410 REIBLING AND REYES. 



on the market except as hydraulic lime. It would either fail in sound- 

 ness, or if sound, fail to pass the tests of strength and the .other require- 

 ments of the cement specifications. On the other hand, very few 

 commercial cements represent a perfectly sintered product. Underburued 

 cement usually comes to the consumer mixed with the harder, burned 

 material from the same mill. Granted that few manufacturers wil- 

 fully mix a good and a bad cement to give an average material which 

 would pass inspection, yet if their clinker contains underburned cement 

 the result is just the same, to a greater or less degree, according to the 

 fusion products formed. The best stationery kiln process yields a consid- 

 erable amount of underburned clinker. Some manufacturers sort this 

 out very carefully. One efficient method of so doing is to wet the fresh 

 clinker with water for a few days, and then sort or screen out the fine 

 material. The rejected, underburned cement is sometimes prepared and 

 sold as hydraulic lime, and sometimes it is used as a binder for the raw 

 meal bricks and re-burned. 



Other manufacturers do very little or no sorting even when the clinker 

 contains a considerable quantity of bad cement. The more or less non- 

 homogeneous product of their kilns is dumped into covered bins or piled 

 out in the open air and allowed to season for an indefinite time, according 

 to its needs or according to the convenience of the manufacturer. The 

 unsorted, sound and disintegrated products of the kiln are finally crushed, 

 ground into an intimately mixed powder and then packed and sold 

 as Portland cement. The finished product is not true Portland cement, 

 but a mixture of seasoned, underburned and well-burned cement con- 

 taining sintered, nonsintered, and hydrated free lime, and fused and 

 sintered compounds of many kinds. 



One of the authors inspected commercial stationary kilns which to all ap- 

 pearances produced at least 15 per cent of bad clinker, very little of which was 

 afterwards sorted out. Some of the clinkers from these kilns were thoroughly 

 vitrified, some sintered, some underburned and some all three in one. These 

 clinkers were weathered in the open air for from 3 to 5 months before being dried 

 and ground. 



The heaps of clinker which had lain in the sun and rain for about three 

 months presented the appearance of big ash piles. Fully one-half of the 

 material had disintegrated completely, and the whole was covered with a 

 thick incrustation of calcium carbonate stained from gray to reddish- 

 brown and black with various decomposition products. Six samples of 

 the material taken from beneath the outer crust were sealed in cans and 

 shipped to the laboratory for inspection. Figure 15 gives an idea of 

 the contents. 



