38 PREPARATION AND MOUNTING 



of the additional information thus acquired, but also because it 

 often happens that a specimen should be mounted in fluid (see 

 Chapter IV.) in the condition in which it is gathered, as well as 

 cleaned and mounted in balsam (Chapter III.) and dry. 



Where the gathering is taken from sand, the whole may be 

 shaken up in water as a preliminary operation, when much of the 

 sand will be separated by its own weight. The lime test, how- 

 ever, should be applied, viz. a small portion of hydrochloric 

 acid, and if there be effervescence it must be dissolved out by 

 this means. From Algae and other weeds diatoms may be de- 

 tached by agitating the whole together in a weak solution of 

 nitric acid about one of pure acid to twenty or thirty of water, 

 as it must be sufficiently weak to free the diatoms without des- 

 troying the matter to which they adhere. The diatoms may then 

 be separated by sifting through coarse muslin, which will retain 

 the Algse, &c. The process of cleaning will vary according to 

 circumstances. 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 disap- 

 pear, 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 mix- 

 ture while boiling should bo 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 gather- 

 ing 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 



* 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 be generally procured at the chemists, &c. 



