 350 &amp;deg; C , 1.8 at 250 &amp;deg; C , and 4.2 at 100 &amp;deg; C , the units being kg &amp;sol; sq mm ; English eyes would have preferred tons &amp;sol; sq in . corrosion and protection . no form of degeneration of metals is more insidious than corrosion , and the volume of work published on the subject is a measure of the seriousness with which it is viewed . Evans has produced a monumental volume of great authority on the corrosion and oxidation of metals in general , with an author index containing no less than 3,000 names . a fat volume , but the scribbling has been very well worth while , and as with Gibbon &apos;s work it will well outlive the author . another useful book is that written by Rogers , principally for the education of naval constructors who are responsible for the maintenance of ships of war ; aluminium receives its due meed of attention , with alarming illustrations of what happens when wrong procedures are adopted , and details of correct design and practice . the power of the corrosive enemy must be recognised and assessed ; Great Britain has the unenviable reputation of being a particularly aggressive place . Ambler has found that the distribution of chloride in the British atmosphere has the same general relation to distance from the sea as in west Africa , and that the corrosion of steel and zinc bears no relation to salinity ; encouragingly , he considers that the corrosion of his aluminium specimens was so small as to give high errors on cleaning . a new hazard has been added to corrosion testing . at Llanrhystyd , Ambler &apos;s specimens were liable to be licked by cows on the landward side ; he states that this would not be expected to give low results , but this surely depends on the corrosivity of cow saliva as against the beneficial effects of regular cleaning . in continuing its work on the basic causes and mechanism of corrosion , the national bureau of standards in the U.S.A has established that with large single crystals of high purity aluminium exposed to an acid mixture , configuration of etch pits differed according to crystallographic orientation , and the rates of attack varied radically from those observed in an alkali mixture . Edeleanu has studied the pitting mechanism , using 99.999 % aluminium foil in sodium chloride solution , and demonstrated that the rate of attack per unit of active area inside a pit is a constant , and that changes in an external polarising current change the rate of pitting only by altering the active area . an electron micrograph of a pitting system illustrates effectively the frequent changes in direction of the attack . in a general summary of the causes of pitting and its effects , Robinson makes the cardinal point that to avoid it one must eliminate the chloride ion or inhibit it ; it is not always possible to adopt either of these admirable actions , so that pitting must sometimes be lived with and allowed for in design and selection of materials . susceptibility to intercrystalline corrosion may be a less serious matter than proneness to stress-corrosion ; indeed , in the high strength Al-Zn-Mg-Cu alloys , stress-corrosion failure can occur when very little evidence of corrosive attack is to be detected . in developing tests for the susceptibility of this type of alloy to intercrystalline attack , Ketcham and Taylor do not mention stress-corrosion , and while their tests are no doubt of value , tests including stress application would be preferred . silver is highly cathodic to aluminium , and alloys containing large additions of silver might be expected to be correspondingly low in corrosion resistance . this has been shown to be the case by Stadelmeier and Whitener ; in their aluminium-silver alloy , Ag2Al was precipitated on the grain boundaries , and in a refrigerator atmosphere samples were completely pulverised in four weeks . a committee of the national association of corrosion engineers has reported on its investigations of techniques applicable to the examination of aluminium corrosion products , including X-ray diffraction and fluorescence , thermal analysis , electrographic methods , spectrographic analysis , microscopic examination and quantitative and qualitative tests . having purified water sufficiently for it to merit the application high-purity , the user is anxious to keep it so , and Knoedler and Gordon have assembled test data on many materials that may be used for containers , pipes , etc , including steel sprayed with aluminium , and the same combination coated with a polyvinyl top coat . commercially pure aluminium and aluminium-manganese alloy tanks were also used , and the water showed 0.035 parts per million of aluminium after 56 days &apos; storage ; a very low proportion . in comparing metals for compatibility with 90 % hydrogen peroxide , Bloom and his co-workers award classification 1 only to pure aluminium , certain aluminium alloys and zirconium . a rocket fuel rejoicing in the name of unsymmetrical dimethylhydrazine has been successfully stored in aluminium containers for three years without ill effect , as reported by Raleigh and Derr . many somewhat unusual chemicals are needed in conjunction with rocket engines , and Geiger , Schuler and Mowers have discussed material selection problems in the light of present knowledge . aluminium is compatible with hydrogen peroxide , nitrogen tetroxide , liquid fluorine and inhibited red fuming nitric acid , amongst other rocket chemicals . Aylmore , Gregg and Jepson have studied the oxides formed when aluminium is heated in dry oxygen and interpreted their results as showing crystallisation of an initially formed amorphous layer . using an A.C bridge , Lorking measured the capacity and thus the thickness of non-porous oxide films on aluminium ; chloride ions in solution increased the permeability of the film , and this was detected by potential measurements . since a general air of pessimism permeates the account by Capp and Philibert about ship corrosion , their remarks about trouble with aluminium are perhaps less unacceptable ; however , they seem to be ill-informed about developments since the war in such matters as riveting and boundary bar joints , and the general avoidance of bimetallic corrosion . the stupid things that are still done are exemplified in an account by Brooks of a floodlight from a fishing vessel , that had castings in an aluminium alloy containing 2 1/2 % copper , was bolted together with brass bolts , and employed an absorbent fibre gasket . it seems hardly conceivable , but these things still happen , even in the second half of the twentieth century . in the aircraft industry , hazards are much more fully recognised ; Heath has shown how modern aircraft design is being modified to provide access to all parts for inspection , to ensure that unobserved corrosion can not proceed to cause a catastrophe . this requirement in design is , of course , most important in modern aircraft from which long service lives are expected . corrosion at welds has not proved a serious problem with aluminium since the dangers of flux entrapment were eliminated by the adoption of inert gas-shielded welding methods ; however , trouble with large gas-welded cooking pans in aluminium-2 % magnesium alloy described by Latimer was not due to flux residues . knife-edge attack along the sides of the welds was shown to be associated with the coarse structure of the partially fused zone , and the presence of continuous b-phase on the grain boundaries of the heat-affected zones . this could be avoided by welding at a faster rate with less heat input , e.g by tungsten-arc welding . Oldfield and Twigg investigating the staining of stainless steel tableware , tested blades in contact with galvanised iron and with aluminium in Sheffield tap water at 60 &amp;deg; and 100 &amp;deg; C . they concluded that aluminium containers are reasonably safe for trays or baskets for washing stainless steel cutlery , but galvanised iron can cause staining . aluminium-magnesium-silicon alloy ( similar to h9-p ) pipe , TIG welded , and used for sour gas was inspected by Flournoy after being buried for six years without protection in a soil of sandy loam and broken caliche . where failure had occurred , it was by pitting from the outside , and chlorides were detected in the corrosion product . this experience shows that aluminium is resistant to sour gas , and may be installed bare underground if protection is afforded at local spots of high corrosivity . if one keeps the anti-freeze in the cooling system of one &apos;s car from year to year , one runs the risk of corrosion of the cast-iron parts of the circuit , due to increase in acid content and reduction of inhibitor content of the cooling liquid . this has been shown by Collins and Higgins , who also state that the danger of corrosion of other metals by the deteriorated anti-freeze is slight ; only occasionally has slight pitting been seen with aluminium , and no corrosion necessitating replacement has resulted . investigating the special case of hypereutectic aluminium-silicon alloys under conditions related to car engine cooling systems , Craig and Woods have shown that such alloys , even when coupled to copper , are corroded to a negligible extent if there are suitable inhibitors in the coolant ; in general , hypereutectic aluminium-silicon alloys are more corrosion resistant than cast iron . Sundararajan and Char , continuing their studies of inhibition of the corrosion of aluminium , have assessed the effects of acridine , nicotinic acid , dextrin , thiourea and tannic acid in dilute hydrochloric acid ; all were efficient . in a second paper these authors describe polarisation studies in acid and alkaline solutions , with thiourea and dextrin as inhibitors , and conclude that cathodic protection is possible in acid solutions in the potential range -0.55 to -0.80 V . in both these papers one meets again the curious material previously described by Sundararajan and Char , namely 92 % pure aluminium , containing 3 % Fe , 4 % Mn , 1 % Si ; doubts about decimal points return more strongly than ever . using some impressive mathematics , Bauer and Eddy have compared various possible anode materials for the protection of water tanks . one interesting factor affecting choice is whether or not the water freezes and breaks the anode or suspension ; if it does , aluminium is used , because of its cheapness . chemical conversion coatings have been summarised by Ayres , considering them principally from the point of view of corrosion resistance , which is conferred by low chemical activity and solubility . Wells and Pinner have surveyed recent advances in chemical and electrolytic polishing , on all relevant metals including aluminium . 