spy Digitized by the Internet Archive in 2011 with funding from The Library of Congress http://www.archive.org/details/onreductionofhydOOtitt | G C 15S I.T62 pOpy J UNITED STATES COAST AND GEODETIC SUEVEY T. C. MENDENHALL SUPERINTENDENT WEIGHTS AND MEASURES ON THE REDUCTION HYDROMETER OBSERVATIONS OF SALT WATER DENSITIES Submitted for publication Feb. 18, 1890 By O. H. TTTTMANUNT, Assistant, In oharge of the Office of Standard "Weights and Measures Revised for republication Feb. 1, 1892 APPENDIX NO. 6-REPORT FOR 1891 WASHINGTON GOVERNMENT PRINTING OFFICE 1892 UNITED STATES COAST AND GEODETIC SUEVEY T. C. MENDENHALL SUPEKINTENDKNT WEIGHTS AND MEASURES ONTHK REDUCTION OF HYDROMETER OBSERVATIONS OF SALT WATER, DENSITIES Submitted for publication Feb. 18, i8go By O. H. TITTMANN, Assistant, In charge of tlie Office of Standard Weights and Measures Revised for republication Feb. i, 1892 APPENDIX No. 6-REPORT FOR 1891 WASHINGTON GOVERNMENT PRINTING OFFICE 18 92 a V 3r rEB 13 1905 APPENDIX NO. 6—1891. ON THE SEDUCTION OF HYDEOMETEE OBSEEVATIONS OF SALT-WATEE DENSITIES. Submitted for publication, February 18, 1890, by O. H. Tittmann, Assistant, in charge of tbe Office of Standard Weights and Measures. Eevised for republication, February 1, 1892. The hydrometers heretofore in use in the Coast and Geodetic Survey for determining the density of ocean water are described in Appendix 16, Coast Survey Eeport for 1874. They are of glass, of the usual form, and are decimally divided on the stem. Each hydrometer is ac- companied by a copper vessel for holding the water, to which a ther- mometer is attached with the apparatus described in that appendix. Fahrenheit thermometers were used, and the densities given by the graduation of the hydrometer were referred to pure water at 60° F. The introduction of the centigrade scale and of a graduation to give densities referred to pure water at 4° C. necessitates the publication of a convenient table for reducing the observations to the temperature of 15° C, recently adopted by this Survey and by the U. S. Fish Commis sion. The hydrometers hereafter issued will be standardized at this temperature. The following table for the reduction of observed densities to 15° C. is taken from Dittmar, Physics and Chemistry, Challenger Expedition, Vol. 1, after applying to his densities one-half of the correction given by him for reducing them to Thorpe and Bucker's results. The tem- perature at which the density of the standard water is 1*02600 has been shifted from 15 0, 56 to 15° C. for the sake of getting an integer number. The table has been rearranged so as to give the densities of the stand- ard water multiplied by 1000 for whole degrees and tenths from 0° to 30 o, 9 C. on one page. The ratio designated q> (t) by Dittmar is omitted, and only its recip- rocal is given in the column headed m. The values there given apper- tain to the temperatures on the same horizontal lines given in the first 275 276 U. S. COAST AND GEODETIC SURVEY. column. The use of 'this function is illustrated in the examples in which it appears as a multiplier for the purpose of allowing for the different rates of expansion between standard water and the water the density of which is being determined. The last column has been added to this table for convenience, and gives the correction for change in the volume of the hydrometer itself. The values given have been computed for the mean reading 1026, and with the assumed coefficient of cubical expansion for glass a = •000025. The use of the table will appear from the following examples : Example. I. II. o 23-0 . — 01 10-5 — -2 Obs. temp. Corr. to thermometer. Corrected temp. = t. Observed hydr. reading. Corr. for expansion of hydr. — a. Corr. for hydrometer constant. Observed density at ^=OD. Density of standard water at /= SD. OD -SD. m, tabular multiplier. m(OD — SD.) Standard water at 15 C. Corrected density at 15 . 229 102 1 -oo — 0-20 IO3 1029-29 +: -i2 I020-8o 1023-99 1029-41 1026-92 — 3-19 IOl8 4-2-49 •987 — 3-25 I026-00 4-2-46 1026-00 IO2275 1028-46 For observations which have been reduced to 60° F., made with the old hydrometers indicating densities referred to pure water at 60° F., it will suffice to subtract the constant 0-82 from the result in order to convert the latter into absolute densities at 15° O. Example : Given 1024-00 the density of salt water at 60° F. referred to pure water at 60° F., 1024-00 - 0-82 = 1023-18 its density at 15° C. 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