465
BRICKS.
BKICK.
These bricks were submitted for test by the Engineer Commissioner of the District of Columbia.
There are three series of tests each made on whole bricks and on half bricks. In the first series of each size the compressed surfaces were faced with plaster of paris, according to the usual methods employed at the arsenal. In series (a) the specimens were tested between cardboard cushions, total thickness on each side, while in series (5) pine-wood cushions were used, i” thickness on each side. The cardboard and pine-wood cushions were used at the request of the Engineer Commissioner, District of Columbia. The same test number is used in the tests of whole bricks of a given manufacture, the subletters (a) and (b) referring to the tests with cardboard and pine-wood cushions, respectively.
The tests of the half bricks are designated in the same manner.
The average strength of the several groups, omitting from the comparison those samples of whole bricks in which there were no representatives in series (b) and comparing whole and half bricks of the same manufacture, are as follows:
Résumé of results.
	Mean	Relative
	strength.	strength.
Tests of whole bricks:		
Set in plaster		9,060 7,380 5,480	100 81 60
Cardboard cushions			
Pine-wood cushions			
Tests of half bricks:		
Set in plaster		5,640 4,430 4,540	100 79 81
Cardboard cushions			
Pine-wood cushions			
		
Comparison of whole bricks with half bricks.
	Whole bricks.		Half bricks.	
	Mean strength.	Relative strength.	Mean strength.	Relative strength.
Set in plaster		6,990	100	5,640	81
Cardboard cushions		6,150	100	4,430	72
Pine-wood cushions		4,420	100	4; 540	103
An examination of the details of the tests shows four individual cases in which the whole bricks between cardboard cushions surpassed the strength of bricks of the same manufacture which had plastered surfaces. Those tested between pine-wood cushions in every case were found below the corresponding plastered samples.
The half bricks with plastered surfaces surpassed individually those tested between cardboard cushions, but among those tested between pine-wood cushions there were instances of higher strength in the latter series.
raking the general results, the superiority of the plastered specimens as a whole is apparent.
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