MANUFACTUEE OF BONE SUPERPHOSPHATE. 179 



It is asserted that crushers working by shock develop more 

 heat than need be. With crushers such as those described work- 

 ing at a great speed, mth the bars of the grating far apart, the 

 temperature does not rise more than with a toothed C3dinder, for 

 the ventilation is very energetic and the friction reduced by the width 

 of the passages.-^ 



Extraction of Fat from Bones. — The extraction of fat from bones 

 is an indispensable operation, even when it is a question of merely 

 converting the bones into dust for the farmer. In fact, bone dust 

 not deprived of its fat is of less value, because the fat decomposes 

 very slowly in the soil, and constitutes an obstacle to the phosphoric 

 acid becoming soluble. 



Fat may be extracted from bones by three processes : (1) By 

 simple boiling in open pans. (2) By the action of steam in closed 

 vessels. (3) By solvents. The extraction of fat by simply boiling 

 leaves the ossein almost intact, but generally there is only obtained 

 a portion of the fat in the bones. 



By extracting the fat by steam, a higher yield of fat is obtained, 

 especially if the operation be continued long enough, but a portion 

 of the ossein is then transformed into gelatine. Now, in manure 

 manufactories this gelatine constitutes a loss and becomes cumber- 

 some because it decomposes rapidly ; if it be diverted into a stream, 

 it infects the rivulets. It is best used in irrigation. Bone dust 

 from bones treated by steam is more soluble than that of bones 

 from which the fat has been extracted by simple boiling ; moreover, 

 it is also more in request by farmers. - 



ing by two machines running tandem as it were, yet here the fine meal made at the 

 outset apparently passes along with the core to the second machine, which it would 

 most certainly block up if fed into it as rapidly as it came from machine No. 1. 

 The crushed bones from No. 1 machine should certainly be screened before 

 passing to No. 2, so that the haunners can get at the lumps without the smaller 

 particles removed by the screen acting as bulfers. There is no getting over the 

 fact that the grinding of bone meal by such machines is costly. It is a pleasant 

 sight to see one go ahead for an hour. It is another to see four or five men idle 

 through blocking up for a quarter to half an hour. — Tr. 



1 The bearings should be kept clean and free from dust as far as practicable ; 

 oily bone dust is liable to set the bearings aflame. The bearings should be 

 covered during grinding and only uncovered for lubrication. Machines revolv- 

 ing at 2000 to 8000 revolutions a minute develop quite enough heat on the 

 bearings without it being increased by fine air-driven bone dust. — Tr. 



2 As far as Great Britain is concerned the translator dissents (see previous 

 note). Moreover, there is no absolute necessity whatever for the manure manu- 

 facturer to turn bone boiler, whatever there may be for the bone boiler to turn 

 manure manufacturer. 



Whether fat extracted or non-fat extracted ground bones decomposes 

 most rapidly in the soil, will depend on circumstances. Many years ago the 

 translator superintended the dispatch of some 30 tons of bone meal made from rag 

 bones, i.e. non-fat extracted. The next year the same customer was supplied with 

 ground bones from bones that had been boiled under pressure. He made a most 



