580 U. S. BUREAU OF FISHERIES 



6.16° below zero is reached, enough water in the form of ice has been 

 removed from the brine to leave the liquid portion at a concentration 

 of 22.42 per cent salt. This is the same figure we arrived at when we 

 began with the strong brine. That is to say. at a concentration of 

 22.42 per cent salt and 77.58 per cent water, by weight, and a tempera- 

 ture of 6.16° F. below zero, both ice and salt will separate together or 

 the brine freezes as a mass. This concentration and temperature point 

 is called the cryohydric or eutectic point, shown in Figure 30 where 

 the two curves meet. It is the lowest temperature that can be had 

 with liquid salt brine, whatever the initial concentration may have 

 been. It is useless, therefore, to start with more than 22.42 per cent 

 salt or a specific gravity of brine of 1.171 (about 84.64 per cent 

 saturation at 60° F.) 



Suppose the brine to be of a lower concentration, however, say, 

 20 per cent. The freezing point of such a brine is 0.14° F. above 

 zero. It can be cooled to any temperature above this point without 

 separation of either ice or salt. Ottesen discovered that if brine is 

 less than saturated (that is, less than 22.42 per cent salt) and is 

 cooled until water begins to separate, penetration of salt into the 

 fish immersed in it is at a minimum as long as ice is separating, or 

 as long as the conditions represented are on the lower ice curve in 

 Figure 29. He reasoned thus : If water separates from the brine 

 as ice at this temperature, certainly water can have no tendency to 

 mix with it. A drop of water added to such a brine will not mix 

 with it but will freeze as a pellet of fresh ice or a cluster of ice crystals. 

 Therefore, the water on and in the fish will not combine with the 

 brine or absorb salt, but will freeze without mixing with the brine. 

 If, however, the quantity of warm fish is sufficiently great to warm 

 the brine and thaw out all the separated water ice, penetration will 

 take place. Hence the necessity for having an excess of free ice in 

 the brine when freezing begins. He therefore claims that when the 

 unsaturated brine is at its freezing point 45 and an excess of fresh- 

 water ice is present the surface moisture and skin of the fish freeze 

 immediately and thenceforth form an effective barrier against the 

 further penetration of salt. Table 20 gives the cryoscopic properties 

 of salt brine. 



45 " Freezing point," to fit the use Ottesen makes of it, must be denned as the tem- 

 perature at which water ice begins to separate from a brine of less than 22.42 per cent 

 salt. An important distinction must be made between the use of the term " freezing 

 point " for brine and for water, which has a true freezing point at 32° F. In this sense, 

 only brine of 22.42 per cent salt has a true freezing point — 6.16° F. below zero — at which 

 temperature it will freeze solid without change of temperature. 



