THE WOMBAT. 89 



name Portland cement is altogether misleading, and a better 

 term would have been hydraulic or water cement. The name 

 comes from its similarity in colour and texture to a building 

 stone extensively quarried at Portland, in the south of England. 



To briefly summarise the process of manufacture, I will 

 describe the method carried out at Fyansford as being in our 

 immediate neighbourhood. A rich lime containing about 96 % 

 of carbonate of lime is thoroughly and carefully mixed with 

 clay, and water is added for the purpose of moulding it into 

 bricks. These bricks are dried and burnt in kilns until they 

 become vitrified ; the vitrified bricks or "clinker" are ground, 

 and the resulting powder is cement. 



Having roughly gone through the mode of manufacture, 

 we now come to the point when it is delivered to the con- 

 sumer, and also to the time when testing is requisite. 



The tests generally specified are : 



1 st. Tensile strain. 



2nd. Soundness. 



3rd. Fineness. 



4th. Chemical test. 



There are other tests, perhaps as equally important, but 

 these four are the commonest. 



The first test is carried out by making briquettes, which 

 have a sectional area of one inch in the smallest part. These 

 briquettes have to stand a breaking strain of 35olbs. in 7 days, 

 and 55olbs. in 28 days. Some engineers require only 3oolbs., 

 while others demand 40olbs. in 7 days, but 35olbs. and 55olbs. 

 will represent a fair average of the standard requirements. 

 •Care and manipulation are requisite in making briquettes, and 

 J am sorry to say that instances have come under my notice 

 in this colony where so-called experienced testers have not 

 been able to get a breaking strain of one single pound out of 

 a briquette, while, with proper handling, briquettes made 

 from the same bulk, on the same day, in the same room, and 

 with the same appliances gave a strain of over 40olbs. 



Briquettes are made in the following way : — the cement 

 is gauged with a minimum of water, say from 15% to 20%, and 

 it is put in brass moulds with all speed : the more quickly this 

 operation is performed the better will be the results. For the 

 first 24 hours they are covered with a damp cloth or put in a 

 zinc-lined box — in any case they must not be put in the sun, 

 or wind, or before the fire, so that the moisture can be dried 

 out of them. At the end of the 24 hours they are put in 

 water, where they remain until broken. When removed from 

 the water for the purpose of testing, break them at once ; if 

 this operation is delayed an hour or two the breaking strain 

 will be reduced. Such items as the temperature of the air, 



