174 CHEMICAL FERTILIZERS 



Dissolved Bones, Vitriolized Bones. Bones have been 

 treated with sulphuric acid for many years as a means of 

 obtaining the phosphates in a more soluble form. Some, 

 at least, of the difficulties of solubility have been also over- 

 come in recent years by superior methods of grinding, but 

 when treatment with sulphuric acid was at first commenced 

 dissolved bones had only to compete with raw bones, contain- 

 ing grease and only coarsely ground. There was, therefore, 

 a much greater difference between the dissolved bones and 

 undissolved bones of 50 years ago than there is in those ferti- 

 lizers to-day. The manufacture of dissolved bones is very 

 similar to that of mineral superphosphates. Bones, which 

 should be degreased and finely crushed, are reduced to powder 

 by means of a steel ball mill and passed through a 50-mesh 

 sieve. The bone dust is then mixed with the desired amount 

 of sulphuric acid. Much variation in method takes place in 

 different works, owing to the difficulties of treating bone 

 meal and sulphuric acid. In some works a sulphuric acid 

 rather stronger than that used for superphosphate is employed; 

 such a mixture heats quickly, and reaction takes place at a 

 rapid rate ; there is some slight risk of browning the bones by 

 means of the burning property of sulphuric acid. Owing to 

 the rapidity of the action, the mixing must take place quickly, 

 and the mixture should be transferred to the den without 

 loss of time. Some manufacturers, puzzled by the difficulties 

 of quick mixing and quick charging, prefer to use a much 

 more dilute acid, which, whilst it acts less rapidly, produces 

 a very damp and unsatisfactory dissolved bone. Bones 

 contain far less fluorine and chlorine than do most of the 

 rock phosphates, but some objectionable gases are given off 

 in the manufacture of dissolved bones ; therefore the 

 same precautions are necessary to prevent the workmen 

 being exposed to obnoxious and possibly poisonous fumes. 

 Less carbonic acid is evolved when dissolving bones than 

 when dissolving rock phosphates, hence the mixture does 

 not froth up to a bread-like consistency in the same manner as 

 it does in making superphosphate. Where the manufacturer 

 hasjbeen successful in using a fairly strong'acid with quick 



