142 



REIBLING AND SALINGER. 



The literature on the subject of cement is tilled with information on tlie effects 

 of aeration." Cements high in lime or those which are '"unsound" due to the 

 presence of free lime, are improved by exposure to the air, but cements higli in 

 alumina, especially if lightly burned, are apt to become quick setting and 

 otherwise dangerous under the same treatment. This is especially true in the 

 tropics as "aluminous cements are readily subject to alteration in surrouiulings 

 exposed to alternate dryness and humidity and also when exposed to a higli 

 temperature." '" 



Cements are encountered, tlie lineness and soundness of which may be very 

 satisfactory throughout, but the specific gravity, time of setting and tensile 

 strength (the 1 to 3 mortar especially) may vary from one extreme to the 

 other. None of the pats may warp or disintegrate, even during steam and air 

 exposures, so that perfect soundness may be a characteristic of such material. 

 In fact, it is possible for a pat to remain at a red heat for several hours before 

 it disintegrates in any marked decree. Cement of this class, according to cliemical 

 analysis made from time to time, proved itself to have a uniform composition in 

 all respects except tlie loss on ignition, which varied from 1 to 6 per cent. The 

 silica content was vmiformly low and the alumina and iron high. It is hardly 

 necessary to add that every known precaution was taken to secure uniform 

 results. 



ExiDerience in this laboratory has demonstrated that in most instances 

 variations sncli as "those mentioned are encountered in cement samples 

 wliieli have been received in tliin paper 1)ags, or which had otherwise 

 been exposed to the air; and that cement received for testing in closely 

 covered cans and boxes and not subseqriently exposed to the air, nsually 

 gave very acceptable, uniformly good results. These conclusions are 

 emphasized Ijy the following tables : 



Table II. — Characteristic examxdes of tests of cement slored in cnns." 



Sample No. 



Mortar 



1 to3. 



Sample No. 



Mortar 



1 to 3. 



T-day. 



28-day. 



7-day. 



28-day. 



D5-2 



240 

 210 

 210 

 193 

 210 



289 

 265 

 305 

 300 

 315 



BB13 



225 

 238 

 205 

 212 

 248 



307 

 295 

 299 

 260 

 288 

 i 



D5-4 



BB14 - 



D5-6 



BB15 



D.">S 



BBIG 



D5-10 



BB17 







"Meade: Chem. Eng. (1907). 5, 341; Taylor and Thompson: Concrete. Plain 

 and Reinforced, New York (1907), 62; Spalding, Frederick C. : Hydraulic Cement. 

 New York (1904), 4, 50, SO; Candlot, il.: Cement et Chaux Hydrauliques. Paris, 

 1891. 



'"Spalding, Frederick C: Hydraulic Cement. New Y'ork (1904), SI. 



"The setting time in all of these cements was satisfactory and uniform. 



