483
CEMENT.
for the finer parts of the cements in the case of the Portlands. With the natuial cement in the hydrated state the coarse grains showed the lowest specific gravity in two determinations. The tendency of the coarse grains of this class of cement to retain considerable of the finer mateiial on their surface prevented the more complete grading which was accomplished with the Portlands.
SRECIFIC GRAVITY DETERMINATIONS on material of different sized grains in EEGROUNWM^ERlSIAFTER׳mSaNG1VnTHAWATEkGRADED BY SIFTING, AND ON
[Reground material was dried off at 110° C. before making the determinations.]
Specific gravity after remixed 5 days additional.
2.88 2.87 2.82 2.79 2.61
2.62 2.67 2.64
Loss in weight on heating to redness from 110° C.
Per cent.
5.0
6.0
6.4
6.4 13.0
3.0 2.8 3.2
3.8
11.8
9.0
8.9 9.8
			Specific gravity.		
Brand.	Size of grain.	Original condi- tion.	Mixed 30 minutes.	Mixed 5 days.	After heating to redness.
Star		Inch. >.0058	3.09	3.04	2.94	3.09
	. 0050		3.04	2.94	3.14
	.0034	3.12	3.10	2.90	3.11
	.0027	3.12	3.06	2.89	3.09
Alsen		<. 0027	3.04	2.72	2.68	3.04
	>.0058	3.07	3.02	2.92	3.09
	.0050	3.12	3.08	2.97	3.05
	.0034	3.08	3.05	2.93	3.00
	. 0027	3.09	3.05	2.89	3.09
Hoffman		<.0027	2.99	2.83	2.37	
	>.0058	3.08	2.73	2.75	3.10
	.0027	3.00	2.96	2.92	3.17
	<. 0027	3.02	2.86	2.82	3.12
The incompleteness of the change in specific gravity in the early stages after mixing, shown in the preceding table, is further illustrated in the following tests made with different sifted grades of another ?''kich was treated by heating in water, at the temperature of 100 C. for periods of 1, 6, and 24 hours, then dried to a constant weight ot 110- C., and the specific gravity determinations then made:
Brand.	Size of grain. f	Specific gravity.			
		Before hydration.	After heating in water—		
			1 hour.	6 hours.	24 hours.
Whitehall		From the barrel		3.12 3.15 3.07 3.14			
	>.0058 inch	 .0027 to .0058 inch	 <.0027 inch			3.01 2.81 3.07	2.91 2.44 2.84	2.83 2.35 2.55