491
CEMENT.
If the carbon dioxide displaces a certain amount of water in the conversion of the hydrate to the carbonate of lime, as represented in the equation—
Ca(0H)2+C02 = CaC03+H20
the equivalents in water for the differences above shown become 0.31 per cent for the Star, and 0.33 per cent for the Storm King.
Determinations were made on the changes in weight during aging, and upon the subsequent heating of a cake of cement, w׳hich was set in the air 36 days. Fifty grams of Whitehall cement were used mixed with 15 grams of water—that is, 30 per cent of the cement by weight, or in the mixture the percentage of water becomes 23.1 per cent. At the end of the above period of time the cake was ground to pass a No. 40 sieve, and the determinations then made. The following table shows the changes in weight during aging:
Age.	Weight.	Loss in weight.		Age.	Weight.	Loss in weight.	
		Total.	Successive.			Total.	Successive.
Days.	Grams.	Grams.	Grams.	Days.	Grams.	Grams.	Grams.
0	65.000	0.	0.	12	57.996	7.004	.065
1	62.560	2.440	2.440	14	57.786	7.214	.210
3	59.850	5.150	2.710	17	57.576	7.424	.210
5	59.070	5.930	.780	20	57.524	7.476	.052
6	58.859	6.141	.211	24	57.403	7.597	.121
8	58.220	6.780	.639	33	57.319	7.681	.084
10	58.061	6.939	.159	36	57.207	7.793	.112
The loss in weight of the mixture during aging is shown to be 11.99 per cent. Of the above material 30 grams were heated from atmospheric temperature to redness, showing a loss in weight of 3.836 grams = 12.79 per cent. Using about a gram in weight of the same material, a determination showed the total loss on heating to redness as before, 12.81 per cent, of which 9.89 per cent was water and 2.92 per cent carbon dioxide.
THE TIME OF SETTING.
The interval of time during which the cement is said to set was determined according to two methods, the Gillmore method and a German method. According to the former, two periods are noted, initial set, when the cement pat will sustain a needle TV" diameter, loaded to weigh 1 pound, thus giving a pressure of 46 pounds per square inch, and the time of final set, when it will sustain a needle yy׳ diameter, loaded to weigh 1 pound = 733 pounds per square inch, each without indentation.
In the latter method a needle ".0444 diameter is employed, loaded to weigh .662 pounds, thus giving a pressure of 427 pounds per square inch, which is used with a pat about 3".15 diameter by 1".575 deep. “The moment at which the needle is no longer capable of completely penetrating the cement pat is considered the beginning of the time of setting. The time intervening between this and the moment when the needle no longer leaves an appreciable impression on the hardened pat is considered the time of setting.”
The results obtained according to these two methods are shown on the diagrams which follow. Different percentages of water were used