June 7, 1907] 



SCIENCE 



903 



Experiments show that the rapidity of cor- 

 rosion is directly proportional to the partial 

 pressure of the osygen in the atmosphere 

 above the water containing the iron and there- 

 fore in the water. A reagent which indicates 

 very clearly those portions of the iron at which 

 iron ions are passing into solution, on the one 

 hand, and where hydrogen is passing out of 

 solution with the formation of hydroxyl, on 

 the other hand, was found in ordinary tap- 

 water containing a little phenolphthalein and 

 potassium ferricyanide. The red and blue 

 zones are quickly apparent when any piece of 

 iron is immersed in this solution, and can be 

 rendered more or less permanent if the solu- 

 tionr be thickened with gelatin or agar-agar. 



The potential difEerence which has often 

 been observed between iron and iron oxide, is 

 shown to be occasioned by the unequal con- 

 densation of oxygen upon the two surfaces. 

 For example, magnetic oxide of iron which, 

 under ordinary circumstances in connection 

 with iron, shows a large difference of potential 

 in water or weak electrolj^te, indicates no dif- 

 ference when the system is entirely free from 

 oxygen. 



Differences of potential which can easily be 

 observed upon different portions of an iron 

 plate, may be also explained by the varying 

 capacity of different portions of the iron for 

 occluding or segregating oxygen. 



The electrochemical theory is substantiated 

 by showing that any reagent which increases 

 the concentration of the hydrogen ions will 

 increase the rate of corrosion, while reagents 

 which decrease this, inhibit corrosion. The 

 fact that bichromate and chromic acid inhibit 

 rusting, may be explained by the formation of 

 an enclosing film of oxygen evenly distributed 

 over the surface in a way analogous to that 

 which may be formed by immersion in nitric 

 acid. 



The Analysis of Chlorides and Sulphocyanate 

 Mixtures: M. A. Eosanoff and Abthue E. 

 Hill. 

 To analyze chloride and sulphocyanate 



mixtures is to-day a difficult matter. The 



known gravimetric methods are laborious. 



The known volumetric methods are but little 



more rapid and far from precise. The au- 

 thors have devised a new volumetric method, 

 which is easy of execution and yields results 

 of the highest precision. Its basal facts are 

 as follows : (1) At the temperature of boiling 

 water soluble sulphocyanates are readily oxi- 

 dized by small quantities of nitric acid; (2) 

 most of the hydrocyanic acid produced can be 

 expelled in a short time by boiling; (3) no 

 hydrochloric acid is lost, owing to complete 

 electrolytic dissociation; (4) silver cyanide is 

 somewhat soluble, silver chloride is insoluble, 

 in moderately dilute nitric acid. 



The method can be used to determine chlo- 

 rides in the presence of both sulphocyanates 

 and cyanides, and the authors are endeavoring 

 to extend it to the determination of bromides. 

 Details of the modus operandi will shortly ap- 

 pear in the Journal of the American Chemical 

 Society. 



Gasoline-Soap ' Emulsions ' and their Relation 

 to Sewer Explosions: A A. Breneman. 

 The ' emulsion ' produced by shaking up 

 gasoline or benzine with soap solutions gathers 

 slowly upon the surface of the aqueous liquid 

 forming a thick, creamy paste which is very 

 permanent in closed vessels but disintegrates 

 rapidly on exposure to air by volatilization 

 of the hydrocarbon. The ordinary operation 

 of washing the hands with soap after benzine 

 or gasoline has been used to remove grease, 

 carries off the light liquid as an emulsion. 

 This same emulsion can be made in quantity 

 by shaking up gasoline with a weak soap solu- 

 tion in a stoppered glass cylinder. It then 

 rises in an hour or less to form a thick, white, 

 creamy layer which can be drawn off and 

 kept separately. In this condition it is very 

 permanent, requiring many days to effect an 

 appreciable further separation. Under the 

 microscope it shows a mass of air bubbles 

 studded or coated with minute globules of 

 gasoline. The air within the bubbles is 

 saturated with vapor of gasoline, the soap 

 solution is indifferent to it, and vapor pressure 

 is at an equilibrium throughout the system. 

 The permanence of the mass in a closed 

 vessel is therefore to be expected. In the open 

 air it disintegrates rapidly, giving off gasoline 



