104 The N.Z. Journal of Science and Technology. [June 
the process of admitting the blood. The addition of ferric sulphate to 
the boiling water is advantageous. After the blood has been thoroughly 
coagulated, or clotted, it is then pressed, or centrifugalized, as the case may 
be, in the same manner as the wet tankage. After this process it contains 
about 50 per cent, of water. The pressed blood is then dried in a dryer 
similar to that used for tankage ; it may be handled separately, or it may 
be mixed with the tankage, thus enhancing the nitrogen content of the 
dried tankage. 
If the blood is dried separately and held as dried blood it may be 
possible to utilize it, in part at least, as a stock-food. There is some doubt 
as to whether the chemist or the pig first discovered that dried blood was 
of value as a food for pigs, but recent research upon the subject of feeding- 
stuffs for stock has shown that when dried blood is added to the diet a 
decided increase in weight was found above that of pigs fed without blood 
but on a similar diet otherwise. Recent experiments in Britain and in 
America have shown that tankage if properly handled, and especially if 
•dried under vacuum, as well as dried blood, can be profitably utilized 
for feeding poultry and pigs. Ordinarily, dried blood is used as a 
fertilizer. 
A note of caution must be sounded here. It must not be assumed 
that any material which for the purposes of fertilizer-uses can be classed 
as either tankage or blood may be used as a feeding-stuff for stock. Only 
material which has been manufactured from fresh and undecomposed meat, 
bone, or blood should be used for this purpose. Otherwise it is merely 
courting litigation to supply for live-stock a foodstuff which may, in 
consequence of putrefaction at some stage of its preparation, have developed 
substances toxic to animals. 
An average sample of dried blood shows an analysis : Moisture, 5*50 
per cent. ; organic matter, 88-75 per cent. ; nitrogen, 13-60 per cent. 
(= ammonia, 16-53 per cent.). As a stock-food : Protein, 85-00 per cent. 
Bonedust. (21, 28, 32.) 
The practice in regard to the treatment of bones varies greatly, but in 
this country the principal utilization is in connection with fertilizers. It 
is not without interest, however, to consider what is done in other countries 
with bones. From bones may be obtained by appropriate treatment bone- 
charcoal ; oils ; pigment for paints and shoe-blacking; sulphate of ammonia ; 
cupels ; and vitrified bone for use in making opal glass and in the manu¬ 
facture of knife-handles, combs, fans, and buttons. Bones furnish also 
glue, gelatine, and bonedust, and can be used as a starting-point in the 
manufacture of phosphorus. 
In connection with the frozen-meat industry of this country the principal 
process of manufacture through which the bones of the slaughtered stock 
are passed is in connection with the ultimate utilization of this product 
for fertilizer purposes. Incidentally, of course, a certain amount of tallow, 
oil, and concentrated tankage is obtained. 
If not mixed with the general output of offal sent to the rendering- 
plant, and thus ultimately converted into tankage, the bones are placed 
in the digesters and cooked for several hours under steam-pressure. The 
tallow is recovered, and the gluey liquor, or “ soup,” contains usually, but 
not invariably, a high enough percentage of nitrogenous matter to warrant 
the cost of evaporation for concentrated tankage ; but this is a question 
which is determined by actual test at the time. 
