2l6 MADRAS FISHERIES BULLETIN VOL. Xlll, 



and little water, the pans being usually badly heated by inefficient, 

 badly designed furnaces and flues ; hence the individual fish are 

 kept for a maximum period under heat, in which some are under- 

 heated, some overheated and scorched; after a lengthy heating 

 the fish are gradually forked out from the pan into the press bags 

 and so to the presses ; sometim.es they are evacuated into pits 

 and thence to the presses. Hence the oil is always of a dark 

 colour and greatly contaminated with organic impurities — by 

 quasi-solution — much of which should have remained in the guano. 

 In Tanur the boiling pans are mainly run by steam, the indivi- 

 dual charges are moderate in volume, and plenty of water is used, 

 much of which remains below the false bottom of the pans where 

 the steam pipe lies, so that there is a boiling residuum ready for the 

 next charge : hence rapidity, about 30 minutes, in heating each 

 charge, this period being also utilized in skimming the oil as it 

 rises through the water to the surface : the fluid mass is then let 

 out through the sluice valve into the draining pit or box, whence 

 the drained fluid passes to the receiving pit, while the mass is 

 rapidly removed to the presses and squeezed. Even if steam is 

 not available, improvement may be effected, as at Tanur, by having 

 several boiling pans of moderate size, preferably copper which is 

 a better conductor of heat, using sufficient water and employing 

 drainage pits or boxes, with sufficient presses to press the stuff 

 without delay ; the furnaces should also be carefully designed so 

 as to heat the pans with the maximum of speed and the minimum 

 of fuel. The use of sufficient water in the boiling pans is import- 

 ant since the fish are boiled with much greater rapidity owing to 

 the convection currents set up in the water so that the heat of the 

 fire is transferred rapidly to the water and thence to the fish which 

 are boiled quickly, thoroughly, and evenly ; moreover when there 

 is plenty of water the fish can be easily stirred and there is far 

 less chance of scorching which irremediably discolours the oil 

 skimming is also possible and desirable when there is plenty of 

 water. A false bottom not only minimizes the chance of scorching 

 by interposing a cushion of water between the bottom of the pan 

 and the fish, but this water remains in the pan when the fish are 

 removed, provided the sluice valve is set well above the false 

 bottom. Moreover when in operation, the steam from this water 

 which, owing to the superincumbent weight of fish, rises above 

 212° F., forces its way through the mass and thus tends to heat it 

 rapidly and thoroughly. 



