8 



for several hours. One gram of the feldspar and 1.68 grams of cal- 

 cium oxide, equivalent to 3 grams of calcium carbonate, were then 

 well mixed and ignited in an open dish in the furnace at 1,400 C. for 

 one hour. The weight of the mixture was found to have decreased 

 by 0.1606 gram, which is equal to 16 per cent of the feldspar. The 

 residue was then analyzed for potassium, but only a trace was found. 



The experiment was then repeated, using ten times the amount of 

 feldspar and a corresponding amount of calcium oxide. The same 

 care was taken as before to reduce each constituent to constant weight 

 before mixing. After igniting for one-half hour the loss in weight 

 of the mixture amounted to 1.3912 grams, equal to 13.9 per cent of 

 the feldspar. On repeating the ignition for one hour a further loss 

 in weight of 0.1630 gram took place, which was increased to 0.1768 

 gram on igniting for one hour longer, making a total loss of 1.5680 

 grams, equal to 15.7 per cent of the feldspar. Since the feldspar was 

 shown by analysis to contain 15.9 per cent of K 2 O+Na 2 O, it would 

 thus appear that the greater part of the alkalies in the feldspar were 

 driven off in the form of oxides. This was confirmed by an analysis 

 of the residue, which contained less than 0.2 per cent of total alkalies. 



The hardened mass remaining after ignition strongly resembled 

 cement clinker, and that the product, obtained by igniting feldspar 

 and lime together contains all the essential elements of a cement is 

 well known. Using the feldspar and lime in the proportions of 1 

 to 1.68, a clinker approaching the composition of Portland cement is 

 obtained. 



* 



Thus, if 1 part of feldspar assumed to contain the theoretical 

 amounts of potash, alumina, and silica loses the first-named con- 

 stituent, amounting to 0.17 part when ignited with 1.68 parts of cal- 

 cium oxide, or 3 parts of calcium carbonate, then the clinker which 

 remains will equal 2.51 parts, and will have the percentage compo- 

 sition given in Table III. In the second and third columns are also 

 given the minimum and maximum limits of the constituents of good 

 Portland cement. 1 



TABLE III. Comparison of the composition of feldspar-lime clinker with that of 



Portland cement. 



[Clr. 71] 



1 Bleininger, Bui. Ohio Geol. Survey, No. 3, p. 197 



