88 THE WOMBAT. 



contained 70% of carbonate of lime. This, on being burnt 

 and ground, set hard under water and gave a proof to 

 Smeaton that the hydraulic properties of lime were due to its 

 containing certain proportions of clay. These were the 

 experiments that formed the foundation of our present know- 

 ledge and method of manufacture of cement and Portland 

 cement. 



About this time Roman cement came into use, and this 

 is nothing more or less than an intermediate lime containing, 

 perhaps, rather an excess of clay. It is made from a natural 

 stone found on the east coast of England near Harwich, and 

 called Septaria. There are large deposits of this stone all over 

 England, and there is a small quantity of it to be found in 

 Port Phillip Bay, at Mornington. Lias lime or Lias cement 

 is another intermediate lime, which probably more closely 

 resembles Portland cement in its constituent parts. None of 

 these natural hydraulic limes were burnt at a high temperature ; 

 they were usually burnt at about the same temperature as 

 ordinary lime. If by any chance any of the material was 

 overburnt, it was thrown on one side as useless, so it was the 

 aim of the burner to get as little overburnt material in his kiln 

 as possible. 



About the year 1824, a bricklayer name Aspdin, of Leeds, 

 carried out a number of experiments with artificial hydraulic 

 lime ; by chance he ground up some of the overburnt parts — 

 pieces which were burnt to a cinder and which, up to that 

 time, everyone had been careful to exclude. He was surprised 

 to find that these pieces not only set when put in water, but 

 that they set infinitely harder than when only burnt to the 

 same degree as ordinary lime. He was so satisfied that he 

 immediately took out a patent for the manufacture of artificial 

 hydraulic lime, and in his specification, when describing the 

 process, he calls it " Portland cement." This is the first 

 mention we have of Portland cement, and this industry, 

 started in so small a way some sixty years ago, is now one of 

 the great commercial industries of the world. In its early 

 days it had many difficulties to contend with, especially from 

 the makers of Roman cement, who opposed it by ever}' means 

 that lay in their power. Cases occurred where it failed to do 

 its work, and in more than one instance it gave disastrous 

 results, houses and walls that were built with it collapsing, 

 until people were suspicious and afraid to use it. However,. 

 difficulties and troubles were one by one overcome, and many 

 engineering feats which have since been executed, could never 

 have been carried through without its aid. 



Portland cement as manufactured to-day is in principle 

 the same as that made by Aspdin, the only difference being 

 in the details, but it is these details which constitute the 

 difference between a good and a first-class cement. The 



