THE MADRAS HARBOUR. 



77 



crushers. On the platform it is mixed with the required 

 proportion of sand and cement, all carefully measured, and 

 these three ingredients are thrown together into one of a 

 number of pits in the platform ; at the bottom of each pit is 

 a door, and under the door a kind of cast-iron churn called a 

 mixer, into which the ingredients drop through the door. 

 Here a given quantity of water is added, the door of the 

 mixer closed, and the whole revolved a certain number of 

 times. The same engine as before works the mixers. The 

 mixer stops of its own accord when it has made the required 

 number of revolutions and with its door downwards. The 

 door is then opened, and the concrete, now completely mixed, 

 drops into a wooden box called a skip, of which two are 

 placed on a railway truck. The two skips being filled from 

 two adjacent mixers, the truck is run oif by three or four 

 coolies to the blockyard. Upon the platform of the block- 

 yard are placed strong wooden boxes with moveable sides, 

 the size of the blocks. A small hoisting crab upon a travel- 

 ling timber framing which spans the blockyard lifts the skip 

 from the truck and runs it over the wooden box, into which 

 its contents are capsized. There they are spread about and 

 trodden down, and a certain proportion of uncrushed lumps 

 of stone are added, so placed that each is completely sur- 

 rounded by concrete without touching either the sides of the 

 box or the neighbouring lump. These are simply to make 

 up the mass of the block with a material cheaper than the 

 true concrete. I should mention that the interior of the box 

 or mould is not quite unoccupied when the concrete is shot 

 into it. There are previously placed upon the floor within it 

 two small inverted wooden boxes, about ] 5 inches square and 

 12 inches high, and above these two vertical planks 9 inches 

 by three inches, the feet of which pass through the tops of 

 the boxes, and the tops stand above the top of the mould. 

 Bound these the concrete is rammed. These planks are 



