477
CEMENT.
The specific gravity of loose material which was spread out in layers 1 inch thick and exposed to the air in a dry, cool storehouse, was found as shown in the next table.
Remarks.
Specific
gravity.
Class.
Brand.
After 14 days’ exposure to the air. After 28 days’ exposure to the air. After 14 days’ exposure to the air. After 28 days’ exposure to the air. After 14 days’ exposure to the air. After 28 days’ exposure to the air. After 14 days’ exposure to the air. After 28 days’ exposure to the air. From a barrel about 10 years’ old. Do.
3.09
3.08 3.06 3.04
3.09
3.09
3.03
3.04 2. 82 2. 75
Portland
....do...
....do...
....do...
....do...
....do...
Natural .
----do...
----do...
----do...
Star, with plaster....
Star, without plaster_
Whitehall.............
Newark and Rosendale .
Norton................
Not known.............
After heating the material to 110° C. and to redness the results were as follows:
SPECIFIC GRAVITY AND LOSS IN WEIGHT UPON HEATING.
Loss in weight.
Specific gravity.
After heating to redness.	Upon heating to 110° C.	Upon heating to redness from 110° C.	Remarks.
3.15	Per cent. 0.14	Per cent. 0.61	Fresh material from
			barrel.
3.18	0.19	2.11	Exposed to air 14 days.
3.16	0.52	2.06	Exposed to air 28 days.
3.17	0.20	0.80	Fresh material from
3.18			barrel.
	0.22	1.96	Exposed to air 14 days.
3.15	0.45	1.74	Exposed to air 28days.
3.15		0. 59	Fresh material.
3.19	0.30	1.85	Exposed to air 14 days.
3.23		2.25	Exposed to air 28 days.
2.91	0.15	2.53	From barrel.
3.00	0.13	22.24	Do.
3.16	0.	4.58	Do.
3.15	.20	6.86	Exposed to air 14 days.
3.14		7.20	Exposed to air 28 da vs.
3.03		«9.10	About 10 years old.
3.07		«10.60	Do.
Brand.	Original condi- tion.	After heating to 110° C.
Star, with plaster..	3.12	3.13
	3.09	3.09
	3.08	3.07
Star, without plas-	3.13	3.15
ter.		
	3.06	3.09
	3.04	3.04
	3.13	
	3.09	3.08
		3.09
Cathedral		2.83	2.84
Silica		2.87	2.89
Newark and Ro-	3.06	
sendale.		
	3.03	3.04
		3.04
	2.82	
Unknown 		2.75	
		
«Total loss in heating from atmospheric temperature.
h rom the above it appears that drying at 110° C. does not materially change the specific gravity of the material, but heating to redness restores the cement to its primitive value as it came from the barrel, or raised it above the value found in the first determination. The losses in weight upon heating are shown in the above table, and it will be seen that the most marked changes in specific gravity are accompanied by corresponding losses in weight. The large loss in weight upon heating the Silica cement to redness is attributed to the presence of crushed limestone, which the manufacturers state formed 60 per cent of this product.
Determinations were made on material which had been mixed with water, set different intervals in air or in water, and reground to pass