i 
68 EDWARDS, ON CLEANING DIATOMACES. 
found to answer all the purposes of distilled, water, which is 
much more troublesome to procure, and then only by a 
tediously slow process. Every time it is washed, the water 
is allowed to stand on it for at least twenty-four hours. It is 
thus washed until the water takes up no more salts and runs 
off perfectly clear. The two or three last washings may be, 
with advantage, made with boiling water. 
After every washing, we must make sure that all the guano 
has settled, that none of the finer forms may be carried over 
with the water, when it is poured off, and lost. When the 
washing is complete the guano is intreduced into a capacious 
chemists’ beaker-glass, and there is poured on it sufficient 
chlorohydric acid to cover it to the depth of an imch and 
a half, when it is boiled for about an hour. It is then well 
washed with filtered water, and nitric acid made to replace 
the chlorohydric. The boiling of the nitric acid is now kept 
up until no more red fumes are given off, and the deposit is 
again well washed several times. ‘Thus far this process is the 
same as that recommended in the books, but the undissolved 
portion is not colourless; we have, therefore, to proceed with 
the following manipulations. 
- The deposit which now remains, after the boiling in acid, 
is well washed until the water comes off perfectly clear and 
almost free from acid; it is then covered to about the depth 
of an inch with sulphuric acid, and boiled until all the organic 
matter contained in it is charred, which is known by its 
turning black. Sometimes, however, the organic matter is 
in such small quantity that it hardly shows signs of colora- 
tion. When such is the case, it is always better to boil the 
acid for a short time before proceeding to the next step in the 
operation. The fumes given off in this and the next stage of 
the process are extremely unpleasant in odour and effects, so 
that care should be taken not to inhale any more of them 
than can possibly be helped, as they are apt to inflame the 
air-passages and cause severe sore throat. The best method 
is to conduct this portion of the process in the open air, or 
under a chimney haying a good draught. 
Whilst the sulphuric acid is undergoing ebullition, finely 
pulverized chlorate of potassa in very small quantities is 
added from time to time, always allowing the violent action 
resulting from the introduction of one portion to completely 
subside before another is introduced. During this portion 
of the process the hand should not be exposed to the vapours 
given off, as they will act on and ‘corrode the skin; the 
chlorate may be introduced by means of an ivory spatula—a 
metal one would be corroded. The heat is kept up all the 
