No. 3 (1921) MANUFACTURE OF FISH OIL AND GUANO 201 



value. This constant is of great importance as it indicates the readiness 

 with which an oil will undergo oxidation, a property on which th^ value of 

 an oil for leather dressing largely depends. 



The principal fish oil used in the leather industry of the United King- 

 dom is cod oil, commercial specimens of which usually have an iodine value 

 of about 155. It will be noticed that the iodine values of these sardine 

 oils from Madras, viz., 154 to 159, approximate very closely to this figure. 



With the exception of the brown oils Nos. 6 and 7, all the samples 

 had low acid values and appeared to have been carefully prepared. The 

 somewhat high acid values of the brown oils would reduce their value for 

 leather dressing, as such oils are usually regarded as unsatisfactory for this 

 purpose. 



Two further samples offish oil were submitted for examination in Feb- 

 ruary 1913 : — 

 No, 10. " Brown oil without stearin." 



These oils were dark brown in colour and had a very unpleasant odour. 

 They were filtered, and then chemically examined with the following 

 results : — 



The constants of these two oils correspond on the whole with those of 

 the previous samples. 



The present specimens have much lower acid value-; than the two 

 samples of brown oil (Nos. 6 and 7) then dealt with, but they were darker 

 in colour and their odour was still more unpleasant. 



The remarks made above as to the uses of the oils are also applicable 

 to the present samples." 



The stearine mentioned in this extract (see also paragraph 39) 

 is the " fish tallow " deposited by the fish oil in considerable 

 quantity, probably amounting to some 25 to 33 per cent of the 

 whole oil. It is not understood why the words " pale brown " are 

 used for samples 4, 5 and 8, since they were yellow when sent and 

 apparently so when seen in 1914 at the Institute. 



