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Electrolytic corrosion of iron in soils
July, I913.] NOTES FROM U. S. BUREAU OF STANDARDS.
97
sphericaLseed called rape seed proved to be much better than the commonly used flaxseed, while for larger measures dried peas zre recommended. The effects of varying heights of fall of the seed, of shaking down or jarring the seed during the test, and of different methods of striking off the surplus seed are discussed. Results varying from one part in IOO to one in 400 may be obtained by this method. Finally the various gauges on the market for determining the accuracy of measures, po.rticularly dry measures, by measurements of their dimensions are described, and simple formulm are given for the rapid computatio n of the volume of measures by the linear dimensions. Results by this method vary i,n accuracy from 2 per cent. to 0. 5 per cent. ELECTROLYTIC CORROSION O1~' IRON IN SOILS.* By Burton McCollum and K. H. Logan.
TI-IIS is an experimental paper dealing with the fundamental laws governing electrolytic corrosion of iron imbedded in soils. The results are expressed in terms of electrolytic corrosion efficiency. If the corrosion of the anode is the sole reaction involved at the anode, then according to F a r a d a y s law 96,54 ° coulombs are required to corrode one gramme-equivalent of the metal, and the corrosion efficiency is said to be ioo per cent. In most cases, however, the actual corrosion noted is either greater or less than this amount, and the percentage which the actual corrosion in any case is of the theoretical amount is called the efficiency of electrolytic corrosion. The experimental data presented in the paper show how the efficiency of corrosion is affected by the varying physical conditions encotmtered in practice. It is found that current density has a marked effect on the efficiency corrosion of iron in soils, the efficiency being in general greater the lower the current density. In saturated soils efficiency of corrosion may vary between 20 per cent., and about 14o per cent., for the range of current densities between 5 milliamperes and .o 5 milliampere per square centimetre. Moisture content in the soil also has a marked effect on efficiency of corrosion, the corrosion being in general greater with increasing moisture content up to saturation of the soil. *Technologic Paper No. 25, Bureau of Standards.
98
NOTES FROM U. S. BUREAU OF STANDARDS.
Temperature changes within the limits commonly ,met with in practice, the amounts of oxygen present in the soil, and the depth of burial of pipes below the surface have no material effect on corrosion efficiency. The voltage impressed on the electrodes likewise has no material effect on the corrosion efficiency except in so far as the current density may be affected. The pitting of iron imbedded in soils is found to be affected not only by a non-homogenous condition of the iron itself, but also by the chemicals contained in the soils; certain chemicals, such as nitrate, for example, give rise to comparatively uniform corrosion, whereas certain others, particularly chlorides, produce much greater pitting ,effects. While it is found that the amount of oxygen present has no appreciable effect on the corrosion efficiency, it does affect in a marked degree the character of the end products formed. If the corrosion is rapid and the supply of oxygen small there will be a preponderance of magnetic oxide, "while if the rate o~ corrosion is slow and the supply of oxygen abundant, the ferric oxide ~vill predominate. Owing to the fact that the supply of oxygen around the pipes buried in earth is always more or less limited the character of the oxides formed gives some indication as to the rate of corrosion, and thus indirectly the cause of the corrosion if local conditions are properly considered. There is no material difference in the efficiency of corrosion shown by the various kin'ds of iron commonly used in the manufacture of underground pipes so long as physical conditions are similar. In actual practice, however, wide variations of corrosion in all kinds of iron may be expected, and the results bf a large number of tests show that under most practical conditions the corrosion efficiencies will range between 5o and IIo per cent. T h e paper also gives a great deal of data on the subject of the resistance of soils and its variation with temperature, moisture content, and other physical conditions, and ,discusses the relation between these resistar~ce changes and stray current electrolysis. T H E Bureau of Standards will shortly issue the Technologic Paper No. 14 on "Legal Specifications for Illuminating Gas," which is-a brief discussion of the recommendations made by tl~,is Bureau for State or city laws to control lhe quality of illuminating gas sold.
July, I913 .] NOTES FROM U. S. BUREAU OF STANDARDS.
99
The Bureau untLertook several years ago an investigation of calorimetric standards and of flame standards for gas photometry, but as the work progressed it became evident that other phases of gas testing were equally deserving of attention, and the field of the investigation was therefore extended to include all gas-testing work. As the heating value of a gas is a better measure of its usefulness for power, heating, or lighting with mantles than is the candle-power of the gas, the heat delivered to customers should be measured and controlled in order to insure good service. For open-flame lights only, the candle-power must be maintaJned. As many persons still use such burners, even though they are less economical than a mantle, the candle-power can not be entirely overlooked. The Bureau of Standards proposes that a secondary requirement be fixed by cities to insure sufficient candle-power of the gas for this use, and that the heating value be made the principal basis of gas rating. The basis of rating of the gas and its purity are also discussed in this paper. Copies may be had by addressing the Bureau of Standards, Department of Commerce, Washingtoti, D. C., referring to Technologic Paper No. I4.
T H E F U N C T I O N OF TIME IN T H E V I T R I F I C A T I O N OF CLAY.
,THF. Bureau of Standards is sending to press Technologic ....Paper No. 17 upon the function of time in the vitrification of ,day. The paper is a study of six clays which were heated to ~tbeir maturing temperatures at definite rates and comparing the iheat effect by means of porosity and shrinkage determination. ~- Time is an exceedingly important factor in the maturing of d a y s and bodies. A certain result may be obtained either b y i the use of a higher temperature for a shorter time or a lower temperature for a longer time. This f~ct we see constantly illustrated in the firing of all kinds of clay products, the melting of glass, the softening of pyrometric cones, etc. Yet there are ,definite thermal limits to which such relations are confined, These correspond to the Icfwest temperature at which partial softening, which is a necessary condition of vitrification, can take place.
