12 
BULLETIN 415, U. S. DEPARTMENT OE AGRICULTURE. 
reduced before ignition in order that substantially all of the potash 
niight be subsequently extracted with water. The following experi- 
ment was conducted to test this point: 
A sample of high-grade alunite containing 10.56 per cent total 
potash (K 2 0) was ground to three different degrees of fineness as 
follows: 60 to 100 mesh, 100 to 180 mesh, and 180 mesh and finer. 
Analyses of the separates showed that there was practically no 
segregation of potash in either the coarse or fine material. 
Two-gram samples of each of the separates were weighed out, 
ignited at 750° to 775° C. for 1 hour, extracted with water, and the 
potash determined in the filtrates as before. The results of this 
experiment are given in Table III. 
Table III. — Extraction of potash with hot water from a sample of alunite ground to three 
different degrees of fineness and ignited at from 750° to 775° C. for over 1 hour. 
Sample 
number. 
Degree of 
fineness. 
Total 
K 2 0. 
Amount 
K" 2 ex- 
tracted. 
Proportion 
of total 
K 2 pres- 
ent. 
Amount of 
water re- 
quired for 
extraction. 
12a 
126 
12c 
Mesh. 
60 to 100 
100 to 180 
ISO and 
finer. 
Per cent . 
10. 56 
10. 56 
10.56 
Per cent. 
10.25 
10.45 
10.33 
Per cent . 
97.06 
, 98. 96 
97.86 
160 
160 
227 
The figures given in Table III show pretty conclusively that 
nothing is to be gained by grinding relatively pure alunite finer than 
60 mesh before ignition. In fact it was found that the coarser samples 
decrepitated on ignition to such an extent that three-fourths or 
more of the residue would pass a 180-mesh sieve. 
ECONOMIC CONSIDERATIONS. 
While it was not the purpose of the present investigation to 
enter into details of the cost of separating the several products from 
alunite, it is thought that a short discussion of some of its economic 
features together with a brief consideration of the value of the various 
products and the estimated cost of producing them will prove of 
interest. 
In the extraction of metals from ores or in the manipulation of 
any raw material occurring far from the market for the product 
sought it is usually considered better economic practice to concen- 
trate or carry out the necessary manufacturing processes at a point 
as near as practicable to the source of the raw materials, thus avoiding 
the cost of shipment on valueless gangue or industrial waste. 
In case of the relatively pure alunites of south-central Utah, how- 
ever, it seems to the writer that the advantage lies the other way, 
since practically all of the ingredients of alunite (with the exception 
