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Electric units and standards
258
U.S.
]]UREAU OF STANDARDS NOTES.
[J.F.L
more than xo per cent. at 135o ° C. for glass-pot clays ; a softening point corresponding to standard cone No. 30 for crucible and, if possible, higher for glass refractories; a total content of fluxes (iron oxide, lime, magnesia, potash, and soda) of not more than 5 per cent. for crucible and 4 per cent. for glass-pot clays. F r o m the results obtained it was shown that these famous European clays do not differ radically from similar materials found in this country, but that the same results can be obtained with mixtures of known American clays. There is no lack of domestic clays suitable for the uses under consideration, and it is but a question of proper selection. The possibility is pointed out of securing with American raw materials results even superior to those obtained with the foreign clays by mixtures of tw6 distinct types, the open and dense burning clays. The imported clays show certain faults which may be eliminated by the systematic blending of several clays. ELECTRIC UNITS AND STANDARDS.* By J. H. Dellinger.
TI-IE available information on the fundamental electric and magnetic units has hitherto been scattered over an extensive literature. The subject has been condensed and brought up-to-date in this single publication, which gives a unified treatment of the various units, standards, and systems of units. This takes the place of certain previous publications of the Bureau dealing with fragments of the subject. A unit of any physical quantity is defined in general as a definite amount of that physical quantity, specified in some particular way. A standard is the experimental realization or representation of a unit. A system of units is based upon a few selected independent units; i.e., units defined in terms of an arbitrarily chosen standard. There are three independent units in a system of mechanical quantities, and four in an electrical system. The basis of the electric units usually used is the electromagnetic system, in which length, mass, time, and magnetic permeability are taken as fundamental. There are several systems of electromagnetic units in use, differing either in the size of the * Circular No. 6o.
Aug., 1916.]
U. S. BUREAU OF STANDARDS NOTES.
259
fundamental units or in the constants in the defining equations. These are the C.G.S., the so-called" practical," and the Heaviside units. The units used in practice are the " international" units, so called by the international congresses which defined them. They represent the electromagnetic units for practical purposes, and the fundamental international units were so defined as to be equal to the corresponding electromagnetic units as closely as known at the time of definition. The slight differences which have been found by absolute measurements are tabulated in the circular, for the convenience of the occasional investigator who may desire to convert from one system to the other. The system of concrete standards by which the electric units are now maintained is the result of an evolution extending over 70 years. The units are maintained by the national standardizing laboratories in accordance with the decisions of the I9o8 International Conference at London. The circular gives the definitions of the units and detailed information regarding the units and standards of resistance, current, electromotive force, quantity of electricity, capacity, inductance, power and energy, resistivity, and the magnetic quantities. In an appendix, conversion factors for the above units are given, both for units of different systems and for the international units as maintained at different times and places. The laws on electric units in different countries are given. A selected bibliography of the literature pertaining to electric and magnetic units and standards is included. Successful Under-water Coal Storage. J.D. WARDLE. (E~ectric Railway Journcfl, vol. xlvii, No. 26, June 24, I916.)--The Iowa Railway and Light Company, which operates about fifty mi|es of interurban line and has more than 35o miles of high-tension distribution, serving lighting and power consumers in central Iowa, has recently put into service a large under-water coal storage. Iowa coal when piled ignites itself readily, and it is, therefore, necessary to store it in a flooded pit. The coal is reclaimed from the pit with a IS-ton electric locomotive crane. With a consumption of coal of 250 tons a day, it was formerly necessary to carry 5ooo or 60oo tons in reserve in cars at a per diem charge of 45 cents. With underwater storage the number of reserve cars has been reduced to ten and the daily charge from $45 to $4.5o.
U.S.
]]UREAU OF STANDARDS NOTES.
[J.F.L
more than xo per cent. at 135o ° C. for glass-pot clays ; a softening point corresponding to standard cone No. 30 for crucible and, if possible, higher for glass refractories; a total content of fluxes (iron oxide, lime, magnesia, potash, and soda) of not more than 5 per cent. for crucible and 4 per cent. for glass-pot clays. F r o m the results obtained it was shown that these famous European clays do not differ radically from similar materials found in this country, but that the same results can be obtained with mixtures of known American clays. There is no lack of domestic clays suitable for the uses under consideration, and it is but a question of proper selection. The possibility is pointed out of securing with American raw materials results even superior to those obtained with the foreign clays by mixtures of tw6 distinct types, the open and dense burning clays. The imported clays show certain faults which may be eliminated by the systematic blending of several clays. ELECTRIC UNITS AND STANDARDS.* By J. H. Dellinger.
TI-IE available information on the fundamental electric and magnetic units has hitherto been scattered over an extensive literature. The subject has been condensed and brought up-to-date in this single publication, which gives a unified treatment of the various units, standards, and systems of units. This takes the place of certain previous publications of the Bureau dealing with fragments of the subject. A unit of any physical quantity is defined in general as a definite amount of that physical quantity, specified in some particular way. A standard is the experimental realization or representation of a unit. A system of units is based upon a few selected independent units; i.e., units defined in terms of an arbitrarily chosen standard. There are three independent units in a system of mechanical quantities, and four in an electrical system. The basis of the electric units usually used is the electromagnetic system, in which length, mass, time, and magnetic permeability are taken as fundamental. There are several systems of electromagnetic units in use, differing either in the size of the * Circular No. 6o.
Aug., 1916.]
U. S. BUREAU OF STANDARDS NOTES.
259
fundamental units or in the constants in the defining equations. These are the C.G.S., the so-called" practical," and the Heaviside units. The units used in practice are the " international" units, so called by the international congresses which defined them. They represent the electromagnetic units for practical purposes, and the fundamental international units were so defined as to be equal to the corresponding electromagnetic units as closely as known at the time of definition. The slight differences which have been found by absolute measurements are tabulated in the circular, for the convenience of the occasional investigator who may desire to convert from one system to the other. The system of concrete standards by which the electric units are now maintained is the result of an evolution extending over 70 years. The units are maintained by the national standardizing laboratories in accordance with the decisions of the I9o8 International Conference at London. The circular gives the definitions of the units and detailed information regarding the units and standards of resistance, current, electromotive force, quantity of electricity, capacity, inductance, power and energy, resistivity, and the magnetic quantities. In an appendix, conversion factors for the above units are given, both for units of different systems and for the international units as maintained at different times and places. The laws on electric units in different countries are given. A selected bibliography of the literature pertaining to electric and magnetic units and standards is included. Successful Under-water Coal Storage. J.D. WARDLE. (E~ectric Railway Journcfl, vol. xlvii, No. 26, June 24, I916.)--The Iowa Railway and Light Company, which operates about fifty mi|es of interurban line and has more than 35o miles of high-tension distribution, serving lighting and power consumers in central Iowa, has recently put into service a large under-water coal storage. Iowa coal when piled ignites itself readily, and it is, therefore, necessary to store it in a flooded pit. The coal is reclaimed from the pit with a IS-ton electric locomotive crane. With a consumption of coal of 250 tons a day, it was formerly necessary to carry 5ooo or 60oo tons in reserve in cars at a per diem charge of 45 cents. With underwater storage the number of reserve cars has been reduced to ten and the daily charge from $45 to $4.5o.