2l8 MADRAS FISHERIES BULLETIN VOL. XIII, 



These cells and tissues are softened and ruptured by heat and 

 pressure so that their contents pass out with the fluids as they 

 exude from the draining boxes and presses. Moreover these proteid 

 matters are largely soluble in water; also in oil, though the solu- 

 tion in such case may be only a pseudo-solution or colloidal 

 suspension (Southcombe). Hence when even fresh fish is boiled 

 and pressed, especially when the boiling is long and the press 

 bags coarse, a quantity of " impurities," that is non-fatty matters, 

 pass out in the mixed oil and water; these may be solid, viz., 

 fragments of tissue, bone, scales, etc., whether coarse or fine ; 

 they may be large and heavy enough to fall at once to the 

 bottom of the fluid or be retained by a strainer, or they may 

 be so minute as to remain in suspension for a considerable 

 period ; or they may be dissolved so that even filtration is useless, 

 or suspended as minute particles of water, or colloidal suspensions 

 such as particles of albumen. The soluble and suspended matters 

 are derived from the cells of the tissues, ruptured by heat or 

 pressure, and contain some of the proteid constituents of the fish, 

 all of which are readily decomposable and some perhaps already 

 on that way. 



When the fish is not fresh but tainted or even slightly decom- 

 posed, the action of bacteria, enzymes, etc., on the tissues, 

 especially on the nitrogenous proteid matter, is very marked ; 

 malodorous and even poisonous decomposition products are 

 abundantly formed which are soluble and are consequently dis- 

 solved in the water and are also taken up by the oil whether 

 directly as colloidal suspensions or indirectly in the suspended 

 water; in any case the contact of these products with the oil not 

 only imparts a nauseous taste, odour, and bad colour to the oil but 

 hydrolyses (decomposes) the oil itself so that free fatty acids are 

 formed with the result of acidity and rancidity. The longer there- 

 fore that the foul water with its putrifying and hydrolysing 

 contents remains in contact with the oil, the more such oil deterio- 

 rates, the worse it smells and appears, and the more difficult it is 

 to purify and refine. Hence it is essential — 



(1) to separate the foul water from the oil as quickly as 

 possible ; 



(2) to eliminate, partly or wholly, from the oil the impurities 

 held by the oil itself. The usual method is at best partial elimi- 

 nation ; complete depuration means refinement which will be 

 separately considered. 



