196 THE BOOK OF NATURE STUDY 



a balance, a beaker or two, a pestle made by sticking a small 

 rubber bung on the end of a glass rod, and two sieves, the first 

 of the finest woven brass wire, 100 meshes to the inch, and the 

 other made by cutting out a square from the bottom of a tin 

 box and replacing it by soldering on a piece of perforated zinc 

 with holes A- of an inch ( = i mm.) in diameter. 



Throw the soil on to this sieve, and when you have shaken as 

 much as possible of the fine earth through put the sieve under 

 the tap and let the water drip on its contents, which will be 

 the stones contained in the soil together with a good many 

 hard lumps of earth, especially with a clay soil. However, 

 these will break up in the water and after a little shaking under 

 the tap will wash away and leave behind the clean stones and 

 fine gravel more than i mm. in diameter, together with a 

 few fragments of roots and vegetation. The stones and gravel 

 should be dried and examined to see what they are made of, 

 whether they are water worn or angular, etc. ; we can also take 

 their weight and find what proportion they constitute of the 

 original soil, though the results will not mean very much when 

 the soil contains large stones. 



From the fine earth that passed the sieve, five grams are now 

 weighed out and put into a beaker on the side of which you have 

 made a mark three inches from the bottom. Add a little water to 

 the soil and churn it up into a smooth thin paste with the rubber 

 pestle, add more water until the beaker is full to the mark ; give a 

 good stir and let the contents settle for one minute exactly, then 

 pour the muddy water steadily and quickly into a jar without 

 disturbing the sediment collected at the bottom of the beaker. 

 Churn up again with the pestle, fill to the mark with water as 

 before, and again wait one minute before pouring off the turbid 

 top liquid. Repeat these operations until the top liquid becomes 

 clear during the minute's wait, because the only material now 

 left in the beaker is so coarse grained that it will fall to the bottom 

 in less than a minute. It will now be seen that by this process 

 the soil has been separated into clean sand that lies in the beaker 

 and finer clay like stuff which has been poured away in the turbid 

 top liquid. Keep a j ar full of this turbid water for a few days ; it will 

 settle down very slowly, but when it does clear pour off as much 



