PROPERTIES OF PORTLAND CEMENT. 373 



pletion and although the crystals may not be pure, still all of the solid has 

 risen to the surface and a sharp line of demarcation is visible. A microscopic 

 examination of the crystals formed in tubes 4 and 5 showed that they resembled 

 each other in all respects. They were similar to those shown by figure 2. 



A more satisfactory and accurate method for tracing the gradual slak- 

 ing of lime and its ultimate conversion into the crystals under considera- 

 tion, is to allow hydrogen gas saturated with water to bubble through 

 chloroform or nitrobenzol containing a slight excess of phenol over and 

 above the amount necessary to bring the calcium oxide into complete 

 reaction. A microscopic examination of calcium oxide treated in this 

 manner shows that the reactions proceed very slowly. 



At first, a gradual hydration of the oxide takes place, which can be noted 

 because the lime when hydrated becomes visible in polarized light through crossed 

 nicols. After the gas has bubbled through the solution for many hours, small, 

 slender crystals begin to appear. These continue to grow in size and number, 

 and the loss by ignition of filtered samples gradually approaches a maximum. 

 Eventually, the crystals resemble those which are developed by a similar process 

 from the hydroxide and if the saturated gas is allowed to continue to bubble 

 through the solution, the loss by ignition of filtered samples decreases until 

 finally they dissolve in the solution. If the latter is then dehydrated, the crystals 

 again appear. It requires very much less saturated gas to produce a maximum 

 yield of crystals from the hydroxide than from an equivalent amount of oxide. 



The crystals have also been separated by us from their solution in an 

 excess of phenol and water. Water gradually was added to the tubes 

 containing the oxide or hydroxide, phenol, and chloroform or nitro-benzol, 

 until the crystals formed had dissolved. The resulting solution was 

 filtered, evaporated over sulphuric acid to crystallization in a vacuum 

 desiccator, the crystals were then washed with chloroform and dried in 

 vacuo. 



Unfortunately, no solvent for recrystallization has been found, and 

 therefore it has been impossible to obtain exactly concordant numbers on 

 analysis. The purest crystals obtained were found to contain from 20.5 

 to 23.8 per cent of calcium oxide. 



The analyses of the purest crystals as well as the conditions necessary 

 for their synthetic preparation, indicate that they have the following 

 composition: Ca(OH) 2 , (C 6 H 5 OH) 2 , H 2 0. 18 



A study of the behavior on the microscope slide of calcium oxide and 

 hydroxide in the presence of phenol containing varying amounts of water 

 confirms these conclusions and gives a method for the positive identifica- 



18 For example, in on<^ instance 0.3280 gram of substance gave 0.0778 gram 

 of calcium oxide and 0.1592 gram of water. A microscopic examination of these 

 crystals showed that they contained a small amount of impurities. If we con- 

 sider these impurities as calcium carbonate and the above formula as the com- 

 position of the pure crystals the theoretical yield of water should have been 

 0.1575 gram, which differs by only 0.0020 gram from that actually obtained. 



