PROPERTIES OF PORTLAND CEMENT. 



375 



of this solution would contain only enough water completely to hydrate 

 about 0.67 milligram of calcium oxide. This difference is apparent in 

 the microphotographs shown by figures 2 and 3 and is also evident from 

 the data recorded in Table I. 



Table I. 



-The effect of water upon the length of calcium hydroxide-phenol crystals 

 formed on the microscopic slide. 



Number of 

 drops of 



water 

 added to 

 the anhy- 

 drous 

 phenol 

 solution. 



0.0° 



0.0 



1.0 



4.0 



7.0 



Percent- 

 age of 



water in 

 the test 



solution. 



0.0 



(") 

 0.40 

 1.60 

 2.80 



Length of crystals, in milli- 

 meters, produced in the 

 thin sections of slides. 



From calcium 

 hydroxide 

 [Ca(OH) 2 ]. 



From calcium 

 oxide (Cao). 



No crystals. 

 0. 06-0. 12 0. 01.5-0. 03 



0.06-0.12 0.015-0.03 



0. 06-0. 27 0. 015-0. 03 



0. 27-0. 50+ j 0. 025-0. 06 



a The anhydrous reagents were prevented from absorbing water from the air by ringing 

 the cover glass with Canada balsam. The same materials developed crystals in about 

 fifteen minutes if the cover glass was not so inclosed. 



13 Trace absorbed from air. 



Table I shows that crystals from calcium oxide do not grow in a motionless 

 phenol solution containing less than 1.6 per cent of water, to a greater length 

 than 0.03 millimeter. On the other hand, the presence of a mere trace of that 

 reagent was sufficient to cause them to grow from calcium hydroxide in lengths of 

 from 0.06 to 0.12 millimeter. We have not been able under a tight cover-glass 

 inclosed in balsam to produce crystals from calcium oxide longer than 0.270 

 millimeter except by the use of phenol saturated with warm water. This same 

 solution dissolves the crystals if the hydroxide is used; and water saturated with 

 phenol dissolves those formed from both oxide and hydroxide. 



In solutions containing less than 1.5 per cent of water, the presence of a con- 

 siderable amount of oxide tends slightly to reduce the length to which crystals 

 produced from the hydroxide would otherwise grow. 



All of the crystals intermingle freely and retain their characteristic 

 appearance, thus further proving that the final crystalline compounds 

 obtained from both the oxide and hydroxide are chemically identical. 



The difference in the size of the crystals which are formed in slightly 

 hydrated solutions under the conditions imposed by the microscopic test, 

 is due entirely to the fact that the oxide must hydrate before it is able to 

 react with phenol and more water to develop calcium hydroxide-phenol 

 crystals. This tendency toward hydration is so great that phenolization 

 only occurs to a slight extent until water in excess of one-third of the 

 weight of the oxide is available. 



These results make it highly probable that the long, radiating crystals 

 which are shown in White's photomicrograph 20 of a commercial cement, 



20 hoc. cit. (figure 1). 



