9 



This shows that all the constituents of pure feldspar-lime clinker 

 lie between the limits allowable in a good Portland cement, and 

 that ferric oxide is the only necessary constituent absent. If com- 

 mercial feldspar and lime were used, however, this would no doubt 

 also be supplied in sufficient quantity, and at the same time the 

 silica and lime would be reduced more closely to the mean of that 

 found in a good Portland cement, providing the feldspar does not 

 contain an excessive amount of free silica. 



In order that a clay may be suited for the manufacture of cement 

 it should have a percentage ratio of silica to alumina of from 3 to 1 

 to 4 to I. 1 The ratio of these two constituents in feldspar is 3.5 to 1. 

 In muscovite and leucite of theoretical composition the proportion of 

 silica to alumina is less than 3 to 1, but in commercial samples of 

 leucite-bearing rocks the ratio is usually greater than 4 to 1. 



A clinker of the same ultimate composition as that which results 

 when feldspar and lime are heated together may also be obtained 

 when part of the lime is replaced by sufficient calcium chloride to be 

 equivalent to the potash and soda in the feldspar, the total calcium 

 used remaining the same as before. In carrying out this experiment 

 the feldspar and lime were ignited to constant weight as already de- 

 scribed, and the calcium chloride thoroughly dried by heating in an 

 air bath below its melting point. Ten grams of the feldspar were 

 well mixed with 2.0050 grams of calcium chloride and 15.7895 grams 

 of calcium oxide, and the mixture then ignited in an open dish in the 

 furnace at 1400 C. By this treatment the alkalies are volatilized 

 as the chlorides. 2 On igniting for one-half hour the weight lost by 

 the ignited mass amounted to 2.5632 grams, equal to 25.63 per cent 

 of the feldspar. When expressed as the chlorides the percentage of 

 alkalies in the feldspar used amounted to 25.82 per cent. It would 

 appear, therefore, that practically the whole of the alkalies in the 

 feldspar were volatilized during the first half hour of ignition. On 

 continuing the ignition for one hour longer the additional decrease 

 in weight which took place amounted to only 0.0090 gram. The 

 residue was then analyzed for potassium and chlorine, but only a 

 trace of each was found. 



This shows that the volatilization of the potash in feldspar takes 

 place more rapidly when part of the lime is replaced by calcium 

 chloride than when the feldspar is ignited with lime alone, but in 

 each case the ultimate composition of the residue obtained is the same. 

 Any excess of calcium chloride used above that equivalent to the 

 potassium in the feldspar is slowly decomposed at the temperature at 

 which the ignitions were made, leaving behind the oxide of calcium. 



* Bleinlnger, loc. cit., p. 223. 

 *Herstein, J. Ind. Eng. Chem. 8, 426 (1911). 

 [Cir. 71] 



