306 
PROCEEDINGS OF SECTION B. 
a century this action has been prevented. The existence of so large a 
proportion of free lime in a block of cement which has withstood so 
well the action of time is in itself remarkable. 
All the authorities agree that the setting of cements is due to the 
formation of hydrated silicates, aluminates, and ferrite compounds of 
lime ; and that, in the event of these combinations failing to take 
place properly, the disintegration of cements occurs as a natural 
consequence. 
But in the present instance we have one-fourth of the total lime 
combined with neither the Si0 2 , A1 3 0 3 , nor Fe 2 0 3 , and the cement sub- 
jected to the action of air and water for nearly fifty years yet retaining 
its tensile strength in a marked degree. 
One conclusion to be drawn from this analysis is, I think, that 
the block has been unusually well protected by the outer skin of 
carbonate of lime ; and the presence cf so much free CaO has helped 
rather than retarded the preservation of the block by filling up its outer 
pores. 
The cement, as the water free calculations show, was unmixed 
with any foreign material, and the conditions of setting not therefore 
the same as would hold in ordinary use. 
„ A remarkable fact is that a second block of cement, belonging to 
the same lot as the one which forms the subject of my analysis, was 
found to have its lime contents entirely changed into carbonate, and 
to readily break up on the slightest tapping of a hammer, the two 
blocks having apparently been exposed to exactly the same external 
influences. 
14. — O N A METHOD OF SHORTENING CERTAIN - CHEMICAL 
CALCULATIONS. 
By IF. A. HARGREAVES, M.A., B.C.E. 
In estimating the quantities of gases, it is frequently necessary to 
reduce the volumes to the normal pressure and temperature — that is, 
to a pressure corresponding to a height of 760 millimetres of mercury 
and to a temperature of 0° Centigrade, or, as it is more convenient in 
these calculations to express it, to 273° absolute temperature. Again, 
it may be required to find how many litres (Y) of a certain gas may 
be obtained at a particular time under the ordinary or other pressure 
and temperature of the air, which we may designate as pressure P and 
temperature T (absolute). 
If T be the absolute temperature corresponding to t° Centigrade, 
then T = (273 + t). 
Now, in working out the equation representing the reaction which 
produces the gas, the quantity of gas produced is obtained in grammes 
weight. Two operations are then necessary — first, to convert grammes 
to litres at 0° C. and 760 mm. ; and, second, to reduce the number of 
litres so found to the volume V at pressure P and absolute temperature T. 
In order to do this the text-books give formulae which are, in every 
case that I have seen, difficult to retain in the memory, and more or less 
tedious in application. 
