OF MICROSCOPIC OBJECTS. 65 



sifting through coarse muslin, which will retain the Algse, 

 &c. The process of cleaning will vary according to circum- 

 stances. Some gatherings require to be boiled only a few 

 minutes in nitric acid; but the more general plan, where 

 they are mixed with organic or other foreign matter, is to 

 boil them in pure sulphuric acid until they cease to grow 

 darker in colour (usually from a half to one minute), and then 

 to add, drop by drop to avoid explosions, a cold saturated 

 solution of chlorate of potash until the colour is discharged, 

 or, in case the colour does not disappear, the quantity of 

 the solution used is at least equal to that of the acid. 

 This operation is best performed in a wide-mouthed ordinary 

 beaker glass,* a test-tube being too narrow. The mixture 

 whilst boiling should be poured into thirty times its bulk of 

 cold water, and the whole allowed to subside. The fluid 

 must then be carefully decanted and the vessel re-supplied 

 once or twice with pure water, so as to get rid of all the 

 acid. The gathering may then be transferred to a small 

 boiling-glass or test-tube, and the water being carefully 

 decanted boiled in the smallest available quantity of 

 nitric acid, and washed as before. This last process has 

 been found necessary from the frequent appearance of 

 minute crystals, which cannot otherwise be readily dis- 

 posed of without the loss of a considerable proportion of 

 diatoms. 



I may here mention that the washing-glasses used by 

 Mr. Rylands are stoppered conical bottles varying in 

 capacity from two ounces to one quart; the conical form 

 being employed to prevent the adherence of anything to the 

 side : they are stoppered, to render them available in the 

 shaking process about to be described. 



The gathering, freed from acid, is now put into two inches 

 depth of water, shaken vigorously for a minute or two, and 

 allowed to subside for half an hour, after which the turbid 



* These glasses are round, about six inches high, and usually contain 

 about eight ounces. They are rather wider at the bottom, tapering 

 gradually to the top, and may bo generally procured at the chemists, &c. 



