740 
PROCEEDINGS OF SECTION H. 
— 
Weight of 
Slabs. 
Slab 
and Glue. 
Glue taken 
up. 
Glue, 
Per Cent. 
Plaster, No. 1 
Keen’s Cement, No. 2 
Grs. 
Grs. 
Grs. 
; 
7,580 
8,830 
1,250 
16*5 
8,030 
8,200 
170 
2*1 
Portland and Sand, No. 3 
8,460 
8,710 
250 
2*9 
Portland, No. 4 
10,090 
10;280 
190 
1-8 
RELATIVE ROUGHNESS OF SURFACES OF THE PLASTERS. 
Tests were hardly necessary since the different degrees of rough- 
ness were quite apparent to the eye and touch, but the following- 
experiments were made to obtain, if possible, numerical values for 
roughness. The surfaces were well rubbed in with red lead to represent 
ordinary dust and dirt. .Red lead was chosen because it is heavy and 
renders the increase in weight more appreciable ; and, secondly, because 
the adherent pigment is at once apparent, and the depth of colour 
shows the relative amount of powder retained by the roughness of the 
surface. 
— 
Weight. 
Plus 
Red 
Lead. 
Increase 
in 
Weight. 
Plaster, No. 1 
Keen’s Cement, No. 2... 
Portland and Sand, No. 3. 
Portland, No. 4 
Grs. 
7,415 
8,080 
8,520 
9,905 
Grs. 
7,420 
8,080 
8,530 
9,910 
Grs. 
5 
0 
10 
5 
per 72 inches superficies. 
or twice as much as Nos. 1 and 4. 
Again, so as to make the surface take up as much as possible, the 
red lead was rubbed in and the excess scraped away with a cork, and 
the loose powder blown off, when the following numbers were obtained 
for the two rougher materials; it was thought unnecessary to make 
further trials with the other two : — 
Portland and Sand, No. 3 
Portland, No. 4 
Grs. 
8,520 
9,910 | 
Grs. 
8,600 
9,915 | 
Grs. 
80 
5 
or 16 times as much as No. 4. 
After rubbing off as much of the red lead as possible by means of 
a dry cloth, the Keen’s cement was of a pale-orange colour, the 
plaster of an orange colour, the Portland of a red colour, and the 
half Portland of a bright-red colour. 
These colours agree with the roughness apparent to the eye and 
to the touch in the following order: — Keen’s, plaster, Portland, half 
Portland, this last being the roughest of all. 
CONCLUSION. 
Prom the foregoing experiments Keen’s cement appears on the 
whole to be the best for indoor work, but it is not adapted for outdoor 
use unless painted, since it is to a certain extent soluble in water. It 
takes up less water, less organic matter as represented by the glue, 
than others, and practically no dust ; further, it is more resistant to 
the action of crystallising sodium sulphate; but Portland cement, if 
painted, would be even superior to it on account of its greater hard- 
ness and durability. 
