No. 3 (1921) MANUFACTURE OF FISH OIL AND GUANO 21/ 



114. Over an open fire a copper pan is preferable to an iron 

 one because 



(1) Copper conducts better than iron in the proportion of 10 

 to 7 for equal thicknesses of metal ; 



(2) Copper being tough, a pan, if properly supported, may 

 be made much thinner than iron, so that conduction is still more 

 rapid than in the above proportion ; but thin pans must be supported 

 by stays, etc., at various points or the pan would buckle ; 



(3) Iron pans are very apt to rust away rapidly under the 

 influence of salt water, heat, and air, and have to be renewed ; the 

 copper pans at Tanur are 9 or 10 years old ; 



(4) Iron pans, especially if rusty, may discolour the oil ; 



(5) It is difficult to repair a hole worn in an iron boiler espe- 

 cially if, as is usual, the neighbouring parts have worn, whereas a 

 patch can easilv be brazed or riveted in a copper pan ; 



(6) When fairly worn out an iron pan is useless scrap, 

 whereas copper can be sold at its weight value. Hence copper 

 pans are better than iron if the first cost can be afforded. 



It is recommended that steam be used if possible, but in any 

 case that several boiling pans, preferably of copper, of moderate 

 size and with false bottoms, be set over properly designed furnaces ; 

 that sufficient water be used to allow of skimming, or at least to 

 permit of ready stirring, rapid and even heating, and reduction of 

 scorching; that drainage pits be also used to assist in the rapid 

 separation of fluid from solid, and that enough presses be supplied 

 to work off the scrap rapidly. 



115. Rapid separation of the oil from foul water. — The tJiird point, 

 and one of the most important, is the rapid and complete separation 

 of the oil from the dirty water which flows from the drainage boxes 

 and presses into the receiving pits. This requires careful expla- 

 nation — with some repetition — and study, since most of the 

 deterioration of the oil takes place after the presses have done 

 their work ; it is only when the causes of this deterioration are 

 thoroughly understood that good oil will be the rule instead of 

 inferior, and that the purifying and refining processes will be 

 intelligently carried out. 



Fish contain in their tissues large quantities of fluid matter 

 which are largely proteid (nitrogenous) and readily decomposable ; 

 moreover the white fibrous connective tissue is composed of a 

 substance called "collagen" which is albuminoid in character. 



