1921.] Wright.—Chemical Technology of Meat Industry. 103 
The tank-water, containing 5J to 7J per cent, of solids, is concentrated 
in the multiple-effect vacuum exaporator until the liquor, now known as 
“ stick,” has a specific gravity of about 1*14 and contains about 40 per 
cent, of solids. This “stick” is syrupy in consistence, and while hot is 
pumped into a mixer equipped with an arrangement for stirring. To the 
“ stick ” is added copperas to an amount which will give 10 per cent, of 
sulphate of iron in the finished, dried, concentrated tankage. 
It should be borne in mind that copperas, which is chemically sulphate 
of iron, contains only approximately 55 per cent, ferrous sulphate, the 
balance being water of crystallization ; consequently in calculating the 
necessary quantity to be added due allowance must be made, otherwise 
certain difficulties will be encountered later. 
The solids of tank-water contain certain very hygroscopic constituents, 
and consequently it is necessary to add an efflorescing material, such as 
copperas, in order to prevent the reabsorption of moisture after drying 
and, indeed, to enable the drying itself to be carried out efficiently. It 
is for this reason that it is important to see that an adequate quantity 
of copperas—or rather, ferrous sulphate—is present in the dried, con¬ 
centrated tankage. 
The “ stick,” containing approximately 40 per cent, of nitrogenous 
solids, with the added copperas, is then dried, usually upon a drying- 
drum type of dryer. The hollow drum is made of metal machined to have 
a perfectly smooth surface. It is heated internally with steam at about 
50 lb. steam-pressure, and dips into a trough containing the “ stick.” 
Kevolving, it carries a film of the material, which is rapidly dried, and is 
removed by knives, which are adjusted as scrapers against the revolving 
roll. 
The dried, concentrated tankage is thus produced in the form of a fine 
powder, which, if properly treated with the requisite amount of iron 
sulphate, retains its quality and does not become sticky or lumpy. 
Instead of drying the “ stick ” upon the drum-dryer it has been found 
possible to mix a certain proportion of the “ stick,” to which has been 
added copperas, with the pressed tankage, drying the whole together in the 
ordinary tankage-dryer. It has also been found practicable to mix the 
“ stick ” and dissolved copperas with the dried tankage, subsequently 
drying the whole in the tankage-dryer. The effect of these methods is to 
increase materially the ammonia content of the tankage, but it has not 
been possible to utilize all the “ stick ” by mixing it with the tankage. 
In plants where the benzine or other solvent extraction treatment is used 
for recovering the fat from the tankage it has been found possible to utilize 
all the “ stick ” by absorption in the dry, fat-free tankage. 
The following is the analysis of a representative sample of concentrated 
tankage : Moisture, 3-35 per cent. ; organic matter, 83-80 per cent. ; ferrous 
sulphate, 9-75 per cent. ; nitrogen, 12-30 per cent. (= ammonia, 14-94 per 
cent.); fat, 0-65 per cent. 
[Dried Blood. (8, 25, 28, 32.) 
Fresh blood contains about 80 per cent, water, the solid matter being 
chiefly nitrogenous in composition and easily coagulated by heat. Various 
methods are in operation to bring about the coagulation of the albuminous 
solids in blood. The material may be run into a tank in which it is boiled 
with open steam until the coagulation is complete, or it may be pumped 
into a tank containing boiling water, the boiling being maintained during 