97
sphericaLseed called rape seed proved to be much better than the commonly used flaxseed, while for larger measures dried peas zre recommended. The effects of varying heights of fall of the seed, of shaking down or jarring the seed during the test, and of different methods of striking off the surplus seed are discussed. Results varying from one part in IOO to one in 400 may be obtained by this method. Finally the various gauges on the market for determining the accuracy of measures, po.rticularly dry measures, by measurements of their dimensions are described, and simple formulm are given for the rapid computatio n of the volume of measures by the linear dimensions. Results by this method vary i,n accuracy from 2 per cent. to 0. 5 per cent. ELECTROLYTIC CORROSION O1~' IRON IN SOILS.* By Burton McCollum and K. H. Logan.
TI-IIS is an experimental paper dealing with the fundamental laws governing electrolytic corrosion of iron imbedded in soils. The results are expressed in terms of electrolytic corrosion efficiency. If the corrosion of the anode is the sole reaction involved at the anode, then according to F a r a d a y s law 96,54 ° coulombs are required to corrode one gramme-equivalent of the metal, and the corrosion efficiency is said to be ioo per cent. In most cases, however, the actual corrosion noted is either greater or less than this amount, and the percentage which the actual corrosion in any case is of the theoretical amount is called the efficiency of electrolytic corrosion. The experimental data presented in the paper show how the efficiency of corrosion is affected by the varying physical conditions encotmtered in practice. It is found that current density has a marked effect on the efficiency corrosion of iron in soils, the efficiency being in general greater the lower the current density. In saturated soils efficiency of corrosion may vary between 20 per cent., and about 14o per cent., for the range of current densities between 5 milliamperes and .o 5 milliampere per square centimetre. Moisture content in the soil also has a marked effect on efficiency of corrosion, the corrosion being in general greater with increasing moisture content up to saturation of the soil. *Technologic Paper No. 25, Bureau of Standards.
98
NOTES FROM U. S. BUREAU OF STANDARDS.
Temperature changes within the limits commonly ,met with in practice, the amounts of oxygen present in the soil, and the depth of burial of pipes below the surface have no material effect on corrosion efficiency. The voltage impressed on the electrodes likewise has no material effect on the corrosion efficiency except in so far as the current density may be affected. The pitting of iron imbedded in soils is found to be affected not only by a non-homogenous condition of the iron itself, but also by the chemicals contained in the soils; certain chemicals, such as nitrate, for example, give rise to comparatively uniform corrosion, whereas certain others, particularly chlorides, produce much greater pitting ,effects. While it is found that the amount of oxygen present has no appreciable effect on the corrosion efficiency, it does affect in a marked degree the character of the end products formed. If the corrosion is rapid and the supply of oxygen small there will be a preponderance of magnetic oxide, "while if the rate o~ corrosion is slow and the supply of oxygen abundant, the ferric oxide ~vill predominate. Owing to the fact that the supply of oxygen around the pipes buried in earth is always more or less limited the character of the oxides formed gives some indication as to the rate of corrosion, and thus indirectly the cause of the corrosion if local conditions are properly considered. There is no material difference in the efficiency of corrosion shown by the various kin'ds of iron commonly used in the manufacture of underground pipes so long as physical conditions are similar. In actual practice, however, wide variations of corrosion in all kinds of iron may be expected, and the results bf a large number of tests show that under most practical conditions the corrosion efficiencies will range between 5o and IIo per cent. T h e paper also gives a great deal of data on the subject of the resistance of soils and its variation with temperature, moisture content, and other physical conditions, and ,discusses the relation between these resistar~ce changes and stray current electrolysis. T H E Bureau of Standards will shortly issue the Technologic Paper No. 14 on "Legal Specifications for Illuminating Gas," which is-a brief discussion of the recommendations made by tl~,is Bureau for State or city laws to control lhe quality of illuminating gas sold.
July, I913 .] NOTES FROM U. S. BUREAU OF STANDARDS.
99
The Bureau untLertook several years ago an investigation of calorimetric standards and of flame standards for gas photometry, but as the work progressed it became evident that other phases of gas testing were equally deserving of attention, and the field of the investigation was therefore extended to include all gas-testing work. As the heating value of a gas is a better measure of its usefulness for power, heating, or lighting with mantles than is the candle-power of the gas, the heat delivered to customers should be measured and controlled in order to insure good service. For open-flame lights only, the candle-power must be maintaJned. As many persons still use such burners, even though they are less economical than a mantle, the candle-power can not be entirely overlooked. The Bureau of Standards proposes that a secondary requirement be fixed by cities to insure sufficient candle-power of the gas for this use, and that the heating value be made the principal basis of gas rating. The basis of rating of the gas and its purity are also discussed in this paper. Copies may be had by addressing the Bureau of Standards, Department of Commerce, Washingtoti, D. C., referring to Technologic Paper No. I4.
T H E F U N C T I O N OF TIME IN T H E V I T R I F I C A T I O N OF CLAY.
,THF. Bureau of Standards is sending to press Technologic ....Paper No. 17 upon the function of time in the vitrification of ,day. The paper is a study of six clays which were heated to ~tbeir maturing temperatures at definite rates and comparing the iheat effect by means of porosity and shrinkage determination. ~- Time is an exceedingly important factor in the maturing of d a y s and bodies. A certain result may be obtained either b y i the use of a higher temperature for a shorter time or a lower temperature for a longer time. This f~ct we see constantly illustrated in the firing of all kinds of clay products, the melting of glass, the softening of pyrometric cones, etc. Yet there are ,definite thermal limits to which such relations are confined, These correspond to the Icfwest temperature at which partial softening, which is a necessary condition of vitrification, can take place.