PROPERTIES OF PORTLAND CEMENT. 



377 



The plumes are composed of a more or less compact mass of fine, slender 

 crystals, each individual of which is similar in size and appearance to those 

 developed from fine particles of nonsintered calcium oxide. They develop from 

 certain points on the surfaces of particles of considerable size which form their 

 nuclei and may be desintegrated and their component parts made more apparent 

 by moving the cover glass after they have formed. The first needles formed are 

 pushed out into the surrounding liquid by those which follow. The cover glass 

 forces the liberated crystals to spread in the direction of least resistance and in 

 so doing they cluster into flat groups. The fine, slender crystals which compose 

 these aggregates give to them their characteristic feathery appearance. 



There appear to be points or spots on the surfaces of sintered or fused 

 particles of lime which are most easily attacked by the test solution. We 

 can assume that a fracture, abrasion, or point less heated than others would 

 more easily be hydrated than smoother surfaces, and that such places would be 

 the first to be attacked by the water' in the test solution. The hydration of 

 the lime causes it to swell and to push the crystals into the surrounding liquid. 



Calcium hydroxide when it is formed by small quantities of water 

 acting on sintered particles of lime is crystalline and can be seen in 

 polarized light through crossed nicols, the whole cluster thus becoming 

 visible. The crystals on the outer edges are acted upon by phenol more 

 rapidly than the 

 others and thus 

 feathery fringes, 

 which are character- 

 istic of the plumes, 

 are formed. This is 

 shown by the follow- 

 ing experiment : 



Lime which had been 

 heated in the electric 

 arc was allowed to react 

 with a slight excess of 

 water, thinly spread over 

 the surface of a micro- 

 scopic slide. This slide 

 was dried in a desic- 

 cator without exposure 

 to carbon dioxide and 

 then carefully covered 

 with nitrobenzol and a 

 cover glass. It was 

 then examined in po- 

 larized light through 

 crossed nicols. The result is shown by figure 4, which is a photomicrograph of the 

 crystals formed in this manner. The skeleton outline of plume-like forms, which 

 subsequently become so plain after adding phenol and water, can readily be seen. 



Fused lime will act in a manner similar to the sintered body, with the 

 difference that the crystals would develop much more slowly. Therefore 

 the appearance of plume-like crystals is a positive indication of rather 



Fig. 4.- 



-Grystalline calcium hydroxide obtained from sintered 

 lime. 



