176 



RBIBLING AND SALINGER. 



test is of great value under certain conditions. Every good Portland 

 cement will meet its requirements before or after ignition, and therefore 

 its determination ini2:»oses no unjust or partial test. 



Determination of the specific gravity will be valueless unless the efEects 

 of aeration are guarded against, as the exjDosure of the small quantity 

 of cement necessary for this test enables the action of the atmosphere 

 to alter its composition very much in a short time and so to reduce its 

 specific gravity accordingly. 



It is the practice of this laboratory to take the cement for the specific 

 gravity determination from the sample at the same time that the material 

 for the other tests is taken. It is then dried at 110° for thirty minutes 

 and immediately put into small, glass bottles which are tightly corked 

 until the cement has cooled ; it is only used after this procedure. 



The difference between the specific gravities before and after ignition 

 indicates the amount of volatile constituents present in the cement, but 

 when it is desired to know only the amount of carbonic acid and combined 

 water which has been absorbed, the loss on ignition afiiords a much 

 simpler and a more accurate test. 



CLIMATIC INFLUENCES. 



Local, tropical, climatic conditions must necessarily have an influence 

 upon cement and cement testing. In the tropics, all work is done 

 practically in the open air, being protected only from the direct rays of 

 the sun. The climatic conditions under which cement tests or commercial 

 work are undertaken coincide very closely with the meteorologie obser- 

 vations which are given in the following table for the year : 



Table XXV^I. — Summary of meteorologie observations taken at Manila," P. I., 

 situated on the west coast of the Island of Luzon. 



Month. 



Temperature. 



Mean 

 relative 

 humid- 

 ity. 



Aver- 

 age 

 rain- 

 fall. 



Aver- 

 age 

 num- 

 ber of 

 rainy 

 days. 



Mean 

 cloud- 

 iness. 



Per ct. 



Mean. 



Maximum. 



Minimum. 





°C. 



op. 



°C. 



°F. 



°V,. 



°F. 



Per ct. 



In. 





January 



25 



Ti 



33.9 



93 



16. 7 



62 



78 



1.19 



5 



4.6 



February 



25.5 



78 



35.(1 



96 



16.1 



61 



74 



.41 



3 



3.8 



March 



26.6 

 26.3 

 26.3 

 27.8 



SO 

 83 

 83 



82 



35.6 

 37.2 

 37.8 

 36.1 



96 



99 



100 



97 



17.2 

 18.9 

 21.7 

 21.7 



63 

 66 



71 

 71 



72 

 71 

 77 

 82 



.74 

 1.14 

 4.20 

 9.62 



3 

 4 

 9 

 16 



3.8 

 3.5 

 5.1 

 6.8 



April 





June 



July 



27.2 



81 



35 



95 



21.1 



70 



85 



14.57 



21 



7.5 



August 



27.2 



81 



34.4 



94 



20.6 



69 



84 



13.87 



20 



7.5 



September 



26. G 



80 



34.4 



94 



21.1 



70 



86 



14.93 



20 



7.4 



October 



26.6 



80 



35 



95 



20.6 



69 



83 



7.54 



16 



6.1 



November 



26.1 



79 



33.3 



92 



18.3 



65 



82 



5.13 



12 



5.8 



December 



25 



77 



33.3 



92 



15.6 



60 



81 



2.13 



8 



5.6 



a"The climate of Manila is hot and moist during the greater part of the year. During the spring 

 months it is dry. The afternoon temperature of the hottest portion of the year is modified by the 

 northeast trade winds that prevail at that season." Brewer, Isaac W.: Personal Hygiene in Trop- 

 ical and Semi-Tropical Countries (190S), 119. 



