Apparatus for the determination aboard ship of the salinity of sea water by the electrical conductivity method

Ice Patrol Service for the Season 1921."Much of this earlier work was done by A. L. Thuras, a part while he was connected with the National ^Bureau of Standards and a part while he was scientific observer in the Ice Patrol Service.To give satisfactory results the apparatus should be capable of reproducing measurements of the electrical conductivity to 1 part in 4,000, corresponding roughly to changes of 10 mg per liter total salt and something less than 1 part in 100,000 in the density.This could be obtained readily in the laboratory, but the conditions at sea are such as to make the problem much more difficult.For convenience in use, the equipment should be relatively small in size and constitute a unit rather than an assemblage of a number of pieces of apparatus.Further, it should be capable of being operated from the lighting circuit of the ship on which it is installed.The equipment must be sufficiently rugged or so protected as not to suffer mechanical injury during the severest storms, and should be capable of being used during rough weather.The electrical insula- tion must remain good in the presence of an ocean atmosphere, and should not be injured in case sea water is spilled over parts of the apparatus.As the temperature coefficient of the electrical conduc- tivity of sea water is in the neighborhood of 2 or 3 per cent per °C, to obtain a precision of 1 part in 4,000 the temperature must be controlled to better than one-hundredth °C.or provision made to compensate for uncertainties of the temperature.Also the various manipulations necessary in making measurements should be the simplest possible consistent with obtaining the precision sought.