316 The Shrinkage of Soils 



almost in contact with the scale on the supporting frame. The reading 

 of each point against the scale was made by means of a telescope. It 

 was found that in this way the readings could be made to '01 cm. 

 The method followed in carrying out an experiment was to take readings 

 of the two points on the scale and of the weight of the block at half 

 hourly intervals until shrinkage had ceased, after which the block 

 was dried to constant weight in the hot air oven at 110° C.^ 



In preparing the blocks of soil for a series of readings, the fine 

 earth sample was employed, that is to say all particles having a diameter 

 larger than 1 millimetre were removed by sifting. The amount of 

 water requiring to be added to each sample under examination per 

 100 grms. of air-dry soil in order to produce maximum plasticity having 

 been previously determined, the calculated amount of water was added 

 in small quantities at a time, to a known weight of soil accompanied 

 by thorough kneachng, and the well-kneaded soil then moulded into a 

 brick of the proper size by means of a wooden mould. The mould 

 in question consisted of two wooden uprights fixed to a base afc the 

 required distance apart. In making a block the mould was hned with 

 thin paper, the mould then filled with soil, the well-kneaded soil being 

 pressed down tightly in the mould by means of a steel spatula ; when 

 sufficient soil had been transferred to the mould the paper fining was 

 removed carrying the block with it ; • the ends of the block were trimmed 

 by means of a sharp knife so as to reduce it to the proper length, the 

 block inserted in the cage, the end of the cage closed, the two glass 

 pointers inserted into the block, the cage placed in the support, the 

 cage and support suspended from the metal rod in the drying chamber, 

 and the series of observations commenced. 



The plan of drying the blocks in a wire cage was adopted on account 

 of difficulties experienced in the earlier stages of the work owing to 

 uneven evaporation from different sides of the blocks, resulting in a 

 tendency on the part of the blocks to buckle upwards, thus vitiating 

 the observations of the shrinkage. The endeavour was first made- to 

 circumvent the difficulty by allowing the blocks to dry on a suspended 

 wire gauze tray but this was not entirely satisfactory ; the plan finally 

 adopted of allowing the blocks to dry in a wire gauze cage was found 

 to give very satisfactory results. 



^ In the event of it not bcin^ possible to complete a series of readings in one day- 

 it was found that by removing the dish containing the sulphuric acid the readings could 

 be interrupted over night and resumed the next morning without seriously disturbing 

 their continuity. 



