EXPERIMENTS UPON THE POROSITY OP PLASTERS, ETC. 737 
It is noticeable that the sandstone cubes treated with the raw and 
boiled oils returned to their original weights between 3rd October, 
1889, and 7th July, 1890, and again between 12th November, 1890, 
and 4th August, 1892 (the one with blue oil, however, being 1 oz. 
lighter, which may have been partly due to slight chipping and 
weathering) ; but, although they returned to their original weights, 
they do not appear to have completely lost the oil, or its beneficial 
effects, inasmuch as they only took up 1 oz. of water, whereas the 
unoiled cube took up 7 oz. of water. 
2.— EXPERIMENTS UPON THE POROSITY OF PLASTERS 
AND CEMENTS. 
By A. LIVERSIDGE, M. A . , F.R.S., Professor of Chemistry , University of Sydney , 
The series of experiments given in the following notes were 
carried out some years ago with the object of ascertaining which 
would be the most suitable plaster or cement to be used for the 
internal walls of the Prince Alfred Hospital, Sydney, then in course of 
erection. I venture to bring the matter forward, as I am informed 
that the result may be of use to architects and engineers. No tests 
were made as to the permeability of the plasters and cements for air 
and gases ; those interested in that question are referred to the 
researches of Pettenkofer, Marker, Scliuitze, and others. 
RELATIVE PERMEABILITY. 
The trials were in all cases made upon slabs (prepared by a 
skilled plasterer) 6 inches square by i-inch thick, and finished off on 
one surface in the usual way for walls, the other surface being as left 
by the board on which the plaster was worked. The slabs consisted 
of — 
No. 1. Ordinary plaster. 
No. 2. Keen’s cement. 
No. 3. A mixture of half Portland cement and half sand. 
No. 4. Portland cement. 
In the first experiment the slabs were placed in rain-water on 
Saturday, 18th October, and left in soak until Tucsda} r , the 21st. 
The water was observed to most quickly permeate the slab composed 
of half Portland cement and half sand, more slowly through the pure 
Portland, still more slowly through the common piaster (half each 
lime and sand), and most slowly of all through the Keen’s cement. 
The slabs were marked with ink, and it was noticeable that the 
amount of spreading of the ink (as on blotting-paper) followed the 
same order as the permeability of the slabs to water. 
The slabs were taken out of the water on Tuesday, the 21st, after 
being in soak for fifty-eight hours — i,e. } from 12*30 p.m. on Saturday 
till 10*30 a.m. on Tuesday. They were stood on end and allowed to 
drain for ten minutes, and then wiped dry and weighed. 
