JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VII DECEMBER 19, 1917 No. 21 



OCEANOGRAPHY. — An instrument for accurate and rapid den- 

 sity measurements on board ship. 1 A. L. Thuras, Bureau of 

 Standards. (Communicated by S. W. Stratton.) 



The ordinary hydrometer has long been discarded for accurate 

 oceanographic work because of the irregularities and variations 

 in its indications. Almost all of these errors are to be found at 

 the surface of the liquid measured, as for instance, changes in 

 surface tension, impurities on the surface influencing the shape 

 of the meniscus on the stem of the hydrometer, and irregularities 

 in the wetting of the stem. These errors are all eliminated in the 

 float, or bobbin, of total immersion. Therefore this method has 

 been investigated and studied with the hope of possibly improving 

 and simplifying it, so that rapid and accurate density measure- 

 ments can be made on board ship. 



The method was probably first suggested by Pisati and de- 

 scribed in 1890 by Reggianni, who used hydrometers of total 

 immersion on board the Washington of the Royal Italian Navy in 

 the Mediterranean in 1883. He used two modifications, one con- 

 sisting of a hydrometer of constant specific gravity and the other 

 consisting of a hydrometer of variable specific gravity. In the 

 first modification, equilibrium in weight of the hydrometer and 

 solution was effected by adding measured quantities of distilled 

 water to the solution; in the second modification equilibrium was 



1 Done under the auspices of the Interdepartmental Committee on Ocean- 

 ography, subcommittee on instruments, apparatus, and measurements. 



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