THE MECHANICAL ANALYSIS OF AKID SOILS 



37 



A slightly more effective disintegration of the soil aggregates is had by simple heating 

 with the dilute sodium carbonate solution. The soil tested above gave the results as 

 follows : — 



The above results were obtained by the use of the centrifugal machine. If the method 

 of sedimentation in beakers is employed, the boiling method offers the great disadvantage 

 that the number of decantations is very much increased. It is possible that while 

 the clay particles are disintegrated by the boiling, they gradually combine again to a 

 certain extent after the liquid cools. 



We have found that , by far the most effective agent in bringing about the 

 deflocculation of the clay is an ordinary camel-hair brush. It is employed as 

 follows : The weighed portion of soil is placed in a beaker (or enamelled iron cup) 

 and water cautiously added, sufficient to form a thick paste. The mixture is then 

 stirred with the brush. The clay is rapidly puddled and the mixture becomes so 

 tenacious that a further addition of water is required. Tliis is made very carefully, 

 a few drops at a time, and the puddling continued for from five to ten minutes. 



There appears to be no objection to carrying out the puddling in a beaker. One of 

 these, used for several successive operations, was found not to have lost even a milligramme. 



For arid soils, which contain considerable calcium carbonate (and, not infrequently, 

 calcium sulphate) it is essential that all water used should contain sodium carbonate 

 in about the proportion already indicated. 



The further treatment of the soil, after the above operation, depends upon the method 

 to be employed. If one of sedimentation, the mixture is made up to a height of say 

 ten centimetres and allowed to stand for a length of time depending upon the size of soil 

 particles which is taken as limiting the clay {vide infra). We have adopted what is 

 practically the 8-hour subsidence, which includes, in the clay division, particles up to about 

 0002 millimetre. After, usually, the third decantation, the residue, from which most of 

 the water should be removed on the water-bath, is again puddled for about a minute, 

 after which no further puddling is required, the residue being simply mixed with successive 

 portions of water (containing sodium carbonate) and allowed to stand for the specified time 

 until the liquid becomes practically clear at the end of that time. 



As already stated, the brush method of puddling has been found to be more effective 

 than any that we have tried. No matter what be the method of analysis adopted, its 

 use at one or more stages of the process is strongly recommended. Its eflSciency as 

 compared to that of the rubber pestle recommended by Hall and others is most striking. 

 Using the rubber pestle and employing the Hall method (of acid treatment followed by 

 ammonia) we have frequently had to decant as often as 20 to 30 times before the water 

 came away clear. The analysis carried out in this fashion may take more than a month 

 for its completion. By the aid of the brush and the use of sodium carbonate, the wiiole or 

 practically the whole of the clay may usually be removed in five decantations. 



Use of a 

 camel-hair 

 brush in 

 puddling the 

 clay 



Great 



acceleration of 

 analysis by 

 the brush 

 and sodium 

 carbonate 

 method 



