12 



BULLETIN 415, U. S, DEPAETMENT OF AGEICTJLTURE. 



reduced before ignition in order that substantially all of the potash 

 might 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 (KjO) 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. 









Amount 

 K2O ex- 



Proportion 



Amount of 



Sample 



Degree of 



Total 



of total 



water re- 



number. 



fineness. 



E2O. 



KiO pres- 



quired for 











ent. 



extraction. 





Mesh. 



Percent. 



Per cent. 



Percent. 





12a 



60 to 100 



10.56 



10.25 



97.06 



160 



126 



100 to ISO 



10.56 



10.45 



98.96 



160 



12c 



ISO and 

 finer. 



10.56 



10.33 



97.86 



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 wiU 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 aU of the ingredients of alimite (with the exception 



