380 REIBLING AND REYES. 



more than a trace of free lime when the test was made. Short and long 

 needle-like crystals appeared in all the slides, and plumes in many. 

 Cements which disintegrate were also carefully examined for comparative 

 purposes. They gave a relatively greater number of crystals than the 

 majority of the sound commercial cements, but the distinction is not 

 absolute, because the cements marked "D," "0," "J," and "M," which 

 belong to the class, contained enough free lime to render them indis- 

 tinguishable from unsound cements. 



"We prepared and sealed in test tubes duplicate samples of eight com- 

 mercial cements and four ground by us from the clinker. One set was 

 reserved for future reference and the other sent to Alfred 0. White, who 

 also identified free lime in all of them and classified six as "poor" and 

 two as "passable." He failed to detect a sound and unsound cement of 

 the same brand, • classifying them both as "poor." (See Table VIII.) 



One of us, while at a large manufacturing plant, examined cements 

 which could even withstand the severe Faija boiling test and these also 

 frequently gave an abundance of needles and plume-like crystals when 

 they were subjected to microscopic study. 



The limitations of the test for soundness as an indicator of proper 

 burning were made manifest in the previous publication 24 from this 

 laboratory. To judge by the results given above, it is evident that lime 

 may exist in considerable quantity in some sound Portland cements. 

 Therefore we endeavored to ascertain to what extent the soundness and 

 other properties of Portland cement were affected by various amounts of 

 free lime under different conditions of burning, grinding, and seasoning. 



The following list of observations (Table II), showing the effect of the tem- 

 perature of burning upon the habit of the crystals of calcium hydroxide-phenol, 

 were made possible by an accident to the gearing of a 28.5 meter rotary kiln 

 which enabled one of us to inspect its interior and to collect samples of material 

 throughout its length. These samples were immediately sealed and at a later 

 time examined by means of the phenol test. The shortness of the clinkering 

 zone of this kiln is characteristic of the rotary process. It began at about 5 

 meters and ended at about 1.5 meters from the hot end of the furnace. 



- 1 This Journal, Sec. A (1908), 3, 137-185. 



