4 BULLETIN" 1180, U. S. DEPARTMENT OF AGRICULTURE.- 
soil. It has the disadvantage, however, that it tends to become 
moist under ordinary conditions of storage and handling to a some- 
what greater extent than sodium nitrate. This difficulty has been 
partially overcome by forming the ammonium nitrate into small 
grains and coating them with an oil to lessen the absorption of mois- 
ture. This treatment is comparatively inexpensive. 
Among other methods which have been attempted to overcome 
this handicap of moisture absorption are the production of double 
and mixed salts which are less hygroscopic than ammonium nitrate 
alone, and in the present experiments tests were made with such 
salts as well as with ammonium nitrate. These materials include a 
double salt consisting of ammonium nitrate and ammonium sulphate 
and two mixed salts made by the double decomposition of ammonium 
nitrate with potassium chlorid or with potassium sulphate. The 
products obtained from potassium chlorid and ammonium nitrate 
are ammonium chlorid and potassium nitrate, while with potassium 
sulphate they are ammonium sulphate and potassium nitrate. The 
processes of manufacture of these double and mixed salts are com- 
Earatively simple and inexpensive. However, the necessity of using 
igher grade potash salts than are normally available (particularly 
the chlorid) in order to obtain sufficiently nonhygroscopic mixed 
salts may constitute a rather serious obstacle to their economical pro- 
duction. They have been prepared only on an experimental scale in 
this country. 
Ammonium phosphate will in all probability become an important 
fertilizer salt within the next decade. It is especially desirable 
because of its excellent physical properties and high concentration of 
plant food, containing as it does both nitrogen and phosphorus. It 
has been manufactured in this country to a limited extent as a ferti- 
lizer material, but its commercially successful production is largely 
dependent on the development of a process for cheaply producing 
phosphoric acid. Important advances are now being made in this 
country in the production of phosphoric acid directly from phosphate 
rock by thermal or electrothermal processes. 
Ammoniated superphosphate is obtained by absorbing ammonia 
in acid phosphate, thus providing a carrier for ammonia without the 
use of additional acid. The product is of excellent physical quality 
but has the disadvantage that a part of the phosphate is reverted to 
the citrate insoluble form. It has been produced only on an experi- 
mental scale in the United States. 
Ammonium chlorid has not heretofore been regarded as a fertilizer. 
There is a possibility, however, that it may soon become available 
for such purpose as a product of the ammonia-soda process combined 
with the direct synthetic-ammonia process of nitrogen fixation, and 
hence the value of this material as a fertilizer is of considerable 
interest. 
Urea possesses unusually desirable properties as a fertilizer. It is 
a highly concentrated nitrogen compound, readily available, pos- 
sesses good physical qualities, and when used by the plant leaves no 
undesirable acidic or basic residue in the soil. While at present the 
cost of manufacture for fertilizer use is prohibitive it seems probable 
that this obstacle may soon be overcome. 
Urephos is the product obtained by treating cyanamid with an 
excess of sulphuric acid and neutralizing the latter with ground phos- 
