CH. l] THE EXPLORATION OF THE SEA 13 



The salinity is the total weight in grams of the solid matter 

 dissolved in 1000 grams of water. 



Now sea water is a solution of a great number of different 

 salts of which common salt is the most abundant. But it has 

 been found that the ratio of these different substances to each 

 other is always very nearly the same even if we are dealing with 

 sea water of very variable degrees of saltness. This is so because 

 the sea is Salter or fresher by reason of the removal of pure water 

 from it by evaporation, or by the addition of water to it from the 

 land, not quite pure but practically so because it becomes mixed 

 with such an immense quantity of salt water that the ordinary 

 constituents dissolved in the fresh water are immensely diluted. 

 So it has been possible to draw up tables which enable us to 

 convert one of the values referred to, say salinity, into any other, 

 say density. Only one determination is then required in order to 

 define the character of the water sample, and this is now always 

 the total contents of the water in dissolved halogens. Not only 

 chlorine, but also bromine and iodine are present in solution. 

 The total halogens are then estimated by means of titration by 

 nitrate of silver, a method which is susceptible of a high degree of 

 accuracy, and from this value the other values — specific gravity 

 in situ, and density — are calculated. 



The practical procedure adopted in the International Fishery 

 Investigations is as follows : the sample of water is obtained by 

 means of the Nansen-Pettersson bottle and at the same time the 

 temperature of the water iii situ is taken. The water sample is 

 taken from the bottle and stored in a clean glass tube or bottle 

 and sealed. These samples are then sent ashore to be worked up. 

 Standard solutions of silver nitrate having previously been pre- 

 pared the titration is carried out. This is done in a special burette 

 consisting of a wide glass bulb containing the greater part of the 

 silver solution required for the titration. The narrow stem of the 

 burette is graduated so that the estimation of very small quanti- 

 ties of the solution delivered is easy. The burette gives direct 

 readings — that is, it indicates the amount of total halogen repre- 

 sented as chlorine in the water sample examined in parts per 

 1000. Standard sea water is prepared by the Central Laboratory at 

 Christiania and is supplied to the workers in the various countries. 



