PROPERTIES OF PORTLAND CEMENT. 391 



test and yet develop unsoundness if the set is quickened by the use of 

 more or less plaster; so much sintered lime remaining unslaked in the 

 quick-setting cement as to cause unsoundness in the accelerated test. 

 For the same reason plastered, nonseasoned cements have been en- 

 countered which have developed unsoundness in the steam test, but which 

 remained sound when no plaster had been added. 27 



These facts will more fully be discussed in another part of this paper. 

 We mention them here in order to emphasize the limitations of the 

 soundness test as a test for free lime. 



However, taking all factors into consideration it seems as if the follow- 

 ing conclusions would enable us more accurately to interpret the relation- 

 ship between free lime and soundness. 28 



1. Slaked lime will not cause unsoundness in the soundness test. 



2. ISTonsintered lime must be present in quantity to cause unsoundness ; 

 and if it is so present, the disruption is likely to occur in water and air, 

 as well as in the steam pats. 



3. If both sintered and nonsintered lime are present, the pat may be 

 sound in air and in water, but it is very liable to disintegrate during the 

 hot tests. 



■i. Fused or sintered lime, in the absence of non-sintered lime, in- 

 dicates a hard-bumed cement which in all probability contains ' an 

 abundance of material having strong cohesive properties. The effect of 

 such lime upon the soundness is therefore a quantitative consideration. 

 Sintered lime, unless present in large amounts, will not cause disrup- 

 tion in air and water pats, but even a fair amount is liable to cause 

 unsoundness in accelerated tests. The effect of a small amount is not 

 liable to become apparent to the eye. 



5. Fineness assists the soundness. 



Conditions of the experiment recorded in Table VIII. — These conclusions were 

 applied to the microscopic examination of the duplicate samples of the twelve 

 cements sent to Professor White. The source of each samples was first disguised 

 from the operator in order to eradicate any knowledge of the physical properties of 

 the cements until after the predictions from the microscopic examinations had 

 been made. Table VIII includes Professor White's diagnosis of these cements, as 

 well as our microscopic and sieve tests of fineness. 



-'' It is known that manufacturers sometimes test the soundness of their cement 

 before the plaster has been added and that this practice has caused the shipment 

 of unsound material. 



28 Table VI records phenomena which under certain conditions may impose 

 even greater limitations to these interpretations. It imposes a condition, however, 

 which is almost negligible in practical cement manufacture, namely: the aeration 

 of ground cement in very thin layers. In commercial cements the percentage 

 of free lime which will not react with the test solution because of a coating 

 of carbonate, is usually insignificant. 



