32 BULLETIN" 150, IT. S. DEPARTMENT OF AGRICULTURE. 



THE PRODUCTS. 



CHARACTER OF SCRAP. 



The scrap produced from salmon waste is of very high quality. 

 For its value as fertilizer, it is open to criticism only on the score of 

 its high content in oil. This amount of oil probably is not sufficient 

 to prove a serious detriment to the soil nor, possibly, materially to 

 retard the decomposition of the scrap within the soil. But it is dis- 

 advantageous in that it is so much inert material of no fertilizer 

 value. The fact that the oil, of high value if extracted, here plays 

 the role of a worthless diluent of a less valuable product, has no 

 bearing on the value of the scrap as a fertilizer; instead, it con- 

 cerns only the economy of the process by which the material is pre- 

 pared. With regard to the bearing of -the presence of oil in ferti- 

 lizer materials on the value of those materials, attention should be 

 called to the work of Skinner and Beattie, 1 of the Bureau of Soils, 

 having to do with the value of city street sweepings for fertilizer pur- 

 poses. To explain the poor mammal value of this material it was 

 supposed that the presence therein of oil, dropped upon the streets 

 by automobiles, prevented its decomposition, a supposition which be- 

 came a conclusion when it was demonstrated that the same material,, 

 after treatment to remove the oils, showed a greatly enhanced 

 manurial value. This oil is largely, if not entirely, mineral oil, which 

 it is commonly known is much less readily decomposed than animal 

 oils, such as fish oil. In this connection a comparison of the fertilizer 

 values of oily and oilless fish scrap would be of distinct interest. 2 



CHEMICAL COMPOSITION OF SCRAP. 



Samples of salmon scrap representative of the product of the vari- 

 ous manufacturers were received at the laboratory in canvas sample 

 sacks. These samples were ground to a powder that would pass a 

 sieve of 16 apertures per linear inch. Samples of 2 grams each were 

 then dried for about 5 hours in a vacuum drying oven at a tempera- 

 ture ranging between 75° and 85° C. The loss in weight was re- 

 corded as moisture. The same samples were then used for the deter- 

 mination of oil, which was extracted in a Knorr apparatus with 

 ether. Great difficulty was experienced in removing all the moisture 

 without the loss of oil. Nitrogen was determined by Mr. T. C. 

 Trescott, of the Bureau of Chemistry, by the official method. For 

 the determination of phosphoric acid the official gravimetric method 

 was used. In Table VIII are reported the results of analyses of five 

 samples of salmon scrap from an equal number of manufactories. 



1 Circular G6, Bureau of Soils, U. S. Dept. Agr. 



2 Experiments recently made in these laboratories by Skinner and Lindemuth, in which 

 the fertilizing value of oily and oilless fish scrap was compared, showed that the latter 

 (extracted with ether) give pronouncedly better results than the former. 



