38 



HEPOUT 01'' (JHEMlCAlj LAliOKATOKY 



The following exporiments were made in order to determine the rate at which the 

 clay is removed : — 



Clay, per cent, of total present 



Technique fur 

 using the 

 brush 



These results were compared with those of the method by boiling with dilute 

 sodium carbonate solution. It was found that when boiling was adopted, not only was 

 more than double the number of decantations required, but the sum total of the clay 

 removed was 51-5 per cent, as against 54 per cent, by the use of the brush. Examination 

 of the soil particles under the microscope shows the particles of sand and silt to be 

 quite clean when the brush is used, which is not the case with the method by boiling. 



As the camel-hair brush picks up and retains a considerable quantity of the soil, 

 care must be taken to remove this by agitation in successive portions of distilled water in a 

 small beaker, the whole of the separated sand being washed out of the beaker after each 

 washing. Usually four or five washings are sufficient. Tapping the bottom of the beaker 

 with the brush submerged in the water, has been found the most efficient method of 

 dislodging the sand. 



In order to avoid the frequent washing of the brush, which, while it need only be 

 employed twice in each determination, is nevertheless advantageously applied to bring the 

 clay into suspension after each decantation, it is best to use a separate brush for each soil 

 operated on, and to wash out only once at the end of the process. The brush is 

 conveniently kept in the small beaker in which the operation of washing is carried out 

 at the end. 



Any form of camel-hair brush may be applied to the above purpose. We have found 

 the flat form about half an inch broad, bound to a wooden handle by a strip of tin, to 

 be very convenient. Paraffin wax should be applied to the tin junction in order to fill the 

 interstices and prevent the entrance of soil. 



The round form of brush may also be used, a glass rod being inserted into the quill, 

 (which is cut rather short) and fastened by wrapping with thin copper wire. The junction 

 should be protected by wax as noted above. 



Cleaning of the brush after each puddling is more readily accomplished if the hairs be 

 cut moderately short. 



Where a great number of soils are to be operated upon, the labour of the preliminary 

 puddling may be avoided by substituting agitation with water and sodium carbonate in the 

 mechanical shaker, as described above. After the fourth decantation the residue (from 

 which some of the water should be removed on the water-bath) need be puddled by the aid 

 of the brush for about one minute onlv. The results obtained in this way have been, 



