NOTES ON A BLOCK OF PORTLAND CEMENT. 
305 
itself. Analysis of this whitish outer skin revealed the fact that the 
lime therein contained was almost wholly in the state of carbonate, 
yielding 35 per cent, of CO„ while the inner portion of the block 
contained only from 2 per cent, to 5 per cent., varying in the lesser 
degree as the interior was reached. On the outside the decomposition 
of the silicate of lime into carbonate had formed a covering which 
effectually protected the inner part from the further action of the 
CO, of the atmosphere, and of the water which, with almost every 
shower of rain, beat upon or surrounded the block periodically for 
years. 
The following are the figures obtained on analysing the substance 
of the inner portion of the block : — 
Total loss on ignition 
... 16 67 
per cent. 
Loss at 100° C. 
... 5-80 
a 
Total OH, 
... 1467 
a 
OH, of hydration ... 
... 8-87 
a 
CO,... ‘ 
... 200 
a 
Total CaO ... 
... 50-96 
a 
EreeCaO 
... 12-65 
a 
SiO, 
... 20-30 
it 
Fe,0 3 
... 240 
it 
Al.O. 
... 4T0 
it 
CaSO, 
... 402 
a 
CaS 
*27 
a 
MgO 
Specific gravity, 2 326. 
•40 
tt 
Upon calculating the above result, water free, the composition of 
the cement before hydration took place was found to be as follows: — 
SiO, 
... • 
. • .. , 
24*36 per cent. 
Fe,0, ... 
... , 
• • ... 
2-88 
A1,0 3 ... 
• • • • 
492 
So 3 
... . 
. ... 
2*83 
CaS 
• • • • 
. ... 
•32 
MgO 
• • • • 
• ... 
•48 
CO, alkalies, 
&c. (by difference) 
2*56 
CaO 

• • t • 
61*65 „ 
10000 
These figures agree closely with those obtained from old samples 
of cement made in England, and analysed from time to time. 
An interesting point in the analysis of the block is the quantity 
of free lime therein stated. Almost the whole of this free lime was 
found to be soluble in water, and throughout all portions of the block, 
except at the outside, the alkaline reaction was well marked. One- 
fourth of the total lime present existed in a conditiou extremely liable 
to be converted into carbonate, and yet during the greater part of half 
v 
j 
