12 BULLETIN 312, U. S. DEPARTMENT OF AGRICULTURE. 
The processes of Schlutius‘’ and Bretteville,? in which nitric acid 
is employed as a solvent instead of sulphuric acid, are of interest 
because calcium nitrate and soluble calcium phosphate are produced, 
both of which are fertilizer materials. 
Ca,(PO,)>+4HNO,=CaH,(PO,).+2Ca(NO,),- 
Such a mixture is sufficiently high grade to stand the expense of 
long shipment, but the well-known hygroscopic properties of calcium 
nitrate form a drawback to its use in fertilizers and would probably 
necessitate shipping the material in air-tight containers. 
PROCESSES FOR THE PRODUCTION OF PHOSPHORIC ACID OR SOLUBLE 
PHOSPHATES BY COMBINED HEATING AND ACID TREATMENT. 
In general, these processes are not very promising, since they 
involve both acid treatment and the expense of heating the product. 
A list of the patents under this head is given in Table IV, Appendix. 
The process of Scribner * appears to be of much interest. It con- 
sists in either roasting a mixture of phosphate rock and sulphur or 
passing sulphur dioxide over highly heated phosphate rock. In 
either case it is claimed that citrate-soluble phosphate results. 
This scheme is similar to two described under ‘‘Acid treatment.” 
If it accomplishes what is claimed, much unnecessary time and 
expense may be saved in the manufacture of available phosphates. 
From the experience in the Bureau of Soils laboratories, however, it 
would seem rather difficult to conduct this process so as to effect the 
complete conversion of the phosphoric acid into an available form. 
This patent expired in 1900. 
DOUBLE DECOMPOSITION BY MEANS OF AN ALKALI, AN ALKALI SALT, 
OR ALKALINE EARTH. 
All the processes under this head except four depend on heat to 
effect the conversion of insoluble phosphate into a water-soluble or 
citric-soluble form. In Table V, Appendix, a list of the -various 
patents on this subject is given. , 
The object of the processes described below is to obtain a neutral 
or alkaline product containing available phosphoric acid. Owing 
to the acid properties of superphosphate there exists among certain 
farmers considerable prejudice against its use. Fertilizers of the 
type described below have, as a rule, an alkaline reaction, and there- 
fore are popularly believed to counteract any acidity im the soul. 
In the process of Commins, phosphate rock is either heated to 
redness and then saturated with a solution of sodium chloride or 
first treated with the salt solution, heated, and then plunged into 
gas-house liquor. In the more recent process of Lowman,’ a mixture 
1 United States Patent No. 872757 (1907). 4 United States Patents Nos. 74799, 78061 (1868). 
2 United States Patent No. 1011909 (1911). 5 United States Patent, No. 922494 (1909). 
3 United States Patent No. 283426 (1883). 
