4 o AGRICULTURE. [CH. 



phosphate, which gradually enters into the circulation 

 of the plant. The presence of lime in a soil, even in 

 a small proportion, accomplishes this result, and by 

 reason of the less soluble condition to which it is thus 

 reduced, there is also less danger of the phosphate 

 being washed out of the soil. On many light sandy 

 soils the use of ordinary super-phosphate is attended 

 with great loss, as the mono-calcic phosphate is washed 

 out of the soil, by the rain passing through it. In 

 these cases the use of bone is still found the most 

 economical form for adding phosphate of lime to the 

 soil, as this waste is thereby prevented. 



76. It is, however, quite possible for the form of 

 phosphate produced by the action of sulphuric acid on 

 bone or other phosphates to be of the same character 

 as that produced by the decomposition of bones in 

 the soil. By the use of one-half of the sulphuric acid 

 required to make mono-calcic phosphate, we obtain 

 the same form of phosphate of lime as is produced in 

 the soil when bones decompose in the ordinary 

 manner. It is, as we have seen, a more desirable 

 form of phosphate, so far as the healthy growth of 

 vegetation is concerned, and it is by no means im- 

 probable, and much to be desired, that circumstances 

 may shortly lead to its more extensive use. 



77. One other subject, closely associated with 

 super-phosphate, demands notice in passing, viz., the 

 "reduced phosphates. " When a manufacturer 

 has made a large quantity of super-phosphate, and has 

 ascertained its strength by analysis, it very frequently 

 happens that after a lapse of two or three months the 

 super-phosphate is found to be reduced in strength. 

 It is then known as a " reduced super-phos- 

 phate." A super-phosphate having 25 per cent, of 

 soluble phosphate is often found to be reduced to 22 

 or perhaps to 20 per cent. If the value of this super- 

 phosphate were to be determined by analysis, the 

 manufacturer would lose largely, because chemists 





