10 



Since the clay used in making cement contains in some cases as 

 high as 3 or 4 per cent of potash, it might be expected that part would 

 escape from the kiln and be collected with the flue dust, particularly 

 in those plants where the Cottrell process for collecting dust had been 

 installed. This has been observed by several investigators to really 

 take place, and the potash then collected is found to be in the soluble 

 form. By the substitution of feldspar for clay in the manufacture 

 of cement the potash then collected would, no doubt, be greatly in- 

 creased, but since the analyses of cement show the presence of alkalies, 

 it follows that with the style of kilns now in use all the potash in 

 feldspar could not be made available in this way. That a larger pro- 

 portion of the potassium would be volatilized by substituting for a 

 part of the lime sufficient calcium chloride to be equivalent to the 

 potassium is evident from the experiments already referred to, and 

 experiments are now being undertaken on a large scale to compare 

 the practicability of this procedure with the simple ignition of feld- 

 spar and lime alone. 



According to the census report for 1910 the Portland cement manu- 

 factured in the United States during the year 1909 amounted to 

 65,000,000 barrels, or 13,000,000 tons, valued at approximately 

 $53,000,000. The maximum quantity of potash which it would be 

 possible to obtain by the use of feldspar in the manufacture of this 

 quantity of cement can be calculated if the potash content of the 

 feldspar is known. This varies up to about 16 per cent, but if half 

 of this, or 8 per cent, be taken as the average percentage of potash 

 in commercial feldspar then 1 part of feldspar combined with 3 parts 

 of calcium carbonate, equal to 1.68 parts of calcium oxide, would yield 

 0.08 part of potash and 2.6 parts of cement. Therefore 13,000,000 

 tons of cement would produce 400,000 tons of potash. Again, quot- 

 ing potash at 66 cents a unit, this would have a value of $26.400,000, 

 which is three times the value of the potash salts used in this country 

 during the year referred to, and about twice the value of the imports 

 for 1911. Whether or not this would cover the cost of the feldspar, 

 its transportation, and the expenses incident to the recovery of the 

 potash can only be determined by experimentation on a large scale, 

 but the probability that potash salts can thus be obtained in large 

 quantities as a by-product makes this method of getting at the potash 

 in feldspar quite promising. 



[Cir.71] 



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