26 HYDROGRAFI. 



this purpose. After the tube had been filled with molasses and the thermometer put in, the piston 

 was forced into the tube by means of a hydraulic press, kindly placed at our disposal by Mr. Nielsen, 

 cand. polvt and director of the Government Laboratory for the examination of cement. The hydrau- 

 lic pressure the thermometer had been subject to, was then calculated by using the magnitude of the 

 force and the diameter of the piston as arguments. Thus all the thermometers were proved 

 at a pressure of 500 atmospheres. 



On the first voyage, a thermometer supplied by the Meteorological Institute was used for the 

 determination of the temperature of the surface waters, but as it appeared that this thermometer 

 only allowed a very inexact determination of the temperature, it was only used at 12 p. m. and 4 a. m., 

 while I measured the other temperatures myself with a thermometer that had the scale etched 

 on the thermometer-tube, and the degrees divided into tenths. On the second voyage, 

 measuring was only performed with a thermometer of the last-named type, which was placed in a 

 case of brass to prevent it from being broken by the frequent use of it 



As the same water of which the temperature was measured was used afterwards for the deter- 

 mination of the specific gravity and the amount of chlorine, provision had to be made to prevent the 

 salinity of the water from being subject to any alteration during the measuring of the temperature. 

 That such a thing might occur, was to be feared in case of the thermometer not being properly wiped 

 off after each single measuring. If for inst the water was allowed to evaporate from the surface of 

 the thermometer, a layer of salt would be deposited on this latter, which, during the use of the same 

 thermometer for the examination of another body of water, would have the effect of altering the sali- 

 nity of this latter. To avoid this inconvenience the thermometer was, when not used, placed in a glass 

 with sea-water, which was frequently renewed, and by the closing of the glass with a cork, the water 

 was prevented from evaporating too quickly. At the beginning canvas buckets were used for the 

 hauling up of the water, but being afraid af salt being lodged in the pores of the canvas of 

 buckets of this kind, and that it might not be properly removed when the buckets were washed out, 

 I had them replaced by metal buckets, in which all deep furrows were filled with melted tin. The 

 water was always hauled up in front of the machine, and after the measuring poured into bottles, 

 which had been properly cleaned beforehand. We had 30 such bottles for temporary conservation of 

 the water, all fitted with properly ground glass-stoppers. In this manner the samples of water were 

 deposited in my laboratory to enable them to adopt the temperature of the room, before the titration 

 and the determination of the specific gravity was to take place. 



DETERMINATION OF THE SPECIFIC GRAVITY. 



The determination of the specific gravity was made with glass-areometers (from Steger in Kiel), 

 of which the expedition had three large sets, but with exception of the few measurings that took 

 place in the North-Sea, all the measurings during both years were made with one and the same areo- 

 meter. At determinations of the specific gravity by Pycnometer, the areometers were 

 adjusted before the departure of the vessel, which also was the case, when the voyages were completed, 



