10 BULLETIN 572, U. S. DEPARTMENT OF AGRICULTURE. 
tilized potash with the silicates in the dust. In some plants where. 
coal is used for burning the extent to which the potash occurs in this 
‘‘recombined’”’ form may be considerable, while in certain other plants 
-where oil is used for fuel this combination of the potash occurs in com- 
paratively small amount. In Table II the percentages of the 
different forms of potash occurring in a dust from a plant which uses 
oil for fuel and also from one which uses coal are given: 
Tasie IT.—Percentages of the different combinations of potash in fue-dust samples 
from different sources. \ 
Cement dust from— 
Combination. Riverside] Security 
Per cent..| Per cent. 
Aeid-ansolublepotashs Re O} Jared. tbe ee Pe eS ee er ee eee 0.2 0.5 
Slows, Suliible PULAshie wens. ans ca a PO co BL ee oe ee ee a; 41 
Weatersoluble potashss-.er rae SASS res eee Meee eer ece Pee ee Bee seen 9.8 6.8 
Potala £20 es 44 EP SO ee. ABE oS Oe eee. eee 10.7 11.4 
The determinations of the soluble potash in these samples were 
made by boiling 10 grams of the sample in 500 cubic centimeters of 
water for one-half hour as directed in the Methods of the Associa- 
tion of Official Agricultural Chemists. The insoluble potash was 
assumed to be that portion of the total potash which remained 
insoluble aiter boiling in a 5 per cent solution of hydrochloric acid. 
The difference between the total potash and the sum of the soluble 
and insoluble portions was then taken as the proportion of the 
potash which is slowly soluble m water. 
In a previous publication it was shown, as already stated, that the 
greater part of the potash in feldspar may be made to pass mto solu- 
tion by digesting with lime under a steam pressure of 10 to 15 atmos- 
pheres. In cement dust as it escapes from the kilns the slowly soluble 
and the insoluble potash already are associated with a considerable 
percentage of free lime and consequently it was thought that the 
greater part of these constituents might be recovered in soluble form 
by digesting the dust with steam alone under pressure. This has been 
‘found to be the case, and with the Security cement dust it has been 
‘found possible to recover in this way in soluble form and with little 
increase in pressure upward of 95 per cent of the total potash present. 
If it be assumed, therefore, that it would be practicable to recover, 
or render available, say, 95 per cent! of the potash in the recover- 
able dust of cement plants, then the recoverable and available 
potash escaping from the cement plants of this country amounts 
1 In the case of coal-fired plants it may not be possible, with present commercial apparatus, to render 
soluble as much as 95 per cent of the collected potash, but there is no doubt that as details of commer- 
cial apparatus are perfected this value will represent a fair average for the different plants of the country. 
