62 MOUNTING AND PREPARATION OP OBJECTS. 



the end of that time its liquid contents are trans- 

 ferred to another tumbler which we shall call number 

 2, number 1 being* filled and shaken or stirred with 

 a wooden rod, after standing five minutes its fluid 

 contents are transferred to a number 3, number 1 is 

 again filled and stirred, left to stand for five minutes, 

 at the end of which time the liquid in number 2 is 

 transferred to a number 4, and the contents of num- 

 ber 1 put in its place ; number 1 being again filled 

 and left standing five minutes, the contents of num- 

 ber 3, are transferred to a number 5 and the fluid of 

 number 1 put in its place; numbers 4 and 5 are 

 allowed to stand a quarter of an hour, the changes 

 being regulated in the other tumblers to suit this, by 

 adding 6 and 7 to them and so on till we manage to 

 collect 12 single tumblers, whose contents represent 

 washings lasting from 5 to 60 minutes respectively, 

 this process will take a long time as the washings 

 multiply indefinitely ; towards the end some of the 

 tumblers will be found to contain all the diatomacese 

 tolerably free from impurities. The labour is not so 

 great as might appear at first sight, for every tum- 

 bler that has undergone twelve washings is put 

 aside. 



Any flocculent matter remaining in the washed 

 deposits may be removed by pouring the water con- 

 taining the deposit gently upon an equal quantity of 

 glycerine in a test tube, so as to cause as little admix- 

 ture of the two liquids as possible. The diatoms on 

 account of their greater specific gravity sink to the 

 bottom, leaving the flocculent matter on top. 



