6 BULLETIN 1280, U. S. DEPARTMENT OF A.GEICULTURE 
The percentages of nitrogen, phosphoric acid, and potash in almost 
all these raw materials are comparatively low. Xo nitrogen deposit 
or waste material contains more than 15 per cent of nitrogen. The 
Alsatian potash deposits may run as high as 20 per cent of potash, 
but there are no known deposits or materials in this country which 
contain more than 12 per cent of potash. Phosphoric acid occurs in 
fairly high concentration in phosphate rock, but in the process of 
manufacturing commercial acid phosphate the concentration is 
reduced to about 16 per cent. 
Other materials, such as garbage tankage, may contain as little as 
3 per cent of available plant food. When the products from these 
various sources are compounded into mixed fertilizer, the concentra- 
tion of the mixture must always be less than that of the most con- 
centrated material used in its preparation. Complete fertilizers 
containing as low as 10 per cent of total plant food constituents hare 
been made, and for many years the average composition of the com- 
mercial mixed fertilizers could be represented by the analysis formula 
2-8-2, i. e., 2 per cent NH 3 , 8 per cent P 2 5 , and 2 per cent K 2 0, by 
weight in the mixture. 
If low-grade materials could be obtained in unlimited' quantity 
near all points of consumption, there would perhaps be little economy 
in increasing their concentration. It is recognized that in the use of 
such materials there may be advantages which are lacking in the use 
of more concentrated materials: (1) A' market is afforded for indus- 
trial by-products which would not have a market otherwise; (2) the 
fertilizing constituents in these materials may vary greatly in avail- 
ability and thus serve to supply food to the plant throughout the 
growing season; (3) while many constituents of low-grade materials, 
such as sulphur and different forms of organic matter, add nothing 
to the commercial value of a fertilizer, they may nevertheless have a 
beneficial effect on many soils; (4) many low-grade materials have 
properties which improve the physical condition of the whole mix- 
ture ; and (5) , small amounts of plant food per acre can be applied more 
conveniently in the form of low-grade than very high-grade materials. 
It happens, however, that the use of fertilizers is now increasing most 
rapidly in those States that have a limited supply of many fertilizer 
materials, and the cost of handling and transporting low-grade ferti- 
lizers is a very serious disadvantage to their use in such localities. 
This disadvantage has long been recognized, and considerable 
advance has already been made in increasing t\\c concentration of 
many materials which require shipment to a distance. Commercial 
Chilean caliche, containing as low as 15 per cent sodium nitrate, is 
refined before shipment to a product analyzing 90 to 95 per cent 
-odium nit rale. Some of the German potash salts shipped to this 
country have been concentrated from about 9 per cent to 60 per 
cent potash, while a large proportion of the western potash salts 
produced since the war have been refined from a relatively low-grade 
material to one containing as high as (V2 per cent potash. By the 
proper selection of these and other materials, the average analysis of 
mixed fertilizers has undergone a gradual increase in the last 10 
years, amounting to about 30 per cent. 
It i^ generally admitted, however, that fertilizers of still higher 
concentration are desirable, and there i>< now an active campaign to 
raise the analyses of mixed fertilizers, and to limit 'the number of 
analysis formulae. Action along these lines was taken at five con- 
