RECORDS OF MEETINGS 425 



some of wjiicli this component appeared in particularly favorable develop- 

 ment, proves calcium hydrate to be pseudo-hexagonal and pseudo-uniaxial. 

 It is actually biaxial, with a Yery small optic angle, possesses good basal 

 <?leavage, and is probably monoclinic in crystallization, being strikingly 

 similar to the micas in form. 



It seems to be further demonstrated that the amorphous constituent 

 itself is variable in character, differing in different cements, and the de- 

 "parture from what may, for the moment, be called the normal, is appar- 

 •ently a function of its inability to resist the action of agents of disintegra- 

 tion; this interpretation is tentative, however, pending further investi- 

 -gation. It follows, from this, that the amorphous constituent should be 

 interpreted with caution, the mere fact of its presence not being sufficient 

 to indicate that the cement in question would be suitable for use in 

 situations exposed to the action of water. 



It also seems apparent that the character and development of this con- 

 stituent is affected by the quantity of water used in making the concrete, 

 ^nd possibly by other factors not yet determined, so that its formation 

 may be partially or even completely suppressed, leaving relatively large 

 amounts of primary crystalline calcium hydrate unchanged — a condition 

 which renders the concrete extremely susceptible to the action of various 

 agents of disintegration. 



Defective concrete, taken from actual structures, the disintegration of 

 ■which was traced to this cause, was briefly discussed. 



The paper proved of exceptional interest and elicited much favoral^le 

 -criticism. Dr. George F. Kunz, Mr. Nathan Johnson, Mr. Charles TToad- 

 ley, Mr. Benjamin Howes, Professor I. H. Ogilvie, Mr. F. K. Morris, 

 Professor G. I. Finlay and Professor C. P. Berkey participated in a dis- 

 <3ussion to which more than thirty-five contributions were made. 



The Section then adjourned. 



Douglas W. Johnson", 



Secretary. 



BUSIN'ESS MEETING 

 11 October, 1915 



The Academy met at 5 :30 p. m. at the American Museum of Natural 

 Histor}^, President George F. Kunz presiding. In the absence of the 

 Eecording Secretary, Dr. H. E. Crampton was appointed Acting Record- 

 ing Secretary. 



The minutes of the last business meeting were read and approved. 



