PHYSICAL PROPERTIES OF PORTLAND CEMENT. 605 



SPECIFIC GRAVITY. 



8. Significance. The specific gravity of cement is lowered by under- 

 burning, adulteration and hydration, but the adulteration must be in 

 considerable quantity to affect the results appreciably. 



9. Inasmuch as the differences in specific gravity are usually very 

 small, great care must be exercised in making the determination. 



10. When properly made, this test affords a quick check for under- 

 burning or adulteration. 



11. Apparatus and method. The determination of specific gravity 

 is most conveniently made with Le Chatelier's apparatus. This con- 

 sists of a flash of 120 cu. cm. (7.32 cu. inches) capacity, the neck of which 

 is about 20 cm. (7.87 inches) long; in the middle of this neck is a bulb, 

 above and beolw which are two marks ; the volume between these marks 

 is 20 cu. cm. (1.22 cu. inches). The neck has a diameter of about 9 mm. 

 (0.35 inch), and is graduated into tenths of cubic centimeters above 

 the bulb. 



12. Benzine (62 Baume naphtha), or kerosene free from water, 

 should be used in making the determination. 



13. The specific gravity can be determined in two ways: 



(1) The flask is filled with either of these liquids to the lower mark 

 and 64 grs. (2.25 ozs.) of powder, previously dried at 100 C. (212 F.) 

 and cooled to the temperature of this liquid, is gradually introduced 

 through the funnel (the stem of which extends into the flask to the top 

 of the bulb), until the upper mark is reached. The difference in weight 

 between the cement remaining and the original quantity (64 grs.) is 

 the weight which has displaced 20 cu. cm. 



14. (2) The whole quantity of the powder is introduced, and the 

 level of the liquid rises to some division of the graduated neck. This 

 reading plus 20 cu. cm. is the volume displaced by 64 gr. of the powder. 



15. The specific gravity is then obtained from the formula: 



Weight of cement 



Specific gravity = :pr: , Tr , . 



Displaced Volume 



16. The flask, during the operation, is kept immersed in water in 

 a jar, in order to avoid variations in the temperature of the liquid. The 

 results should agree within 0.01. 



17. A convenient method for cleaning the apparatus is as follows: 

 The flask is inverted over a large vessel, preferably a glass jar, and shaken 

 vertically until the liquid starts to flow freely, it is then held still in 

 a vertical position until empty, the remaining traces of cement can be 



