EXPERIMENTS UPON THE POROSITY OP PLASTERS, ETC. 739 
— 
After 48 hours’ drying. 
Temp. 69° F. 
After 6 days’ drying. 
+3 
bl) 
© 
£ 
Moisture 
evaporated. 
Moisture 
retained. 
Per cent. 
Weight. 
Moisture 
evaporated. 
Moisture 
retained. 
Per cent. 
Grs. 
Grs. 
Grs. 
Grs. 
Grs. 
Grs. 
Plaster, No. 1 
8,360 
680 
1,820 
217 
7,580 
1,460 
1,040 
13*7 
Keen’s Cement, No. 2 
8,050 
460 
loss 60 
8,030 
480 
loss 80 
Portland and Sand, No. 3 
8,520 
580 
130 
i-5 
8.460 
640 
70 
*83 
Portland, No. 4 
10,190 
510 
360 
3 '5 
10,090 
610 
260 
2-6 
RELATIVE DURABILITY. 
These plasters are intended for indoor use, and thus will not be 
much exposed to the weather ; still a process of disintegration will go 
on, although at a small rate, and it was accordingly thought desirable 
to obtain definite information upon this point. The four slabs, one of 
each kind, were placed simultaneously in a basin of boiling saturated 
solution of sodium sulphate, and allowed to remain in it for seven 
minutes ; they were then taken out and suspended by strings, over 
dishes, to catch any fragments which might separate and fall. 
Plaster, No. 1. — 6,830 grs., fell all to pieces, and was reduced to a 
mud. 
Keen’s, No. 2. — 8,140 grs., apparently unaffected. 
Half Portland, No. 3. — 8,370 grs., loosened at edges. 
Portland, No. 4. — 9,000 grs., apparently unaffected. 
RELATIVE ABSORPTION OF ORGANIC MATTER. 
Next, to ascertain how much ordinary non-crystallisable organic 
matter they would take up, fresh slabs were placed in a vessel of 
hot, weak glue (of the finest quality), and allowed to remain in for 
forty minutes ; they were then taken out, stood on edge, and allowed 
to dry for twenty-four hours. 
— 
Original 
Weight. 
Slab 
and Glue. 
Increase 
in Weight. 
Per cent. 
Increase on 
Original 
Weight. 
Grs. 
Grs. 
Grs. 
Per Cent. 
Plaster, No. 1 
5,960 
7.800 
1,840 
30-9 
Keen’s Cement, No. 2 
8,170 
8,330 
160 
2 
Portland and Sand, No. 3 
8,660 
8,900 
240 
2-8 
Portland, No. 4 
8,760 
8,870 
110 
1-3 
This test was repeated with fresh slabs. This time the slabs 
were left in the glue for two hours, and allowed to dry on edge for 
twenty-one hours ; the greater original weights of this set of slabs is 
due to their having been used in one of the previous absorption 
experiments with water ; the glue also was a trifie stronger than in 
the previous trial. 
