102 The N.Z. Journal of Science and Technology. [June 
process the extraction takes place continuously with a limited amount of 
solvent charged once for all into the apparatus, which is merely an 
enlarged form of the well-known soxhlet extractor employed in the 
laboratory. Very little solvent is necessary to effect extraction, the same 
solvent being used over and over again. 
The ammonia and phosphate contents of the treated tankage are 
increased in proportion to the amount of fat extracted, none of the 
ammonia and phosphate being lost in the process. 
The principal obstacles lie in the insurance restrictions, and the low 
grade of fat recovered. 
The following results of the analysis of tankage have been obtained :— 
Table VI. 
High Grade. 
Low Grade. 
Degreased. 
Per Cent. 
Per Cent. 
Per Cent. 
Moisture 
5*82 
6*00 
3*20 
Organic matter 
.. 68*73 
65*05 
70*30 
Tricalcic phosphate 
.. 21*85 
25*62 
23*55 
Nitrogen 
8*00 
6*30 
10*70 
(=Ammonia) . . 
.. (=9*73) 
(=7*66) 
(=13*01) 
Fat 
12*50 
17*00 
2*00 
As a stock-food : Protein, 50-0 per cent. ; fat, 12*50 per cent. 
Concentrated Tankage. (8, SO.) 
The aqueous glue-like liquor which is produced during the rendering of 
animal-tissues under steam-pressure is chiefly the condensed steam in 
which is dissolved certain of the nitrogenous constituents of the meat-and- 
bone material; this liquor is technically known as “ soup,” and contains 
usually from to 7J per cent, of solids, but may contain as much as 
10 per cent. The solids in solution are principally the gelatinous materials 
of the bones and of the stomachs, together w T ith the water-soluble extractives 
of the flesh ; these are essentially nitrogenous in character. 
The recovery of the solid matter from this tank-water, or “soup,” marks 
an important step forward from a sanitary as well as an economic point of 
view. Hitherto the thousands of gallons which were daily produced at each 
rendering-plant had been run to waste down the sewer, constituting a 
problem in sewage-disposal, as well as a waste of valuable material. The 
installation of multiple-effect vacuum evaporators stimulated the recovery 
of the solid matter from dilute liquors, and the application of this method 
in dealing with tank-water has proved successful, and in consequence a 
valuable by-product is now manufactured, containing from 12 to 13 per 
cent, of nitrogen. 
The tank-water, after any fat upon it has been skimmed off, should 
be kept very hot until it is put through the evaporator. The reason for 
this lies in the fact that it is a readily putrescible substance, and provides 
an excellent medium for the growth and development of bacteria, which 
decompose it into ill-smelling compounds, which not only make it difficult 
to handle properly, but render the process one which is specially liable to 
become a nuisance. If, however, the tank-water is not allowed to fall 
below 160-170° F. in temperature bacterial growth is checked, and the 
material can be held free from decomposition and liability to become a. 
nuisance. 
