With herring offal the extraction process by benzine ensures nothing being removed except the moisture and the oil. None of the liquor with its valuable ammonia is lost. Consequently the whole of the nitrogenous matter is combined with the resultant fertilizing meal.

To indicate the advantage of the benzine extraction process over the old-fashioned method of cooking, pressing, and subsequently drying the pressed cakes the accompanying analyses may prove informative. They refer to herring-mixed meal produced from kippering offal and damaged herring respectively.

Benzine Extraction Process.

Per cent.
Ammonia 11·79
Tribasic phosphate of lime 9·66
Oil 1·10

Old Process.

Per cent.
Ammonia 7·5
Tribasic phosphate of lime 6·5
Oil 15·5

Both essential fertilizing constituents are lower by the second than by the first process. This is not surprising in view of the fact that the subjection of the sludge to pressure drives off the watery liquor which is allowed to escape into the drains, notwithstanding that it carries a pronounced proportion of the ammonia and phosphate. Then it will be seen that the benzine process yields a manure carrying a less proportion of the oil which the farmer regards with misgiving, because the oil has been recovered for sale as such. In other words it will be seen that, under the old process, 14.4 per cent. of oil is allowed to pass to the land where it is not required, instead of to industry where it is in keen request. At the prices which prevailed during the war this represented a wastage of £7—$35—per ton of fertilizer.

Under the extraction or solvent process the meal is turned out in a perfectly dry condition, either for use as a poultry food or fertilizer, the recovery of the oil and drying being completed in the one operation. The method is not only the acme of simplicity but it assures the maximum yield of oil, only 1 per cent. being lost. It is also rapid, it being possible to treat a charge of 8 tons of offal in 10 to 12 hours in one unit.

White fish and general offal do not contain sufficient oil to warrant the expense of solvent extraction. If it should be desired to secure 99 per cent. of the slight proportion the offal carries then submission to the benzine process is imperative, for the simple reason that it cannot possibly be recovered in any other way. The modern system of drying such offal is by steam heat under vacuum or reduced pressure.

This process, to which I have also devoted adequate attention previously, not only enables a product of high quality to be obtained, enabling it to command an enhanced price in the market, but it also conduces towards the retention of the nitrogenous contents of the meal. From the fertilizing point of view this is the main end to be achieved. Colour of the meal is another factor which demands recognition. It plays a far more prominent part in the commercial value of the product than might possibly be conceived. The American drying system, operating along direct fire-heated lines, while efficient so far as it goes, namely, the elimination of the moisture, yields a darker coloured meal, owing to the high temperature which has to be used, while, of course, the nitrogen content is lowered by such practice.