596 U. S. BUREAU OF FISHERIES 



The writer found by experiment (a) that the ratio of thickness 

 of foam layer to depth of liquid brine obtainable with any particular 

 brine is constant — that is, no amount of agitation of any particular 

 specimen of brine will make a foam thicker than a definite maxi- 

 mum — and this ratio usually does not exceed 1 to 1; (b) that increas- 

 ing contamination increases the ratio of foam thickness to brine 

 depth ; and (<?) the constituents that cause foam remain in the foam. 

 If the maximum foam is produced in a brine by agitation, and if 

 the liquid brine is drawn off from the foam and this process is re- 

 peated two or three times, the foam-producing constituents are 

 removed and the brine does not foam until it is again contaminated. 

 These facts point out a way to overcome difficulties from foam in 

 brine freezers. The surface materials — blood and slime — that cause 

 foam should be washed off. The brine vessel should be at least twice 

 as deep as would be necessary for the liquid brine alone to allow for 

 the gathering foam, and provision should be made for this foam to be 

 carried away, draining free of the brine meanwhile. The contami- 

 nating impurities are thus automatically and continuously removed 

 from the brine. In the case of the spray freezer this foam overflows 

 into the washing compartments at each end. 



RUSTING OF METAL PARTS 



This highly complicated subject has received much study by chem- 

 ists, electrochemists, and engineers and can not be discussed at length 

 here. 65 Briefly, the brine should, if possible, be kept slightly alkaline 

 with lime or a small amount of caustic soda. This may not be prac- 

 ticable in the spray freezer because of the intimate contact of the brine 

 spray with air and consequent rapid absorption of carbon dioxide. 

 Neither is this treatment effective in tanks where fish are in contact 

 with brine, because these alkalis react and combine with the fish flesh 

 and with the slime and fats coming from the fish. The composition 

 of the metals of which the apparatus is composed has much to do 

 with corrosion, and there are several resistant alloys on the market 

 that eventually may be used for making freezing apparatus. Among 

 these alloys are Monel metal, duriron. and an aluminum silicon alloy. 



RAPID FREEZING IN CELLS OR MOLDS 



In the foregoing methods of freezing, the fish are in immediate 

 contact with the brine during the freezing process. Immediate con- 

 tact secures the advantage of the greatest possible effective surface 

 and the best possible rate of transfer of heat for a given difference 

 in temperature. On the other hand, as has been seen in the discus- 

 sion, the composition of the brine is limited practically to a solution 

 of salt in water, with which the lowest possible temperature attain- 

 able is 6.16° F. below zero, though by addition of small amounts of 

 other substances this temperature might be lowered a few degrees. 

 Also, difficulties arising from the penetration of salt into and inter- 

 action with the tissues of the fish have necessitated serious considera- 



05 For a full discussion of corrosion see " Symposium on corrosion," papers by 19 

 authors, Industrial and Engineering Chemistry, vol. 17. April. 1925. pp. 335-392, Ea'ston. 

 See also " The corrosion of metals by refrigeration brines," by E. P. Poste and Max 

 Donauer 1 . The Milk Dealer, February. 1923 : " The chemistry of the brine tank." by B. S. 

 Hull. Ice Cream and Refrigeration, March. 1923 ; " The chemical treatment of refrigera- 

 tion brines to prevent corrosion," by E. P. Poste. The Dairy World, December, 1924, 

 pp. 41-46. 



